Contact monitoring device

Abstract

This invention relates to a contact monitoring device (100) for monitoring the switching process of an electrical contact (101) having two contact states. The contact monitoring device (100) has an oscillator circuit (103) and a coupling element (105) having a signal input (107) and a signal output (109). The oscillator circuit (103) is connected upstream of the signal input (107) and applies an excitation signal to the coupling element (105). The coupling element (105) is designed to convert the excitation signal into a contact monitoring signal and apply it to the electrical contact (101). A first or second impedance value is applied to the oscillator circuit (103) through the electrical contact (101), depending on the contact state. The oscillator circuit (103) is designed to generate resonance at the first impedance value and output the type of excitation signal. Furthermore, the contact monitoring device (100) includes a detector (113) designed to detect the type of excitation signal in order to monitor the switching process of the electrical contact (101).

Description

TECHNICAL FIELD

[0001] The present application relates to a contact monitoring device for monitoring electrical contacts, in particular for monitoring the switching process of a switch contact, the functional state of an overcurrent protection and / or the functional state of an overvoltage protection. BACKGROUND

[0002] In electrical automation, switches can be used to switch actuators, wherein it can be necessary to detect whether the switch contacts of the switch are actually closed. This monitoring feedback can be implemented, for example, by means of additional auxiliary contacts. Alternatively, a forced contact guidance can be implemented to prevent incorrect switching of the switch, but this increases the production costs. For example, a faulty switch contact can have a defective, in particular welded, switching surface or a degraded semiconductor layer, so that it cannot be closed or opened against an applied contact signal or against a mechanical actuation.

[0003] The monitoring of switch contacts is particularly necessary for machine controls and device controls, wherein, for example, a switch relay is used, the switch contacts of which are frequently switched. Such contacts are subject to greater wear. The relay can be designed in such a way that the switch contacts can withstand, for example, several hundred thousand switching processes. Using a contact monitoring device, the contact state can be monitored and a message indicating the wear state can be issued as soon as the first signs of increased wear appear. An operator can then replace the contacts in the form of a relay, for example, at an early stage.

[0004] Such a contact monitoring device is known in principle. It usually works on the basis of an oscillating circuit, which is influenced by the switch contacts. In one switching state, the damping of the oscillating circuit is lower, while in the other switching state, the damping is higher. As a result, at least the oscillation amplitude changes, which can be measured, for example, by means of a voltage drop over a resistor.

[0005] DE 10 2018 114 425 A1 shows a specific example of such a contact monitoring device. Here, a contact monitoring device is described by way of example of a monitoring relay switch contact. An excitation signal is provided for the oscillating circuit by a signal generator via a transformer. However, the oscillating circuit can have temperature-dependent properties, which can cause problems in the reliability of the amplitude change measurement.

[0006] From JP 2012 211 855 A, a solution for a temperature-compensated oscillating circuit is known. Here, a FET transistor is used to set the resonance frequency of the oscillating circuit, the operating point of which is temperature-compensated by using a thermistor in a voltage divider for setting the operating point. The temperature-compensated oscillator is applied to a radar sensor of a vehicle. The FET transistor of the oscillator is also used as a frequency-determining element there, since the transistor capacitance together with the coil forms the oscillating circuit. When adjusting the operating point, the transistor capacitance changes, and the resonance frequency changes with it.

[0007] However, the known solutions for contact monitoring circuits have the disadvantage that they cannot reliably distinguish between correct functioning and faulty behavior of the contact, or that they require complex structures for this, and are therefore complex and expensive. In addition, existing contact monitoring devices have problems with temperature dependence. There is therefore a need for an improved contact monitoring device in which, in particular, the reliability of the contact monitoring is improved and only a small number of inexpensive components are required. This is recognized within the scope of the present application. SUMMARY

[0008] This object is solved by the features of independent claim 1. Advantageous embodiments are the subject of the dependent claims, the description and the drawings.

[0009] The present disclosure is based on the recognition that the above object can be solved by a contact monitoring device which is designed to generate a contact monitoring signal at an electrical contact by means of an oscillator circuit, and a coupling element and a damping element downstream of the oscillator circuit, in particular when the electrical contact is in a closed contact state. In one form, the oscillator circuit cannot oscillate in the case of an open contact state of the electrical contact, so that no contact monitoring signal is generated.

[0010] In another form, the oscillator circuit is also able to oscillate in the open contact state, but with a different resonant frequency. This can be achieved, for example, by switching in another capacitance in the oscillation loop at the time of contact switching, so that a different total capacitance comes into effect in the LC oscillation loop. If the contact is faulty, it no longer closes correctly and no longer resonates, or no longer resonates in another way, during the switching process. This is detected and displayed accordingly.

[0011] In a general embodiment, when the electrical contact is in a first contact state, a first damping element is active on the oscillator circuit, which leads to a first impedance curve in the oscillator circuit, and when the electrical contact is in a second contact state, the first damping element is deactivated and / or a second damping element is active on the oscillator circuit, which leads to a second impedance curve of the oscillator circuit, wherein the oscillator circuit is designed to generate a resonant oscillation when the electrical contact is in the first contact state and has the first impedance curve, and to output an excitation signal; and in the case of the electrical contact being in the second contact state and having the second impedance curve, to generate no resonant oscillation and to output no excitation signal, or to generate a different resonant oscillation and to output a different excitation signal; wherein a detector is designed to detect the excitation signal and the different excitation signal or the absence of an excitation signal, in order to monitor the electrical contact. The different resonant oscillation is generated when another frequency-determining element in the oscillator circuit is active as a result of a change in the contact state.

[0012] In an expanded embodiment, a device for thermally stabilizing the oscillator circuit is provided in the oscillator circuit. In this case, the oscillator circuit has an oscillation loop with a feedback branch and an amplifier, wherein the amplifier amplifies the signal fed back by the feedback branch.

[0013] The solution then provides that the amplifier has at least one transistor whose gain can be adjusted by its operating point, wherein the gain of the at least one transistor is stabilized using the device for thermal stabilization. This is done by changing the device for thermal stabilization when the temperature changes, which shifts the operating point of the transistor. Even if the temperature changes, this automatically keeps the gain of the transistor constant.

[0014] In a preferred variant, a thermistor, in particular an NTC or PTC resistor, as an element of a voltage divider, is used as the device for thermal stabilization. The NTC resistor corresponds to a negative temperature coefficient thermistor (Heiβleiter), the PTC resistor corresponds to a positive temperature coefficient thermistor (Kaltleiter). Alternatively, a semiconductor diode can also be used as a negative temperature coefficient thermistor, which is connected in the blocking direction. By changing the resistance of the thermistor, the operating point of the transistor is shifted, so that the gain factor remains stable.

[0015] In another embodiment, a temperature sensor is used as the device for thermal stabilization, the signal of which is analyzed by a microcontroller, which generates a corresponding correction signal, which sets the operating point of the at least one transistor for thermal stabilization.

[0016] Here, the microcontroller can generate a PWM signal, a correction signal in the form of a pulse width modulated signal, and an averaging device can be used, which outputs the average value of the PWM signal depending on the duty cycle. The operating point is set with the average correction signal.

[0017] In a cost-effective variant, the averaging device is formed in the form of a low-pass filter consisting of a resistor and a capacitor.

[0018] This form of thermal stabilization has the advantage that temperature compensation can be carried out very precisely. However, this solution is relatively expensive.

[0019] The contact monitoring signal can be, in particular, a high-frequency auxiliary energy, which is generated by the oscillator circuit and coupled into the load circuit with the electrical contacts by a coupling element. Impedance changes of the load circuit, in particular due to switching of the electrical contacts, are fed back to the oscillator circuit by the coupling element and generate a signal change between the oscillator circuit and the coupling element, which can be used to detect the switching of the electrical contacts.

[0020] According to a first aspect, the disclosure relates to a contact monitoring device for monitoring an electrical contact having a first contact state and a second contact state. The electrical contact can be, inter alia, a switching contact which is closed in the first contact state and open in the second contact state. For example, the electrical contact can have a low resistance in the first contact state and a high resistance in the second contact state.

