Sensor circuit, sensor module and installation with energy-consuming components

Abstract

The utility model relates to a sensor circuit (20), the sensor circuit (20) comprises a sensor unit (21), an amplifier unit (22) and an ADC module (23), the sensor unit (21) is connected with the input end of the amplifier unit (22), the output end of the amplifier unit (22) is connected with the input end of the ADC module (23), the sensor circuit (20) additionally comprises a current limiter (24), and the current limiter (24) is connected with the ADC module (23). The current limiter (24) limits the output current of the amplifier unit (22). In addition, the utility model relates to a sensor module and a facility with an energy-consuming component.

Description

Technical Field

[0001] The utility model relates to a sensor circuit, a sensor module and a facility with a plurality of sensor circuits. Background Art

[0002] Sensors are used to automatically measure the parameters of a facility. Usually, the sensor cannot be used alone for this purpose, but it must be integrated into a sensor circuit. Typically, the sensor circuit includes a sensor unit that outputs a signal, a signal amplifier that amplifies the signal of the sensor unit, and an ADC module (ADC: Analog-Digital-Converter) that outputs the amplified signal as a digital value. Typical signals are voltage or current, which can be constant or pulsed. Voltage can be converted into current by means of an ohmic resistor, and vice versa.

[0003] The preferred signal amplifier includes an operational amplifier circuit, the signal is input at the input terminal of the operational amplifier circuit, and is amplified and provided to the ADC module by the output terminal of the operational amplifier circuit. Typically, one input terminal of the operational amplifier is used as a reference, such as GND, and the other input terminal is used as a signal input terminal or to measure a voltage difference at a sensor.

[0004] Sometimes high demands are made on sensor circuits, not only in terms of their accuracy, but also in terms of their insensitivity to external influences.

[0005] For example, in MRT systems, gradient coils are monitored, in particular, by means of temperature sensors. The sensor unit can be, for example, a thermistor or a temperature-sensitive ohmic resistor, which is in thermal contact with the gradient coil and whose voltage curve allows the temperature of the gradient coil to be inferred. In the case of a temperature-sensitive resistor, for example, the voltage drop across the resistor can be amplified by two inputs of a signal amplifier, and the amplified voltage can be forwarded to an ADC module.

[0006] Typically, gradient coils are monitored by means of a plurality of sensors at different locations of the coils. In this case, it is entirely possible that, due to fluctuations in the magnetic field or damage to the insulation of the coils, high voltages are applied to the signal amplifier, which are then further amplified. The resulting high currents can damage the ADC module.

[0007] In order not to damage the ADC module, the ADC module usually has a protection diode through which an excessively high current can flow out. However, if an excessively large current flows through the protection diode, the protection diode may be damaged, which may cause damage to the entire ADC module.

[0008] In order to relieve the load on the ADC module or its protection diode, an ohmic resistor is connected in series between the output of the signal amplifier and the input of the ADC module. The resistor can have a resistance value in the kilo-ohm range.

[0009] A major disadvantage of this solution is that the resistance causes measurement errors which reduce the quality of the measurement. Utility Model Content

[0010] The object of the present invention is to provide an alternative sensor circuit, by means of which the above-mentioned disadvantages are avoided and measurement errors are reduced, in particular while optimally protecting the ADC module.

[0011] This object is achieved by a sensor circuit according to the invention, by a sensor module according to the invention and by an arrangement according to the invention, which can in any case be a magnetic resonance tomography system.

[0012] The sensor circuit according to the present invention comprises a sensor unit, an amplifier unit and an ADC module, wherein the sensor unit is connected to the input end of the amplifier unit, and the output end of the amplifier unit is connected to the input end of the ADC module, wherein the sensor circuit additionally comprises a current limiter which limits the output current of the amplifier unit.

[0013] Sensor units are known to the person skilled in the art. This refers to electrical or electronic components which can generate electrical signals in the form of current and / or voltage depending on environmental parameters, such as temperature, humidity, magnetic field, brightness, sound intensity or general field intensity. The signals are usually so small that direct conversion by means of an ADC module is problematic. An example of a sensor unit is a thermistor, the resistance of which is dependent on its temperature.