[0021] The contact monitoring device comprises an oscillator circuit designed to generate an excitation signal, and a coupling element having a signal input and a signal output. The oscillator circuit is connected upstream of the signal input in order to apply the excitation signal to the coupling element, and the coupling element is designed to convert the excitation signal into a contact monitoring signal and output the contact monitoring signal at the signal output for application to the electrical contact.

[0022] A first impedance value is set on the oscillator circuit when the electrical contact is in the first contact state, and a second impedance value is set on the oscillator circuit when the electrical contact is in the second contact state. The oscillator circuit is designed to generate a resonant oscillation in the case of the electrical contact being in the first contact state and having the first impedance value, and to output a type of excitation signal, for example an excitation signal having a varying amplitude, in particular a damped excitation signal.

[0023] In one embodiment, the output of the excitation signal is suppressed with the electrical contact being in the second contact state and the second impedance value.

[0024] Furthermore, the contact monitoring device comprises a detector designed to detect the type of excitation signal and / or a change in the excitation signal in order to monitor the electrical contact.

[0025] The first impedance value can in particular be greater than the second impedance value. Furthermore, a damping element can be provided to set the first impedance value and / or the second impedance value at the signal input, in particular depending on the respective contact state of the electrical contact.

[0026] The electrical contact can be conductive in the first contact state and non-conductive in the second contact state. The contact monitoring device can in particular be designed to not apply the contact monitoring signal to the electrical contact permanently, in order to prevent a particularly high-frequency contact monitoring signal from being coupled via the electrical contact into a load circuit which in particular guides low-frequency signals for a long time. An advantage of an improved EMC behavior of the contact monitoring device can accordingly be achieved.

[0027] The electrical contact can be a power switching contact of an electromechanical relay, a semiconductor relay, a contactor, a reed contact or a mechanical switch. The electrical contact can in particular be designed to have a first ohmic resistance in the first, in particular closed, contact state and a second ohmic resistance in the second, in particular open, contact state, wherein the first ohmic resistance is smaller than the second ohmic resistance. In particular, the electrical contact has a low resistance in the closed contact state and a high resistance in the open contact state.

[0028] The electrical contact can be a fuse, in particular a fuse link, which is conductive or has a low resistance in the first contact state and is non-conductive or has a high resistance in the second contact state in which the fuse has triggered.

[0029] Furthermore, the first contact state can be a first switching state of the electrical contact, in particular of the electrical switching element, and the second contact state can be a second switching state of the electrical contact, in particular of the electrical switching element.

[0030] In one embodiment, the contact monitoring device is designed to apply the contact monitoring signal to the electrical contact as a differential signal, which is a current signal that causes a small voltage drop over the small contact resistance, in particular in the electrical contact in the first contact state. Thereby, it is achieved, inter alia, that the contact monitoring signal in the electrical contact has a low amplitude and, accordingly, only a small high-frequency signal component is superimposed on the useful signal flowing through the electrical contact. As a result, the EMC properties of the contact monitoring device can be improved.

[0031] In one embodiment, the oscillator circuit is designed to generate the excitation signal in the high-frequency range, preferably with a frequency in the range from 1 MHz to 100 MHz, more preferably with a frequency of 50 MHz. Thereby, it is achieved, inter alia, that the frequency separation of the contact monitoring signal and the useful signal by means of cost-effective frequency filter elements is possible. The oscillator circuit can be a high-frequency generator, which is connected to the electrical contact, in particular in parallel, by means of a coupling element and a damping element.

[0032] In one embodiment, the oscillator circuit comprises a self-oscillating oscillator, which has, in particular, a variable resonance frequency and is designed to generate an electromagnetic oscillation when the electrical contact is in the first contact state, in particular in the low-resistance closed contact state.

[0033] In one embodiment, the damping element is designed to set a first impedance value at the signal input when the electrical contact has the second contact state. Accordingly, the oscillator circuit can be designed to generate the excitation signal when the electrical contact is open or not to generate the excitation signal when the electrical contact is closed.

[0034] By monitoring the electrical contact of the relay by means of the contact monitoring device, it is possible to generate switching information about the transition of the electrical contact between the first contact state in which the electrical contact is non-conductive and the second contact state in which the electrical contact is conductive when the contact signal is applied to the electrical contact. Thereby, it can be ensured that the relay switches with the contact signal and, accordingly, there is no fault in the electrical contact and / or the magnet system of the relay. Accordingly, if the contact signal is present on the relay and the electrical contact does not switch, a functional fault of the relay can be determined. Furthermore, it is also possible to monitor the opening of the relay when the contact signal disappears.

[0035] The contact monitoring device has the advantage that, from the point of view of functional reliability, in particular in accordance with the IEC 61508 standard, the contact state of the relay switch contact can be clearly detected. As a result, a higher degree of diagnostic coverage can be achieved.

[0036] The detector can in particular be designed to convert the change in the excitation signal or the change in the contact monitoring signal into an output signal, which can be a time-discrete and / or amplitude-discrete signal, in particular a binary signal and / or a digital signal. A first output signal amplitude can correspond to a first contact state or a closed electrical contact, and a second output signal amplitude can correspond to a second contact state or an open electrical contact. The detector can be designed such that the output signal or its type matches the change in the excitation signal and / or the contact monitoring signal instantaneously or with as little time delay as possible. The change in the excitation signal can in particular be based on a changeover between generating the excitation signal on the basis of the resonance condition of the oscillator circuit being met and not generating the excitation signal on the basis of the resonance condition of the oscillator circuit not being met.

[0037] In one embodiment, the formation of the resonant oscillation is suppressed in the second contact state, thereby preventing the output of the excitation signal.

[0038] In one embodiment, the oscillator circuit is designed to generate the excitation signal with an excitation frequency corresponding to a resonance frequency of the oscillator circuit using a first impedance value, wherein the oscillator circuit is further designed to change the signal amplitude of the excitation signal on the basis of the impedance value at the signal input. The oscillator circuit can be designed to switch from an inoscillatable state to an oscillatable state with a change in the impedance value at the signal input, wherein the signal amplitude of the excitation signal can also change continuously with a continuous change in the impedance value. The oscillator circuit is further designed to transition from the inoscillatable state to the oscillatable state when an impedance limit value is exceeded at the signal input.

[0039] In one embodiment, the contact monitoring device comprises a damping element, which is connected downstream of the signal output and coupled to the electrical contact, for example upstream or downstream, wherein the damping element is designed to provide an impedance when the electrical contact is in the second contact state, thereby preventing the effect of the impedance of the electrical contact in the second contact state, wherein by the action of the damping element, the signal input of the coupling element is damped, the oscillator circuit cannot oscillate and the output of the excitation signal is prevented.

[0040] In one embodiment, the coupling element and the oscillator circuit are designed to form an oscillation loop, wherein the damping element is designed to dampen the oscillation loop in the second contact state to reduce the signal amplitude of the excitation signal.

[0041] In one embodiment, the damping element is coupled to the electrical contact, for example in parallel electrical connection, wherein the damping element is bridged with low resistance and the damping of the damping element coupled to the signal input by means of the coupling element is reduced when the electrical contact is in the first contact state. The oscillator circuit is designed to generate the excitation signal with increased signal amplitude with reduced damping.

[0042] In one embodiment, the oscillator circuit has a detector output and is designed to provide the excitation signal or a type of the excitation signal to the detector via the detector output.

[0043] In one embodiment, the detector is designed to convert the excitation signal into an output signal and to output the output signal in at least two different signal states, wherein a first signal state of the at least two signal states indicates a closed electrical contact and a second signal state of the at least two signal states indicates an open electrical contact.

[0044] In one embodiment, the detector is designed to output the output signal in a first signal state when an oscillating excitation signal is present at the detector output and to output the output signal in a second signal state when a non-oscillating excitation signal, a signal amplitude of the excitation signal is below an amplitude limit value and / or the excitation signal is not present at the detector output.

[0045] In one embodiment, the coupling element is designed to electrically isolate the oscillator circuit and / or the detector from the electrical contact current.

[0046] In one embodiment, the coupling element is designed as a direct electrical connection, for example a cable connection, to the contact of the oscillator circuit, so that a change in the electrical contact can have a direct effect on the impedance of the oscillator circuit.