[0014] Amplifier units are also known to those skilled in the art. The amplifier unit has at least one input terminal, into which a current to be amplified or a voltage to be amplified is input, and at least one output terminal, from which the amplified current or the amplified voltage is output. An operational amplifier circuit is usually used as an amplifier unit. An operational amplifier circuit typically has two input terminals and one output terminal.

[0015] For a better overview, "signal" is also mentioned below. A signal is a voltage or a current (it can also be both, for example in the form of power). A signal can be continuous, for example an applied voltage (which increases, decreases or remains constant depending on the measurement), but it can also be pulsed. For a better distinction, the signal of the sensor unit is called "sensor signal" (it can also be called "input signal" because it enters the amplifier unit), and the amplified signal is called "output signal" because it is the signal leaving the amplifier unit.

[0016] The sensor unit is connected to an input of the amplifier unit so that the sensor signal can enter the amplifier, be amplified there and leave the amplifier as an output signal. The ADC module is connected to an output of the amplifier unit so that the output signal enters the ADC and can be converted into a digital value there. For example, in such a series circuit, the voltage of the sensor unit amplified by the amplifier unit is applied to the input of the ADC module.

[0017] In order to protect the ADC module, the sensor circuit additionally comprises a current limiter. The current limiter is connected such that it limits the output current of the amplifier unit. This is preferably achieved via limiting the input current, but the current limiter can also directly limit the output current of the amplifier unit. As a result, a series circuit of the amplifier unit, the resistor and the ADC module is no longer required, because the current output from the amplifier unit is already limited.

[0018] Due to the current limitation of the amplifier unit, the resistor between the amplifier unit and the ADC module can be omitted. The advantage of omitting the resistor can be illustrated by the following calculation. There, in order to express the "counting step size" of the ADC module ” or resolution, using the abbreviation “LSB” (“Least Significant Bit”, i.e. the lowest value bit 0 / 1) for ADC, which indicates the lowest count unit of the ADC module.

[0019] It should be noted that ADC modules usually measure current internally, wherein a voltage is applied externally and converted into a current via a resistor. However, for technical reasons, part of the current is not available for measurement and is referred to as the "quiescent current" or "bias current". The quiescent current, which is usually not constant and is individualized for each sensor circuit when using multiple sensor circuits, causes measurement errors.

[0020] In the case of a 12-bit ADC module with a measurement range of 2000 mV, the count unit corresponds to 1 LSB = 2000 mV / 4096 = 0.488 mV. Therefore, the value of the output of the ADC module increases by one count every approximately 0.5 mV. For a calculation example it is assumed that a voltage of 14 V is used as the input voltage for the sensor circuit, the ADC module has a quiescent current of 0.02 mA, the ADC value "0" corresponds to 0° C., and the value "4096" corresponds to 300° C. The protection diode should be able to withstand a maximum current of 2 mA.

[0021] In order for the current flowing through the ADC module (in the case of a measuring range of 2V) to be no more than 2mA at 14V, a resistor of 12V / 2mA=6kOhm (14V-2V=12V) is required in the series circuit between the amplifier unit and the ADC module. However, with a quiescent current of 0.02mA, the 6kOhm resistor causes an error voltage of 0.02mA×6kOhm=120mV. Here, it should be noted that, firstly, the quiescent current does not necessarily have to be constant, and secondly, the quiescent current may be different for different sensor circuits. Therefore, it can be assumed that the error voltage can be anywhere between 0V and 120mV. If the sensitivity of the ADC module of 1LSB=about 0.5mV calculated above is observed, 120mV corresponds to approximately 240LSB. Assuming that 4096 counts correspond to 300°C in the ADC module, the value of 240 corresponds to approximately 18°C. Therefore, with the help of a 6kOhm resistor, a measurement error of about 18°C ​​through the quiescent current is possible.

[0022] Omitting the resistor can significantly reduce the measurement error. However, if there is no resistor between the amplifier unit and the ADC module, the gain of the amplifier unit must be adjusted so that, in the case of a (determined) maximum sensor signal, the voltage of the output signal corresponds to the maximum voltage of the measuring range of the ADC module. Thus, in the above example, in the case of a sensor signal for 300° C., the voltage of the output signal should correspond to 2000 mV of the measuring range.