[0047] In one embodiment, the detector is designed to detect a change in the actuation signal and the excitation signal for switching the electrical contact and to output a binary fault signal, which indicates whether the electrical contact is switched in accordance with the actuation signal. Thereby, the advantage can be achieved that the detector can detect whether the actuation signal and the excitation signal carry the same logical information about the contact state of the electrical contact. The actuation signal can in particular be provided to the detector via a switch control terminal.

[0048] The detector can also be designed to detect a first logical information when an excitation signal or a resonant oscillation is present at the detector input and to detect a second logical information when an actuation signal is present at the switch control terminal. Furthermore, the detector can be designed to compare the first logical information with the second logical information.

[0049] The detector can be designed to generate an output signal based on a comparison of the first logical information and the second logical information, wherein the output signal indicates a conformity or a deviation of the first logical information with respect to the second logical information. The first logical information can be binary switch information about the electrical contact, which is intended to trigger a switching of the electrical contact, in particular, and the second logical information can be binary test information describing a contact state of the electrical contact, in particular. The binary test information can provide information about an electrical conductivity of the electrical contact, in particular.

[0050] Using the binary switch information and the binary test information, four different signal combinations can be realized (see Table 1).

[0051]

[0052] Table 1: Possible combinations of switch information and test information

[0053] Depending on the signal combination, the detector can be designed to generate an output signal with a signal level representing a logical 0 in cases 1 and 4 and to generate an output signal with a signal level representing a logical 1 in cases 2 and 3. Alternatively, different signal combinations can correspond to respective amplitude values of the output signal or to output signal patterns. The output signal pattern can be realized, for example, by explicit sequences of signal pulses, in particular with different pulse lengths.

[0054] In one implementation form, the detector is designed to detect the excitation signal within a predetermined time interval after receiving the contact signal in order to determine whether the electrical contact is switched in accordance with the contact signal within the predetermined time interval.

[0055] In one implementation form, the contact monitoring device comprises an optical display element designed to display the detection of the contact signal and the respective detected switching of the electrical contact or a deviation from the expected contact signal.

[0056] In one implementation form, the coupling element comprises a transformer having a first inductance and a second inductance, wherein the first inductance is inductively coupled to the second inductance in order to convert the excitation signal into the contact monitoring signal.

[0057] In one implementation form, the coupling element comprises a transformer comprising a first air coil and a second air coil which are inductively coupled to each other. The first air coil and the second air coil can be cylindrical coils or toroidal coils. Furthermore, a coil core, in particular a ferrite core or a magnetic core, can be arranged inside the first air coil and / or inside the second air coil, respectively. In one implementation form, the magnetic core can be arranged partially in the first air coil and / or in the second air coil. The coil core can be formed by a ferrite plate or a ferrite foil which guides the magnetic flux.

[0058] A transformer having a first inductance and a second inductance, which are formed as air coils, for example, achieves the advantage that the coils can be produced using printed circuit board technology and that the number of discrete electronic components can be reduced accordingly when producing the contact monitoring device. Furthermore, the capacitive elements of the contact monitoring device can also be designed as printed circuit board capacitors in order to further reduce the number of discrete electronic components.

[0059] By implementing the inductances of the transformer as planar coils, the advantage of cost-effective production of the contact monitoring device can be achieved, in particular, since the inductances are not implemented as ferrite plates, for example. The transformer can be designed, in particular, such that a coupling factor of more than 20% is achieved for coupling the excitation signal from the first inductance to the second inductance in order to effectively convert the excitation signal into the contact monitoring signal.

[0060] In one embodiment, the contact monitoring device comprises an impedance circuit which is connected downstream of the signal output and coupled to the damping element, for example, upstream, wherein the impedance circuit is designed to compensate for the leakage inductance and / or the stray capacitance of the coupling element in the case of the contact monitoring signal having a predetermined frequency.

[0061] In one embodiment, the impedance circuit is designed for minimizing the total capacitance and / or the total inductance on the galvanic isolation of the coupling element.

[0062] In one embodiment, the contact monitoring device comprises a first filter element and a second filter element, wherein the electrical contact has a first output connection to which the first filter element is connected downstream and a second output connection to which the second filter element is connected downstream in order to damp high-frequency signals applied to the electrical contact and / or to an electrical load and / or to a voltage source coupled to the electrical contact by the coupling element.

[0063] The filter elements achieve the advantage, in particular, of separating the contact monitoring device from the external wiring function of the electrical contact, which is connected to the first output connection and to the second output connection, for example. The first filter element and / or the second filter element can comprise an inductance or a ferrite, respectively, which is designed to have a low resistance for low-frequency alternating signals and a high resistance for high-frequency alternating signals. In this way, the advantage can be achieved, in particular, that the filter elements can conduct low-frequency signals having a high current strength effectively.

[0064] The contact monitoring signal can preferably have a frequency of 100 kHz to 100 MHz. The filter elements have a high resistance for the contact monitoring signal in this frequency range, so that the contact monitoring signal is not present at the output connections or only with a reduced signal amplitude.

[0065] The filter elements furthermore achieve the advantage that a low-resistance bridging of the electrical contacts cannot be misinterpreted by the contact monitoring device as an electrical contact in the first contact state. In particular in the case of a contact monitoring signal having a predetermined frequency, the real part of the impedance value of the respective filter element can reach the order of magnitude of the ohmic resistance of the damping element. In this way, the specific advantage can be achieved that in the case of an electrical contact in the second contact state and an external low-resistance bridging of the electrical contacts, a damping value corresponding to the damping value set by the damping element can be achieved and oscillations of the oscillator circuit can be suppressed.

[0066] In one embodiment, the first filter element and / or the second filter element has an ohmic impedance component at the oscillator frequency which is designed to prevent an external short circuit of the first output connection to the second output connection from being detected as a closed electrical contact.

[0067] In one embodiment, the damping element comprises a capacitance formed by a printed circuit board capacitor.

[0068] In one embodiment, the contact monitoring device comprises a supply voltage connection to which a supply voltage can be applied, wherein the oscillator circuit and / or the detector can be supplied with electrical energy via the supply voltage connection. Furthermore, the contact monitoring device can have a switch control connection to which a switching signal can be applied in order to trigger the electrical contacts.

[0069] In one embodiment, a switching signal can be applied to the detector and / or the oscillator circuit via the switch control connection, wherein the detector and / or the oscillator circuit are designed to be supplied with electrical energy by means of the switching signal. The switching signal can in particular be a direct voltage signal which is suitable for providing electrical energy for the detector and / or the oscillator circuit. In one embodiment, the switching signal can be used to charge a buffer capacitor which is designed to provide a constant voltage and / or a constant current strength for the detector and / or the oscillator circuit at least for a predetermined time interval.

[0070] In one embodiment, a rectifier can be connected between the switch control connection and the buffer capacitor, the rectifier being designed to convert an alternating switching signal into a supply voltage for the detector and / or the oscillator circuit.

[0071] In one embodiment, the buffer capacitor is designed to continue to supply electrical energy to the detector and / or the oscillator circuit for a predetermined time interval when the switching signal is missing, in order to detect the opening of the electrical contacts corresponding to the disappearance of the switching signal and to generate a corresponding output signal. The detector can in particular be designed to output state information about a contact fault or state information about a correct switching of the electrical contacts on the basis of the switching signal using the output signal before the energy supply to the detector is interrupted. BRIEF DESCRIPTION OF DRAWINGS

[0072] Further embodiments are explained with reference to the accompanying drawings. In the drawings:

[0073] Figure 1 An embodiment of a contact monitoring device is shown;

[0074] Figure 2 An embodiment of a contact monitoring device is shown;

[0075] Figure 3 An embodiment of an impedance at a signal input is shown;

[0076] Figure 4 An embodiment of a contact monitoring device is shown;

[0077] Figure 5 An embodiment of a contact monitoring device is shown;

[0078] Figure 6 An embodiment of a contact monitoring device is shown;

[0079] Figure 7 A basic form of a temperature-compensated contact monitoring device is shown;

[0080] Figure 8 A basic form of a frequency-determining network of a contact monitoring device is shown;

[0081] Figure 9 Two impedance graphs of a frequency-determining network of a contact monitoring device are shown;

[0082] Figure 10 A first embodiment of a temperature-compensated contact monitoring device is shown;

[0083] Figure 11 A second embodiment of a temperature-compensated contact monitoring device is shown; and

[0084] Figure 12 A third embodiment of a temperature-compensated contact monitoring device is shown. DETAILED DESCRIPTION

[0085] Figure 1 A schematic diagram of a contact monitoring device 100 for monitoring an electrical contact 101 having at least two contact states according to an embodiment is shown. The contact monitoring device 100 has an oscillator circuit 103 for generating an excitation signal and a coupling element 105 having a signal input 107 and a signal output 109.