[0023] In terms of the voltage applied by the output signal at the ADC module, the amplifier unit can be operated with a voltage corresponding to the maximum voltage of the measuring range. The current limiter then ensures that the maximum current of the output signal is limited. However, this is impractical for some circuits. Typically, such sensor circuits are operated with a voltage higher than the maximum voltage of the measuring range of the ADC module.

[0024] Preferably, the gain of the amplifier unit is designed such that, given a preset maximum voltage UA of the output signal and a maximum voltage UM of the measuring range preset by the ADC module, the gain of the amplifier unit is UM / UA. It should be noted that the preset maximum voltage of the output signal corresponds in particular to the supply voltage of the amplifier unit, which ensures particular safety.

[0025] The sensor module according to the present invention comprises a plurality of sensor circuits according to the present invention. The sensor module preferably comprises more than 5 sensor circuits, particularly preferably more than 10 sensor circuits, in particular more than 50 sensor circuits. The sensor circuit preferably comprises a temperature sensor as a sensor unit.

[0026] The installation according to the present invention having an energy-consuming component comprises a plurality of sensor circuits according to the present invention, in particular a plurality of sensor modules according to the present invention. The installation is preferably a magnetic resonance tomography system and comprises gradient coils. It is preferred that a plurality of sensor circuits, in particular a plurality of sensor circuits of a sensor module, monitor at least one magnet coil, in particular a gradient coil. It is particularly preferred that during the monitoring, the temperature of the magnet coil is monitored by means of a temperature sensor.

[0027] The magnetic resonance tomography system according to the present invention comprises the sensor circuit according to the present invention.

[0028] Other particularly advantageous designs and improvements of the present invention can be derived from the following description, in which embodiments of one embodiment category can also be improved similarly to embodiments and description parts of another embodiment category, and in particular, individual features of different embodiments or variants can also be combined into new embodiments or variants.

[0029] According to a preferred sensor circuit, the current limiter is arranged in a series circuit between the energy supply unit of the amplifier unit and the amplifier unit and limits the energy supply of the amplifier unit. Preferably, the current limiter is arranged upstream of the positive supply terminal of the amplifier unit. Alternatively, the current limiter can also be arranged between the negative supply terminal and GND (i.e. ground or negative pole).

[0030] According to a preferred sensor circuit, the current limiter is arranged in such a way that it limits the input current of the energy supply of the amplifier unit.

[0031] According to a preferred sensor circuit, the current limiter is part of the amplifier unit and limits the output current output at the output (of the amplifier unit), ie the current of the output signal.

[0032] According to a preferred sensor circuit, the amplifier unit is an operational amplifier circuit, which preferably has a reverse-coupled operational amplifier, wherein a portion of the output voltage is fed back from the output of the operational amplifier to one of the inputs. The amplifier unit is preferably a comparator or a differential amplifier.

[0033] According to a preferred sensor circuit, the gain of the amplifier unit is set such that, with a predefined maximum input voltage UE and a maximum voltage UM of the measuring range predefined by the ADC module, the gain of the amplifier unit is less than or equal to UM / UE.

[0034] According to a preferred sensor circuit, the sensor unit comprises a temperature sensor, such as a thermal resistor or a thermistor.

[0035] In principle, current limiters are known in the prior art. In order to implement the utility model, a current limiter, such as an ohmic resistor, can be used in the known current limiters to limit the current to the ADC module. According to a preferred sensor circuit, a current limiter formed by at least two transistors is used. In a preferred transistor circuit, two NPN transistors are used, wherein the collector and the base of the first transistor are connected to the positive voltage input via a first resistor (especially having a value between 1kOhm and 100kOhm), and the emitter of the first transistor is connected to the voltage input (of the energy supply) of the amplifier unit via a second resistor (especially having a value between 10Ohm and 200Ohm). The emitter of the second transistor is connected to the base of the first transistor (and also connected to the positive voltage input via the first resistor upstream of the base of the first transistor). The base of the second transistor is connected to the emitter of the first transistor (and also connected to the input of the energy supply of the amplifier unit via the second resistor downstream of the emitter). The collector of the second transistor is connected to the input of the energy supply of the amplifier unit. Therefore, the second resistor is located between the base and the collector of the second transistor. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention will be described in detail again according to the embodiments with reference to the accompanying drawings. In the different drawings, the same components are provided with the same reference numerals. The drawings are generally not to scale. The drawings show:

[0037] Figure 1 A schematic diagram showing a magnetic resonance tomography system having an embodiment of the present invention is shown,

[0038] FIG. 2 shows a sensor circuit according to the prior art,

[0039] Figure 3 An example of a sensor circuit according to the present invention is shown.

[0040] Figure 4 An example of a sensor module according to the present invention is shown. DETAILED DESCRIPTION

[0041] In the following figures, only the elements that are important for the invention or are helpful for understanding it are drawn. Thus, for example, slice selection gradients are not shown, although they may well be present in the pulse sequence.

[0042] exist Figure 1 1 shows a roughly schematic diagram of a magnetic resonance tomography system 1. On the one hand, the magnetic resonance tomography system comprises an actual magnetic resonance scanner 2 with an examination space 3 or a patient tunnel, in which a patient or an examinee is positioned on a bed 8, and in whose body an actual examination object O is located.

[0043] The magnetic resonance scanner 2 is usually equipped with a basic magnetic field system 4, a gradient system 6 and an HF transmission antenna system 5 and an HF reception antenna system 7. The basic magnetic field system 4 is designed in a conventional manner in such a way that it generates a basic magnetic field in the longitudinal direction of the patient, that is, along the longitudinal axis of the magnetic resonance scanner 2 extending in the z direction. The gradient system 6 usually includes individually controllable gradient coils so that gradients can be switched independently of one another in the x-direction, the y-direction or the z-direction.

[0044] The magnetic resonance tomography system 1 also has a central control device 13 for controlling the MR system 1 and also for evaluating sensor signals. The central control device 13 includes a sequence control unit 14. The sequence control unit 14 controls the sequence of radio frequency pulses (HF pulses) and gradient pulses within a measurement session according to a selected pulse sequence for recording a volume region of interest of the examination object. In order to output the individual HF pulses of the pulse sequence, the central control device 13 has a radio frequency transmission device 15, which generates, amplifies and feeds the HF pulses into the HF transmission antenna system 5.

[0045] In order to control the gradient coils of the gradient system 6 so as to switch the gradient pulses appropriately according to the preset pulse sequence, the control device 13 has a gradient system interface 16. Diffusion gradient pulses and spoiler gradient pulses can be applied via the gradient system interface 16. The sequence control unit 14 communicates with the radio frequency transmission device 15 and the gradient system interface 16 in a suitable manner, for example by sending sequence control data SD, to execute the pulse sequence.

[0046] The control device 13 also has a radio frequency receiving device 17 (which likewise communicates in a suitable manner with the sequence control unit 14 ) in order to receive magnetic resonance signals in a coordinated manner within a readout window predefined by the pulse sequence by means of the HF receiving antenna system 7 in order to acquire raw data.

[0047] The reconstruction unit 18 receives the acquired raw data and reconstructs magnetic resonance image data therefrom. This reconstruction is usually also performed based on parameters that can be predefined in the corresponding measurement or control protocol. The image data can then be stored in a memory 19, for example.

[0048] The details of how suitable raw data can be acquired by irradiation of RF pulses and switching of gradient pulses and how MR images or parameter maps can be reconstructed therefrom are known in principle to a person skilled in the art and are therefore not explained in detail here.

[0049] Here, a sensor module 12 is shown on the gradient system 6, which measures the temperature of the gradient coils of the gradient system 6. The measurement results of the sensor module 12 can be evaluated by means of a central control device 13 and, if necessary, control commands can be output based on the measurements of the sensor module 12. For example, the measurement can be interrupted if the temperature of the gradient system 6 is too high.