[0086] An oscillator circuit 103 is connected upstream of the signal input 107 in order to apply an excitation signal to the coupling element 105, which is designed to convert the excitation signal into a contact monitoring signal and to output the contact monitoring signal at the signal output 109 for application to the electrical contact 101. Furthermore, the contact monitoring device 100 comprises a damping element 111, which is connected downstream of the signal output 109 and upstream of the electrical contact 101.

[0087] A first impedance value is set at the oscillator circuit 103 when the electrical contact 101 is in the first contact state and a second impedance value is set at the oscillator circuit 103 when the electrical contact 101 is in the second contact state.

[0088] The contact monitoring device comprises a damping element 111, which is connected downstream of the signal output 109 and upstream of the electrical contact 101, wherein the damping element 111 is designed to provide an impedance when the electrical contact 101 is in the second contact state in order to dampen the impedance effect of the electrical contact 101 in the second contact state, wherein with the effect of the damping element 111 the signal input 107 of the coupling element 105 is damped, the oscillator circuit 103 cannot oscillate and the output of the excitation signal is prevented.

[0089] The first impedance value is greater than the second impedance value.

[0090] The oscillator circuit 103 is designed to generate a resonant oscillation and to output the excitation signal when the electrical contact 101 is in the first contact state and has the first impedance value and to suppress the output of the excitation signal when the electrical contact 101 is in the second contact state and has the second impedance value. Furthermore, the contact monitoring device 100 comprises a detector 113, which is designed to detect the excitation signal in order to monitor a change in the contact state of the electrical contact 101.

[0091] The damping element 111 comprises a resistor 129, which is designed to change or load the impedance value at the signal input 107 in such a way that the oscillation loop formed by the preferred inductive imaginary part of the coupling element 105 and the preferred capacitive imaginary part of the oscillator circuit 103 experiences a high damping with which the oscillator circuit 103 cannot oscillate and thus there is no contact monitoring signal at the electrical contact 101.

[0092] Furthermore, the damping element 111 comprises a capacitor 131, which is designed to produce a high first impedance for a useful signal, in particular of low frequency, applied at the electrical contact 101 via the output connection 125-1, 125-2, in order to minimize or prevent a leakage current generated by the damping element 111. Furthermore, the capacitor 131 is designed to produce a low second impedance for the contact monitoring signal in order to achieve a spectral separation of the contact monitoring signal and the useful signal.

[0093] The capacitor 131 has, in particular, a high electrical strength, for example greater than or equal to 30 kV / mm, wherein the capacitor 131 is preferably embodied as a printed circuit board capacitor. Thereby, in particular, the advantage of a reduced number of required discrete components can be achieved, so that a more cost-effective production can be carried out. Furthermore, thereby, the advantage of a reduced installation space of the contact monitoring device 100 can be achieved.

[0094] In one embodiment, the printed circuit board capacitor 131 comprises conductor surfaces arranged on different layers of the at least two-layer printed circuit board. Thereby, for example, the advantage can be achieved that, when the contact monitoring device 100 is used in a safety-relevant area, a functional failure of the contact monitoring device 100 based on a short circuit between the different layers of the printed circuit board can be reduced or excluded. In particular, a functional failure based on a short circuit between the different layers of the printed circuit board can be excluded in the error analysis, so that also the advantage can be achieved that the contact monitoring device 100 can be produced at reduced production costs.

[0095] When the electrical contact 101 is closed, i.e. the electrical contact 101 changes from the second contact state to the first contact state, the damping element 111 bridges with low resistance due to the parallel connection of the damping element 111 to the electrical contact 101 and thus has no influence on the useful signal and the contact monitoring signal applied on the electrical contact 101 accordingly. By the bridging of the damping element 111, the transformation damping produced by the resistor 129 of the damping element 111 is reduced at the signal input 107, so that the oscillation loop only has low ohmic losses. Furthermore, the oscillation loop is designed to produce a resonant oscillation with reduced damping.

[0096] The oscillator circuit 103 can be configured as a Colpitts oscillator comprising the capacitors 139-1, 139-2 and the transistor 141. The transistor 141 is designed for amplifying the excitation signal. Furthermore, the oscillator circuit 103 comprises the resistor 143 via which the excitation signal can be guided to the detector 113. The inductance 119-1, which can be formed as a coil, can form an element of the oscillator circuit 103.

[0097] The detector 113 can comprise a capacitor 145 which is designed for separating a direct current component of the excitation signal. Furthermore, the detector 113 comprises at least two diodes 147-1, 147-2 and a further capacitor 153, wherein the diodes 147-1, 147-2 and the capacitor 145 are designed for converting the excitation signal into a rectified output signal. Furthermore, the detector 113 has a resistor 149 and a transistor 151, wherein the transistor 151 is switched on by the resistor 149 when the oscillation generated by the oscillator circuit 103 is applied as excitation signal at the detector output 115. Furthermore, the detector 113 comprises a pull-up resistor 155, wherein the detector 113 is designed for providing an output signal, in particular an inverted signal, which outputs a logic 0 when the electrical contact 101 is closed or in the first contact state and a logic 1 when the electrical contact 101 is open or in the second contact state.

[0098] In one embodiment, the detector 113 comprises an output signal connection 161 and is designed for inverting the output signal so that a logic 1 is output at the output signal connection 161 when the electrical contact 101 is in the first contact state and a logic 0 is output at the output signal connection 161 when the electrical contact 101 is in the second contact state.

[0099] Furthermore, the contact monitoring device 100 comprises a supply voltage connection 157 to which a supply voltage can be applied, wherein the oscillator circuit 103 and / or the detector 113 can be supplied with electrical energy via the supply voltage connection 157. The supply voltage connection 157 can comprise a smoothing capacitor 159 which forms a smoothing capacitor for smoothing the supply voltage. Furthermore, the smoothing capacitor 159 can be embodied as a buffer capacitor which forms a provision for providing electrical energy to the oscillator circuit 103 and / or the detector 113 for a predetermined time interval, in particular also when an external energy supply via the supply voltage connection 157 is interrupted.

[0100] The coupling element 105 comprises a transformer 117 which forms an inductive coupling of the oscillator circuit 103 to the impedance circuit 121 and the damping element 111.

[0101] The impedance circuit 121 comprises capacitors 135-1, 135-2 which form a provision for compensating for a leakage inductance, in particular of the transformer 117 at a predetermined frequency of the excitation signal generated by the oscillator circuit 103. The capacitors 135-1, 135-2 realize, in particular, the advantages of a total capacitance minimization and / or the advantages of a symmetrical structure of the galvanic isolation by the coupling element 105. The capacitors 135-1, 135-2 can be formed, in particular, by capacitors having the same capacitance value.

[0102] Furthermore, the impedance circuit 121 comprises a capacitance 137-1, 137-2 and an inductance 133. In one embodiment, only one of the capacitances 137-1, 137-2 and / or only one of the capacitances 135-1, 135-2 can be provided.

[0103] The inductance 133 and the capacitances 137-1, 137-2 form an LC component which is designed to react to an electrical signal corresponding to an electrical line having a reversible impedance. The inductance value of the inductance 133 and the capacitance value of the capacitances 137-1, 137-2 can be selected such that the LC component has a high impedance value when the electrical contact 101 is in the first contact state, in order to switch the signal output 109 of the coupling element 105 to high ohmic and accordingly to be unloaded. Thereby, the impedance value at the signal input 107 can have a high real part with which the generation of an excitation signal by the oscillator circuit 103 can be suppressed.