[0050] The central control device 13 can be operated or the measurements of the sensor modules 12 can be output via a terminal 11 having an input unit 10 and a display unit 9, so that the entire magnetic resonance tomography system 1 can also be operated by an operator via the terminal 11. Magnetic resonance tomography images and measured values ​​can also be displayed on the display unit 9, and measurements can be planned and started by means of the input unit 10, if necessary in conjunction with the display unit 9, and in particular control protocols can be selected and modified if necessary.

[0051] FIG. 2 shows a sensor circuit 20 with a temperature sensor S according to the prior art. The voltage dropped to the sensor S is amplified by an operational amplifier V, which is connected to a resistor R as a differential amplifier. The maximum voltage of the output signal is here in the order of magnitude of the voltage preset by the energy supply device P. The current and voltage at the input of ADC A are adjusted via the resistor R between the operational amplifier V and ADC A. For example, if the maximum current is 2 mA and the maximum detectable voltage is 2 V, then in the case of a supply voltage of 14 V via the energy supply device P, 12 V must be dropped at the resistor at a current of 2 mA. Therefore, a 6 kOhm resistor should be used.

[0052] If, for example, there is now an excessively high voltage at the sensor S, which is indicated by the jagged arrow, then at the output of the operational amplifier V there is an output signal which corresponds, for example, to a supply voltage of 14 V. The resistor R between the operational amplifier V and the ADC A then protects the ADC A. If there is an overvoltage at the input of the ADC, a current can flow through the protective diode D, but only in small amounts. This current can be influenced by a suitable choice of the resistor R (for example, 6 kOhm).

[0053] Due to the resistor R between the operational amplifier V and ADC A and the quiescent current flowing there, a voltage is permanently present at the input of ADC A. This voltage falsifies the measurement result.

[0054] Figure 3 An example of a sensor circuit according to the present invention is shown. The sensor circuit is constructed similarly to the circuit in FIG2 , but differs in two important aspects.

[0055] The sensor circuit 20 comprises a sensor unit 21, an amplifier unit 22 and an ADC module 23. It can be seen that the sensor unit 21 is connected to the input of the amplifier unit 22, and the output of the amplifier unit 22 (operational amplifier V) is connected to the input of the ADC module 23. The amplifier unit 22 is an operational amplifier circuit 22 having an operational amplifier V coupled inversely in a differential amplifier circuit. As the sensor unit 21, a temperature sensor S is shown, whose temperature-dependent resistance is input as a voltage difference into the two inputs of the operational amplifier V. The output signal of the amplifier unit 22 is then an amplified voltage signal of the temperature sensor S.

[0056] and Figure 1 Differently, the sensor circuit 20 comprises a current limiter 24 which limits the output current of the amplifier unit 22. The current limiter 24 is arranged upstream of the positive supply terminal thereof in a series circuit between the energy supply unit P and the amplifier unit 22 and limits the input current of the amplifier unit 22. Thus, the output current is limited by limiting the energy that can be provided for amplification.

[0057] As a second difference, the resistor between the amplifier unit 22 and the ADC module 23 is omitted, since it is no longer needed to limit the current. As a result, the quiescent current at the input of the ADC module 23 no longer causes a voltage measured at the ADC module (due to the resistor) and thus no longer causes measurement errors.

[0058] In the case where the amplifier unit 22 is to be operated with a voltage above the measuring range of the ADC module (which is usually the case), the gain of the amplifier unit 22 should be set so that, with a preset maximum input voltage UE (which is usually also the maximum voltage of the output signal) and a maximum voltage UM of the measuring range preset by the ADC module, the gain is less than or equal to UM / UE. If the measuring range of the ADC module 23 is 2 volts and the supply voltage of the amplifier unit 22 is fifteen volts, the two resistors R between the sensor unit 21 and the amplifier unit 22 can be dimensioned at, for example, 300 kOhm, and the resistor R between the input of the operational amplifier V and GND and the resistor R of the feedback can each have a value of 40 kOhm. Since the gain of the differential amplifier is given by the ratio of the resistors R, the maximum voltage at the ADC module is 15 V×40 / 300=2 V. With the current limitation to 2 mV, the ADC module is not in danger at any time if its protection diode D can withstand the current.