[0104] Figure 2 A schematic diagram of a contact monitoring device 100 for monitoring an electrical contact 101 having at least two contact states is shown according to one embodiment. The contact monitoring device 100 is integrated into a module base 203, wherein the electrical contact 101 is part of a switching module 201. The module base 203 comprises three switching contact terminals 205-1, 205-2, 205-3, which are embodied in particular as a socket connector. Furthermore, the switching module 201 comprises corresponding plug-in contacts 207-1, 207-2, 207-3, which can be inserted into and electrically connected with the switching contact terminals 205-1, 205-2, 205-3, in order to connect the electrical contact 101 with the damping element 111, in particular in parallel therewith.

[0105] The electrical contact 101 can be in particular a three-pole switch which is designed to electrically connect the plug-in contact 207-3 and 207-2 in the first contact state and to electrically connect the plug-in contact 207-1 and 207-2 in the second contact state. The contact monitoring device 100 is designed to detect the opening and closing of the electrical connection between the plug-in contact 207-3 and the plug-in contact 207-2. The plug-in contact 207-1 can be guided to another contact monitoring device 100 via a feedthrough terminal 209 in order to also monitor the electrical connection between the plug-in contacts 207-1 and 207-2. Furthermore, the contact monitoring device 100 can be designed to apply a further contact monitoring signal to the plug-in contacts 207-1 and 207-2 via the sockets 205-1 and 205-2 in order to monitor the electrical connection between the plug-in contacts 207-1 and 207-2.

[0106] The contact monitoring device 100 has a filter module 211 which comprises a filter element 123-2. The filter element 123-2 can be formed by a single inductance, which is designed as an HF ferrite, in particular. By not using a further filter element, the advantage of reduced production costs can be achieved while the contact monitoring device 100 is reliably functioning.

[0107] The capacitance 131 of the damping element 111 can be formed as a printed circuit board capacitor to have an increased electrical strength. Furthermore, at least one of the capacitances 137-1, 137-2, for example the capacitance 137-1, is formed as a printed circuit board capacitor which is resistant to high voltages. The capacitances 137-1, 131 can preferably have a capacitance value in the range of pF, respectively. More preferably, the capacitances 137-1, 137-2 have a capacitance value of less than 100 pF, respectively. Furthermore, the other capacitances 135-1, 135-2 can also have a capacitance value in the range of pF or a capacitance value of less than 100 pF, respectively. By the low capacitance values, the following advantages can be achieved, in particular, for example in an AC application, a small, in particular negligible, leakage current flows through the impedance circuit 121 and / or the damping element 111.

[0108] The inductance 133 can be designed as a planar coil in the form of a spiral conductor track.

[0109] In one embodiment, the detector 113 can be designed to provide an output signal at the output signal connection 161 only when a switching error of the electrical contact 101 is present. The detector 113 can be designed to detect a switching error of the electrical contact 101 based on a logical deviation between the excitation signal and the contact signal for triggering the electrical contact 101.

[0110] The switching module base 203 can also have a first switching control connection 215-1 and / or a second switching control connection 215-2, to which a contact signal can be applied in order to trigger the electrical contact 101 in the switching module 201. The rectifier 213 is connected upstream of the first switching control connection 215-1 and / or the second switching control connection 215-2 and is designed to convert the contact signal into a rectified contact signal. Furthermore, the switching module base 203 comprises a first switching signal output 217-1 and / or a second switching signal output 217-2, wherein the rectifier 213 is designed to provide the rectified contact signal at the first switching signal output 217-1 and / or at the second switching signal output 217-2.

[0111] The switch module 201 comprises a first switch connection plug 219-1 and / or a second switch connection plug 219-2. The first switch connection plug 219-1 can be electrically connected to the first switch signal output 217-1 when the switch module 201 is plugged into the switch module base 203 and / or the second switch connection plug 219-2 can be electrically connected to the second switch signal output 217-2 when the switch module 201 is plugged into the switch module base 203 in order to apply a contact signal to the switch element.

[0112] In one embodiment, the contact signal can be fed to the detector 113, wherein the detector 113 is designed to analyze the contact signal with respect to the excitation signal in order to detect a switching and / or contact state of the electrical contact 101 from the contact signal and to provide a corresponding output signal at the output signal connection 161.

[0113] The capacitances 135-1, 135-2, 137-1, 137-2, 131, 139-1, 139-2, in particular coupling capacitors, can be formed by conductor surfaces arranged on different layers of the printed circuit board, respectively or as a subset. A plastic material of the printed circuit board can be arranged between the metallic conductor surfaces, thereby forming the capacitances as printed circuit board capacitors.

[0114] Furthermore, the contact monitoring device 100 comprises a supply voltage connection 157 to which a supply voltage can be applied, wherein the oscillator circuit 103 and / or the detector 113 can be supplied with electrical energy via the supply voltage connection 157. The supply voltage connection 157 can be formed by a supply terminal, in particular.

[0115] The contact monitoring device 100 further comprises a first load connection 221-1 and a second load connection 221-2, each connected downstream of the filter module 211. The first load connection 221-1 is electrically connected to the third switch contact connection 205-3 and the second load connection 221-2 is electrically connected to the second switch contact connection 205-2. In particular, the first load connection 221-1 can be connected to a load voltage source 223 and designed to apply a load voltage signal to the electrical contact 101 via the third switch contact connection 205-3 and the third plug contact 207-3.

[0116] The second load connection 221-2 can be electrically connected to an electrical load 225, wherein the load voltage signal is applied at the electrical load 225 when the electrical contact 101 is in the first contact state. Furthermore, the load connections 221-1, 221-2 can be short-circuited with a wire bridge 227. Thereby, for example, a test case for the contact monitoring device 100 can be generated in order to check a reliable identification of the contact state of the electrical contact 101 even in case of a low-ohmic bridging of the electrical contact 101, in particular in case of an external short circuit.

[0117] The coupling element 105 comprises a transformer 117 which is designed to inductively couple the oscillator circuit 103 to the impedance circuit 121 and the damping element 111. The transformer 117 has a first inductance 119-1, in particular a first planar coil, and a second inductance 119-2, in particular a second planar coil, wherein the first inductance 119-1 is inductively coupled with the second inductance 119-2 in order to convert the excitation signal into the contact monitoring signal. The transformer 117 is designed to galvanically isolate the oscillator circuit 103 from the impedance circuit 121, the damping element 111 and / or the electrical contact 101. The galvanic isolation is indicated by a separation line 229.

[0118] Figure 3 A frequency-dependent impedance at the signal input is shown in one embodiment. An inductance, in particular formed by the primary inductance of the transformer of the coupling element, acts on the signal input. For example, the inductance can have an inductance value of 200 nH. Furthermore, a capacitance, in particular formed by the capacitance of the oscillator circuit, also acts on the signal input. For example, the capacitance can have a capacitance value of 50 pF. Furthermore, an ohmic resistance acts on the signal input, in particular formed by the signal output side impedance transformed by means of the transformer. For the electrical contact in the first contact state, i.e. in the case of a closed, electrically conductive electrical contact, a first resistance with a resistance value of, for example, 4 kΩ can act on the signal input. When the electrical contact is in the second contact state, i.e. in the case of an open, electrically insulating electrical contact, a second resistance with a resistance value of, for example, 1 kΩ can act on the signal input.

[0119] The resistance acting on the signal input can change depending on the contact state in such a way that, in the case of the first resistance, the oscillator circuit is able to oscillate and can generate an excitation signal with a resonance signal amplitude, while, in the case of the second resistance, the oscillator circuit is not able to oscillate and cannot generate an excitation signal.

[0120] The oscillator circuit can be designed to change from the non-oscillatable state to the oscillatable state at a resistance limit value 301 of greater than 2.5 kΩ. The contact monitoring device 111 is formed by the respective dimensions of the electrical components, so that the first impedance curve 303 and the second impedance curve 305 are separated by a maximum possible amplitude difference. In this case, the amplitude difference can be proportional to the impedance difference at the signal input based on the first contact state and the second contact state. Under the first impedance curve 303, the oscillator circuit is in the non-oscillatable state and cannot generate an excitation signal. Under the second impedance curve 305, the oscillator circuit is in the oscillatable state and can generate an excitation signal.

[0121] Figure 4A schematic diagram of one embodiment of the contact monitoring device 100 is shown. The expected impedance in ohms of the expected oscillator frequency is given between the individual elements. The impedance of the electrical contact 101 in the first contact state or the closed electrical contact 101 is given above the schematic diagram of the contact monitoring device 100.

[0122] Furthermore, the impedance of the electrical contact 101 in the second contact state or the open electrical contact 101 is given below the schematic diagram of the contact monitoring device 100. The load 225 can have an impedance in the range from mΩ to ∞Ω.

[0123] A ferrite connection with an ohmic impedance component in the Ω range is connected downstream of the contact 101.

[0124] The damping element 111 and / or the filter element are designed to already provide the impedance in a defined manner between the damping element 111 and the impedance circuit 121 independently of the external circuit of the contact monitoring device 100, in particular independently of the external load 225. Thereby, the advantage can be achieved that the impedance value or impedance range is predetermined at this location when the electrical contact is opened.

[0125] In particular, an external or load-side short circuit can be prevented from causing an impedance on the oscillator circuit 103 even when the electrical contact 101 is opened, which allows the generation of an oscillation and thereby the generation of the excitation signal. Thus, an external short circuit can be prevented from being misinterpreted as a closed electrical contact 101.

[0126] The impedance circuit 121 can be designed to convert a small impedance on the switch contact side into a large impedance on the coupling element side when the electrical contact is closed. Furthermore, the impedance circuit 121 can be designed to convert a large impedance on the switch contact side into a small impedance on the coupling element side when the electrical contact is opened. The given impedance ranges correspond to the values of the impedance at the respective corresponding locations in the circuit based on the high-frequency range.

[0127] Figure 5 A schematic diagram of one embodiment of the contact monitoring device 100 is shown. The electrical contact 101 is an overcurrent and / or overvoltage protection device, in particular a fuse. The expected impedance in ohms is given between the individual elements. The impedance of the electrical contact 101 in the first contact state or the non-triggered fuse is given above the schematic diagram of the contact monitoring device 100.

[0128] Furthermore, the impedance of the electrical contact 101 in the second contact state or the triggered fuse is given below the schematic diagram of the contact monitoring device 100. The load 225 can have an impedance in the range from mΩ to ∞Ω.

[0129] If the electrical contact 101 is closed or conducting, the oscillator circuit 103 cannot oscillate. If the electrical contact 101 is open or the fuse is triggered, the oscillator circuit can oscillate. In this way, the state of the (fusible) fuse can be monitored, among other things. The filter element can have an ohmic resistance in the kOhm range, for example.

[0130] Figure 6 A schematic diagram showing one embodiment of the contact monitoring device 100 is shown. In contrast to the embodiment shown in Figure 5 , a damping element 611 is provided, which is connected downstream of the contact 101, which can be designed as a switch.

[0131] The damping element 611 comprises a circuit with a ferrite 401, which causes signal damping.

[0132] An LC series oscillation loop with an inductance 603 and a capacitance 605 is connected downstream of the ferrite 401. The LC series oscillation loop is provided for forming a low impedance at the oscillation frequency, whereby the contact monitoring signal at the terminal can be minimized or reduced.

[0133] In one embodiment, the inductance 603 can also be omitted.

[0134] In one embodiment, the damping element 611 can be integrated in the filter module 211.

[0135] The damping element 611 corresponds to the damping element 111 in terms of functionality. In addition, the damping element 611 can have filter properties due to the LC oscillation loop, so that in one embodiment a filter is formed.

[0136] Embodiments are explained below for a temperature-compensated contact monitoring device. Figure 7 A basic block diagram of a contact monitoring device 100 with temperature compensation according to the application is shown. The contact monitoring device 100 comprises an oscillator circuit consisting of an amplifier RV and a frequency selection network FSN. A damping element DEL acts on the frequency selection network FSN. The effective damping is determined by the state of the contact 101 to be monitored. The amplifier RV can have a gain that depends on the temperature θ and the operating point k of the amplifier. In general, the temperature influences can lead to a change in the transistor current as a function of the temperature change, so that a change in the gain occurs. This poses a problem, which will be explained in more detail below.

[0137] First, the functional principle of the contact monitoring device 100 is explained again, see Figure 8 . In Figure 8 , the signal from Figure 7The circuit diagram of the frequency selective network FSN is shown. The state of the contact 101 to be monitored (e.g., whether the contact is closed or not) can affect the damping of the damping element DEL of the frequency selective network FSN. The damping of the frequency selective network FSN is represented by damping elements or effective resistors 112 and 122, each with different resistance values. The state of the contact 101 to be monitored affects the position of the switch 102 shown, which, depending on the switch position, connects one of the two damping resistors 112 and 122 to the rest of the frequency selective network FSN. The frequency selective network FSN is additionally formed by connecting an inductor 105 and a capacitor 103 in parallel. The oscillator circuit can be designed for the operating point k such that the gain V of the amplifier RV compensates for the small damping 112 for the first state, and an oscillating input signal a can be observed at input 114 or an oscillating output signal V*a can be observed at output 115. Simultaneously, the oscillator circuit can be designed such that when the switch contact 102 is in the second state, a larger damping 122 takes effect. The effect is that there is no oscillating output signal V*a at input terminal 114 and output terminal 115.

[0138] As is well known, an oscillating circuit must meet certain oscillation conditions to produce stable oscillations. These conditions are clearly defined as follows:

[0139] • The loop gain must be greater than or equal to 1 for stable oscillation.

[0140] • At this frequency, the phase shift of the feedback loop must be an integer multiple of 360°.

[0141] This is precisely what is used in contact monitoring devices. In one switching state of the switch contact, the oscillation condition is met; in the other switching state of the switch contact, the oscillation circuit is damped, and stable oscillation will not occur (the gain of the oscillator is insufficient to compensate for the loss caused by damping).

[0142] Now we will combine Figure 9 Explain these issues. Figure 9 The impedance curve (frequency response) of the parallel resonant circuit is shown. If the switch contact to be monitored is now switched to a low-damped state, the oscillator of the contact monitoring device oscillates at a resonant frequency of approximately 50.2 MHz, and the impedance curve is shown in impedance frequency response 305, see point 305a. On the other hand, if the switch contact is switched to a high-damped state, the oscillator of the contact monitoring device follows the impedance curve shown in impedance frequency response 303, see point 303a. In this strongly damped state 303, stable oscillation will not occur. The oscillation limit 301 depends on the specific circuit and amplifier components and should be as close as possible to the middle of the two curves to ensure that the oscillator oscillates reliably or does not oscillate reliably depending on the contact state.

[0143] This desired behavior of the oscillator circuit can be disturbed by temperature changes. In particular, the amplifier RV exhibits a temperature-dependent behavior. This is because the gain factor of the amplifier RV depends on the temperature. This applies in particular to transistor amplifiers, since the intrinsic conductivity of the semiconductor material and thus the transistor current changes with the temperature. This can destroy the desired behavior of the oscillator circuit and even lead to malfunctions, in which an oscillation signal occurs at the output 115 in both cases of active damping 112 and 122 in one temperature range and / or in both cases of active damping 112 and 122 no oscillation signal occurs on the output 115 in another temperature range, so that it is no longer possible to reliably distinguish the states by means of the contact monitoring device.

[0144] In an expansion of the application, the temperature dependence of the oscillator circuit is compensated by shifting the operating point of the amplifier RV as a function of the temperature, i.e. k -> k(0), so that the gain of the amplifier RV has a negligible temperature dependence or is completely temperature-independent.

[0145] Figure 9 The impedance frequency response from the frequency selection network FSN of Figure 8 is shown. Depending on whether the damping resistor 112 or 122 is active, different impedance curves 303 or 305 are produced. An explanation of the impedance curves has already been explained in connection with the description of Figure 3 At the resonance frequency at point 305a, a resonance occurs in the case of the impedance curve 305 and an oscillation signal occurs at the input 114 and the output 115. At the resonance frequency at point 303a, there is no resonance oscillation in the case of the impedance curve 303 and no oscillation signal occurs at the input 114 and the output 115.