[0059] Figure 4 An example of a sensor module 12 according to the present invention is shown, and the sensor module 12 generally has a sensor module 12 such as can be used in Figure 3 2. The sensor circuits 20 are shown in FIG. 2. The sensor circuits each include a sensor unit 21, an amplifier unit 22, and an ADC module 23. The amplifier unit 22 of each sensor circuit 20 additionally includes a current limiter 24, which limits the output current of the amplifier unit 22. The sensor unit 21 may have a temperature sensor S, for example.

[0060] Finally, it is pointed out again that the drawings described in detail above are only embodiments, and those skilled in the art can modify them in completely different ways without departing from the scope of the present invention. In addition, the use of the indefinite article "a" or "an" does not exclude that the relevant features can also exist multiple times. Similarly, the terms "unit" and "device" do not exclude that the components involved can be composed of multiple co-acting sub-components, which can also be spatially distributed if necessary. The term "plurality" should be understood as "at least one". Regardless of the grammatical gender of a particular term, people with male or female gender identity are included.

Claims

1. A sensor circuit (20), the sensor circuit (20) comprising a sensor unit (21), an amplifier unit (22) and an ADC module (23), wherein the sensor unit (21) is connected to an input end of the amplifier unit (22), and an output end of the amplifier unit (22) is connected to an input end of the ADC module (23), It is characterized in that The sensor circuit (20) additionally comprises a current limiter (24) which limits the output current of the amplifier unit (22).

2. The sensor circuit according to claim 1, The current limiter (24) is arranged in a series circuit between an energy supply unit (P) of the amplifier unit (22) and the amplifier unit (22), and the current limiter (24) limits the energy supply of the amplifier unit (22).

3. The sensor circuit according to claim 2, The current limiter (24) is arranged upstream of the positive supply terminal of the amplifier unit (22).

4. The sensor circuit according to any one of claims 1 to 3, The current limiter (24) is arranged in such a way that it limits the input current of the energy supply of the amplifier unit (22).

5. The sensor circuit according to claim 1, The current limiter (24) is a part of the amplifier unit (22) and limits an output current output at the output terminal.

6. The sensor circuit according to any one of claims 1 to 3, The amplifier unit (22) is an operational amplifier circuit.

7. The sensor circuit according to claim 6, The operational amplifier circuit has a reversely coupled operational amplifier (V), wherein a portion of the output voltage is fed back from the output terminal of the operational amplifier (V) to one of the input terminals.

8. The sensor circuit according to claim 6, The amplifier unit (22) is a comparator or a differential amplifier.

9. The sensor circuit according to any one of claims 1 to 3, The gain of the amplifier unit (22) is set such that, in the case of a preset maximum input voltage UE and a maximum voltage UM of a measurement range preset by the ADC module, the gain is less than or equal to UM / UE.

10. The sensor circuit according to any one of claims 1 to 3, The sensor unit (21) comprises a temperature sensor (S).

11. A sensor module (12), It is characterized in that The sensor module (12) comprises a plurality of sensor circuits (20) according to any one of claims 1 to 10.

12. The sensor module (12) according to claim 11, The sensor module (12) has more than ten sensor circuits (20).

13. The sensor module (12) according to claim 11, The sensor circuit (20) has a temperature sensor (S) as a sensor unit (21).

14. A facility having components that consume energy, It is characterized in that The arrangement comprises a plurality of sensor circuits (20) according to any one of claims 1 to 10.

15. The facility according to claim 14, The arrangement comprises a sensor module (12) according to any one of claims 11 to 13.

16. The facility according to claim 14 or 15, The device is a magnetic resonance tomography system (1) and comprises gradient coils (6), wherein a plurality of sensor circuits (20) monitor at least one magnet coil (4, 6).

17. The facility according to claim 16, A plurality of sensor circuits (20) of a sensor module (12) monitor at least one magnet coil (4, 6).

18. The facility according to claim 16, A plurality of sensor circuits (20) monitor the gradient coil (6).

19. The facility according to claim 16, At least a portion of the sensor circuit (20) comprises a temperature sensor (S), and the sensor circuit (20) monitors the temperature of at least one magnet coil (4, 6).

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