[0146] Figure 10 A more detailed circuit diagram of an exemplary implementation form of an oscillator circuit with temperature compensation according to the application is shown. Identical reference signs denote the same components as in the previous figures. The amplifier RV is here formed by a junction field effect transistor (JFET) 141 in the gate circuit, resistors 144, 146 and 143 and a capacitor 142, by means of which the operating point of the transistor 141 is set. The frequency selection network FSN consists of the inductance 105, the capacitor element 139 formed by the capacitances 139-1 and 139-2 and the damping element DEL consisting of the active resistors 112, 122 and the contact to be monitored 101, the state of which determines the effect of one or the other damping resistor 112, 122. The capacitor 159 stabilizes the operating voltage. The circuit can be designed such that for the first active damping via the damping resistor 112 an oscillation signal can be observed at the output 115 and this oscillation signal is not present when the active damping is carried out via the damping resistor 122.

[0147] According to the application, the operating point of the transistor 141 is influenced by a voltage divider consisting of the thermistor 146 and the resistor 144, so that the gain of the transistor 141 is (almost) independent of temperature or negligible. Resistors that are dependent on temperature can be used as thermistors. There are so-called positive temperature coefficient thermistors. These are, for example, PTC resistors (English: Positive Temperature Coefficient Resistor), whose resistance value increases with increasing temperature. There are also so-called negative temperature coefficient thermistors, NTC resistors (English: Negative Temperature Coefficient Resistor), whose resistance decreases with increasing temperature. In addition, other components with a temperature-dependent behavior, such as semiconductor diodes, can also be used as negative temperature coefficient thermistors in the off direction (not shown).

[0148] The operating point voltage U ap is derived from the supply voltage Vcc and the temperature-dependent voltage division ratio of the resistors 146 and 144. The operating point voltage U ap is derived from the following equation:

[0149] U ap = Vcc * R144 / (R146(0) + R144).

[0150] In this case, U ap refers to the operating point voltage at point 114, Vcc refers to the supply voltage, and 0 refers to the temperature.

[0151] By suitable design of the resistors 144 and 146, the operating point voltage increases (or decreases) with increasing temperature to such an extent that the influence of the temperature-dependent gain is compensated as far as possible by the gain that depends on the operating point. In other words, a temperature-dependent bias voltage is applied to the gate of the transistor 141, so that the gain factor V is as independent of temperature as possible. Thereby a gain that is largely independent of temperature can be achieved, so that a temperature-independent oscillation limit is achieved. The capacitor 142 is optional and can be used, for example, to smooth the operating point voltage. The optimum combination of the resistors 144, 146 and the capacitor 142 can be determined, for example, by experiment.

[0152] Figure 11 Another type of temperature compensation is shown. In this variant, the operating point of the transistor 141 is also stabilized. This solution corresponds to a digital implementation of the operating point stabilization. Here, the operating point voltage U ap is generated digitally and provided directly in a temperature-compensated manner. For this purpose, the temperature 0 needs to be measured. A temperature sensor is therefore required. This is Figure 11The temperature sensor 161 is connected to a microcontroller. The temperature- operating point table 245 is stored in the microcontroller 200. The measured temperature value is indicated to the temperature- operating point table 245. The information of the relevant pulse width modulated signal is obtained from the temperature- operating point table 245. The microcontroller 200 generates the relevant pulse width modulated signal and outputs it via one of its general purpose input / output terminals GPIO. This is fed at point 114 to the contact monitoring device 100. The pulse width of the signal is modulated in accordance with the temperature. In order to generate a temperature-compensated operating point voltage U ap from this, the mean value of the signal in relation to the pulse / pause must be formed. This is done in the circuit shown in Figure 11 by the resistor 148 and the capacitor 142, which together form a low-pass filter. The low-pass filter is connected between the feed point 114 and the transistor 141.

[0153] With this solution, other influences can also be compensated in addition to the temperature, such as ageing, component tolerances, supply voltage fluctuations, etc. The solution can also be used to calibrate the products produced after the manufacturing process. Component tolerances and manufacturing deviations can make product calibration necessary.

[0154] The circuit diagram of the temperature compensation circuit is shown in Figure 1 the circuit shown in the embodiment Figure 1 is shown in Figure 12 , in which temperature compensation is carried out using a negative temperature coefficient thermistor 146. The temperature-dependent voltage divider consisting of the NTC resistor 146 and the resistor 144 provides a gate voltage of U ap = Vcc * R144 / (R146(0) + R144), which is smoothed with the aid of the capacitor 142. By appropriately dimensioning the components, the temperature-dependent gate voltage ensures that the gain of the transistor 141 is as independent of temperature as possible.

[0155] It should be appreciated that the proposed method and related apparatus can be implemented in various forms of hardware, software, firmware, a dedicated processor, or a combination thereof. In a preferred variant, a microcontroller with integrated RAM memory and integrated I / O interface is used. The dedicated processor can comprise an application specific integrated circuit (ASIC), a reduced instruction set computer (RISC) and / or a field programmable gate array (FPGA). Preferably, the proposed method and apparatus are implemented as a combination of hardware and software. The software is preferably installed as an application on a program storage device. This is typically a computer platform based machine which comprises hardware such as one or more central processing units (CPU), random access memory (RAM) and one or more input / output (I / O) interfaces. An operating system is also typically installed on the computer platform. The various processes and functions illustrated herein can be part of the application or can be parts run through the operating system.

[0156] The present disclosure is not limited to the embodiments described herein. There is also room for various adaptations and modifications by the skilled person on the basis of his / her expertise and insofar as they pertain to the present disclosure.

[0157] Legend of the figures

[0158] 100 contact monitoring device

[0159] 101 electrical contact

[0160] 102 switch contact

[0161] 103 oscillator circuit

[0162] 105 coupling element

[0163] 107 signal input

[0164] 109 signal output

[0165] 111 damping element

[0166] 112 first effective resistance

[0167] 113 detector

[0168] 114 feed point

[0169] 115 detector output

[0170] 117 transformer

[0171] 119-1 first inductance

[0172] 119-2 second inductance

[0173] 121 impedance circuit

[0174] 122 second effective resistance

[0175] 123-1 first filter element

[0176] 123-2 second filter element

[0177] 125-1 first output terminal

[0178] 125-2 second output terminal

[0179] 127 switching element

[0180] 129 resistance

[0181] 131 capacitance

[0182] 133 inductance

[0183] 135-1 capacitance

[0184] 135-2 capacitance

[0185] 137-1 capacitance

[0186] 137-2 capacitance

[0187] 139 capacitance element

[0188] 139-1 capacitance

[0189] 139-2 capacitance

[0190] 141 transistor

[0191] 142 capacitor

[0192] 143 resistance

[0193] 144 resistance

[0194] 145 capacitance

[0195] 146 negative temperature coefficient thermistor

[0196] 147-1 diode

[0197] 147-2 diode

[0198] 149 resistance

[0199] 151 transistor

[0200] 153 capacitance

[0201] 155 pull-up resistance

[0202] 157 supply voltage terminal

[0203] 159 smoothing capacitor

[0204] 161 output signal terminal

[0205] 201 switch module

[0206] 203 switch module base

[0207] 205-1 switch contact terminal

[0208] 205-2 switch contact terminal

[0209] 205-3 switch contact terminal

[0210] 207-1 plug-in contact

[0211] 207-2 plug-in contact

[0212] 207-3 plug-in contact

[0213] 209 feed-through terminal

[0214] 211 filter module

[0215] 213 rectifier

[0216] 215-1 first switch control terminal

[0217] 215-2 second switch control terminal

[0218] 217-1 first switch signal output

[0219] 217-2 second switch signal output

[0220] 219-1 first switch connection plug

[0221] 219-2 second switch connection plug

[0222] 221-1 first load terminal

[0223] 221-2 second load terminal

[0224] 223 load voltage source

[0225] 225 electrical load

[0226] 227 conductor bridge

[0227] 229 dividing line

[0228] 240 microcontroller

[0229] 245 temperature-operation point table

[0230] 301 resistance limit value

[0231] 303 first impedance curve

[0232] 303a first resonance frequency point

[0233] 305 second impedance curve

[0234] 305a second resonance frequency point

[0235] 401 ferrite

[0236] 611 damping element

[0237] 601 inductance

[0238] 603 capacitance

[0239] DEL damping element

[0240] FSN frequency selective network

[0241] RV resonance amplifier

Claims

1. Contact monitoring device (100) for monitoring an electrical contact (101) having a first contact state and a second contact state, wherein the contact monitoring device (100) has the following features: an oscillator circuit (103) designed to generate an excitation signal, a coupling element (105) having a signal input (107) and a signal output (109), wherein the oscillator circuit (103) is connected upstream of the signal input (107) to apply the excitation signal to the coupling element (105), wherein the coupling element (105) is designed to convert the excitation signal into a contact monitoring signal and to output the contact monitoring signal to the signal output (109) for application to the electrical contact (101), wherein a first impedance value is set on the oscillator circuit (103) when the electrical contact (101) is in the first contact state and a second impedance value is set on the oscillator circuit (103) when the electrical contact (101) is in the second contact state, wherein the oscillator circuit (103) is designed to generate a resonant oscillation and output the excitation signal when the electrical contact (101) is in the first contact state and has the first impedance value, wherein the oscillator circuit (103) has means for thermal stabilization of the oscillator circuit (103), wherein the oscillator circuit (103) has an oscillation loop with a feedback branch and an amplifier (RV), wherein the amplifier (RV) amplifies a signal fed back by the feedback branch, wherein the amplifier (RV) has at least one transistor (141) whose operating point can be set, wherein the gain of the at least one transistor (141) is stabilized by matching the operating point using the means for thermal stabilization; and a detector (113) designed to detect the type of excitation signal in order to monitor the electrical contact (101).

2. Contact monitoring device (100) according to claim 1, wherein the contact monitoring device (100) is designed to prevent the formation of a resonant oscillation in the second contact state, thereby preventing the generation of an excitation signal or the generation of a further resonant oscillation and the output of a further excitation signal, and wherein the detector (113) is designed to detect the type of the first excitation signal and the type of the further excitation signal or the type of the first excitation signal and the absence of the first excitation signal in order to detect the electrical contact state.

3. Contact monitoring device (100) according to claim 1, wherein the operating point of the transistor (141) can be set by a voltage divider, wherein a thermistor (146), or other negative temperature coefficient thermistor or positive temperature coefficient thermistor, is used as an element of the voltage divider as means for thermal stabilization.

4. The contact monitoring device (100) according to claim 3, wherein the thermistor (146) is an NTC or PTC resistor.

5. Contact monitoring device (100) according to claim 1, wherein a temperature sensor (161) is used as a means for thermal stabilization, whose signal is analyzed by a microcontroller (240), which generates a corresponding correction signal, which sets the operating point of at least one transistor (141) for thermal stabilization.

6. Contact monitoring device (100) according to claim 5, wherein the microcontroller (240) generates a PWM signal, a correction signal in the form of a pulse width modulated signal, and an averaging means averages the PWM signal and supplies it to the transistor (141).

7. Contact monitoring device (100) according to claim 6, wherein the averaging means is formed in the form of a low-pass filter consisting of a resistor (148) and a capacitor (142).

8. Contact monitoring device (100) according to claim 1, wherein the oscillator circuit (103) is designed to generate an excitation signal with an excitation frequency corresponding to the resonance frequency of the oscillator circuit (103) using a first impedance value, and wherein the oscillator circuit (103) is further designed to change the signal amplitude of the excitation signal based on the impedance value at the signal input (107).

9. Contact monitoring device (100) according to claim 1, wherein the contact monitoring device has a damping element (111, 611) connected downstream of the signal output (109) and coupled to the electrical contact (101), wherein the damping element (111, 611) is designed to provide an impedance when the electrical contact (101) is in the second contact state, thereby preventing the effect of the impedance of the electrical contact (101) in the second contact state, wherein the signal input (107) of the coupling element (105) is damped by the action of the damping element (111, 611) and the oscillator circuit (103) is unable to oscillate and prevents the output of the excitation signal.

10. Contact monitoring device (100) according to claim 9, wherein the coupling element (105) and the oscillator circuit (103) are designed to form an oscillation loop, and wherein the damping element (111) is designed to damp the oscillation loop in the second contact state to reduce the signal amplitude of the excitation signal, and / or wherein the damping element (111, 611) is bridged with low resistance and the damping of the damping element (111, 611) coupled to the signal input (107) by means of the coupling element is reduced when the electrical contact (101) is in the first contact state, and wherein the oscillator circuit (103) is designed to generate an excitation signal with an increased signal amplitude with reduced damping, and / or wherein the damping element (111, 611) comprises a capacitance formed by a printed circuit board capacitor, and / or Further comprising an impedance circuit (121) connected downstream of the signal output (109) and coupled to the damping element (111, 611), wherein the impedance circuit (121) is designed to compensate for a leakage inductance and / or a stray capacitance of the coupling element (105) in the case of a contact monitoring signal having a predetermined frequency.

11. Contact monitoring device (100) according to claim 10, wherein the impedance circuit (121) is designed for minimizing a total capacitance and / or a total inductance on a galvanic isolation of the coupling element (105).

12. Contact monitoring device (100) according to claim 1, wherein the oscillator circuit (103) has a detector output (115) and is designed to provide an excitation signal to a detector (113) via the detector output (115).

13. Contact monitoring device (100) according to claim 1, wherein the detector (113) is designed to convert the excitation signal into an output signal and to output the output signal in at least two different signal states, wherein a first signal state of the at least two signal states indicates a closed electrical contact (101) and a second signal state of the at least two signal states indicates an open electrical contact (101).

14. Contact monitoring device (100) according to claim 13, wherein the detector (113) is designed to output the output signal in the first signal state when an oscillating excitation signal is present at the detector output (115) and to output the output signal in the second signal state when a non-oscillating excitation signal is present at the detector output (115) or when a signal amplitude of the excitation signal is below an amplitude limit value.

15. Contact monitoring device (100) according to claim 1, wherein the coupling element (105) is designed to galvanically isolate the oscillator circuit (103) and / or the detector (113) from the electrical contact (101).

16. Contact monitoring device (100) according to claim 1, wherein the detector (113) is designed to detect a change of the contact signal and the excitation signal for switching the electrical contact (101), and wherein the detector (113) is further designed to output a binary fault signal indicating whether the electrical contact (101) is switched in accordance with the contact signal.

17. Contact monitoring device (100) according to claim 16, wherein the detector (113) is designed to detect the excitation signal within a predetermined time interval after receiving the contact signal in order to determine whether the electrical contact (101) is switched in accordance with the contact signal within the predetermined time interval, and / or Further having an optical display element designed to display a detection of the contact signal and a corresponding detected switching of the electrical contact (101) or a deviation from an expected contact signal.

18. The contact monitoring device (100) according to claim 1, wherein the coupling element (105) comprises a transformer (117) having a first inductance (119-1) and a second inductance (119-2), wherein the first inductance (119-1) and the second inductance (119-2) are inductively coupled in order to convert an excitation signal into a contact monitoring signal.

19. The contact monitoring device (100) according to claim 1, wherein the contact monitoring device has a first filter element (123-1) and a second filter element (123-2), wherein the electrical contact (101) has a first output connection (125-1) downstream of which the first filter element (123-1) is connected, and wherein the electrical contact (101) has a second output connection (125-2) downstream of which the second filter element (123-2) is connected in order to dampen high-frequency signals applied to the electrical contact (101) and / or to an electrical load and / or to a voltage source coupled with the electrical contact (101) by the coupling element (105).

20. The contact monitoring device (100) according to claim 19, wherein the first filter element (123-1) and / or the second filter element (123-2) have an ohmic impedance component at the oscillator frequency which is designed to prevent an external short circuit of the first output connection (125-1) and the second output connection (125-2) from being detected as a closure of the electrical contact (101).

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