Compatibility module for a digital circuit

Abstract

The invention relates to a compatibility module (10) for an electrical circuit (100), comprising: - a module input (11) suitable for being connected to a load output (21) of a load relay (20), - a module output (12) connected to the module input (11), - a reference potential connection (13), - a detector (30) connected to the module input (11) and suitable for detecting a bounce of a load relay (20), - a controllable switch (40) having a switch input (41), a switch output (42) and a switch control input (43), wherein the switch input (41) is connected to the module input (11) and the switch (40) is suitable for being controlled by the detector (30) via the switch control input (43) depending on a detected bounce of a load relay (20), - a load (50) electrically arranged between the switch output (42) and the reference potential terminal (13).

Description

[0001] The invention relates to a compatibility module for a digital circuit, an electrical circuit and a method for using a load relay with a digital circuit.

[0002] In analytical measurement technology, particularly in water management, environmental analysis, industrial applications such as food technology, biotechnology, and pharmaceuticals, as well as for a wide variety of laboratory applications, measured variables such as pH, conductivity, or the concentration of analytes, such as ions or dissolved gases in a gaseous or liquid medium, are of great importance. These measured variables can be recorded and / or monitored using electrochemical sensors, such as optical, potentiometric, amperometric, voltammetric, or coulometric sensors, or conductivity sensors.

[0003] These measured variables are usually processed in a so-called transmitter, for example, to be communicated to a control center. The transmitter supplies the sensor and all associated components, such as cleaning units, with electrical energy. An example of a cleaning unit for an optical sensor is a wiper unit, which regularly cleans the window of the optical sensor to prevent dirt buildup and ensure the highest measurement quality.

[0004] So-called load relays are usually used for this purpose. Load relays that are not explicitly designed for switching small currents (such as small-signal or reed relays) require a minimum current, which is often specified in the load relay's datasheet as a current / voltage combination (e.g., 5V / 100mA, 20V / 25mA). This minimum load current is required to ensure that a sufficiently strong spark is generated when the relay contacts are released, which cleans the relay's contact surfaces. Failure to achieve this minimum load current can prematurely lead to accelerated oxidation and thus to high-resistance relay contacts. This can result in relay malfunction.

[0005] However, circuits used in a PLC environment, for example, must not exceed certain maximum currents. However, the maximum currents specified in a PLC standard for digital inputs are sometimes insufficient to meet the requirements of load relay manufacturers. For this reason, load relays are not used in these environments, but rather special relays that do not have the minimum load current problem described above.

[0006] If a circuit has a digital input that is to be connected to an existing infrastructure with a load relay, the problem may arise that the minimum load current requirements for the load relay are not met, since the digital input typically draws only very low currents. This results in the oxidation described above.

[0007] It is therefore an object of the invention to propose a module which enables compatibility of load relays with digital input circuits.

[0008] This object is achieved according to the invention by a compatibility module for an electrical circuit according to claim 1.

[0009] The compatibility module according to the invention comprises: - a module input suitable for connection to a load output of a load relay, - a module output connected to the module input, - a reference potential connection, - a detector connected to the module input and suitable for detecting a bounce of a load relay, - a controllable switch having a switch input, a switch output and a switch control input, wherein the switch input is connected to the module input and the switch is adapted to be controlled by the detector via the switch control input depending on a detected bounce of a load relay, - a load electrically connected between the switch output and the reference potential terminal.

[0010] The compatibility module according to the invention makes it possible to make a digital input circuit compatible with a load relay. This ensures that the minimum current specified for the load relay is not exceeded. In other words, a digital input of a digital circuit can be operated either at a digital output of another digital circuit or at a load relay without violating the requirements of the load relay manufacturer and still be compatible with digital outputs according to the PLC standard.

[0011] According to one embodiment of the invention, the detector comprises a computing unit and a memory, wherein the computing unit is suitable for detecting and storing a first closing time of a load relay, as well as for detecting and storing a first opening time of the load relay, and for controlling the switch based on the first closing time and the first opening time.

[0012] According to a further embodiment of the invention, the detector comprises a computing unit, and the computing unit is adapted to generate a clock signal and the detector is adapted to control the switch depending on the clock signal.

[0013] According to one embodiment of the invention, the load has an adjustable resistance and the detector is adapted to detect a load current flowing through the load, wherein the detector is connected to the load in such a way as to adjust the adjustable resistance of the load depending on the load current flowing through the load.

[0014] The object described above is further achieved by an electrical circuit for a field device according to claim 5.

[0015] The electrical circuit according to the invention comprises: - a compatibility module according to the invention, - a load relay, with a load output, a load input and a load control connection, - a digital circuit with a digital input, the digital input being connected to the module output, - a voltage source connected to the load input of the load relay, a relay control connected to the load control terminal.

[0016] The object described above is further achieved by a method for using an electrical circuit according to claim 6.

[0017] The method according to the invention comprises: - Providing an electrical circuit according to the invention, - Detecting a bounce of the load relay by the detector, - Switching the switch depending on the bounce detected by the detector.

[0018] According to one embodiment of the invention, the detector comprises a computing unit and a memory, wherein the computing unit detects and stores a first closing time of the load relay and detects and stores a first opening time of the load relay, and controls the switch based on the first closing time and the first opening time.

[0019] According to one embodiment of the invention, the detector comprises a computing unit, and the computing unit generates a clock signal and the detector controls the switch depending on the clock signal.

[0020] According to one embodiment of the invention, the load comprises an adjustable resistor and the detector detects a load current flowing through the load, wherein the detector is connected to the load and adjusts the resistance of the load depending on the load current flowing through the load.

[0021] The invention is explained in more detail with reference to the following description of the figures. They show: - Fig. 1: a schematic representation of an electrical circuit according to the invention with a compatibility module according to the invention, - Fig. 2: a schematic representation of switching cycles of the Fig. 1 used load relays and switches.

[0022] The Fig. The electrical circuit 100 according to the invention shown in Figure 1 comprises a compatibility module 10, a load relay 20, a digital circuit 60, a voltage source 70 and a relay controller 80.

[0023] Thanks to the compatibility module 10, it is achieved that the load relay 20 can be used with the digital circuit 60 and that the minimum required currents in the load relay 20 are not undercut, even though the minimum required current of the load relay 20 is greater than the maximum permissible current of the digital circuit 60.

[0024] The compatibility module 10 comprises a module input 11, a module output 12, a reference potential connection 13, a detector 30, a controllable switch 40 and a load 50.

[0025] In the Fig. In the example shown in Figure 1, the module input 11 is connected to a load output 21 of the load relay 20 and to a digital input 61 of the digital circuit 60.

[0026] The reference potential terminal 13 is, for example, a ground terminal or has another predetermined voltage potential.

[0027] The load relay 20 has a load output 21, a second load terminal 22, and a load control terminal 23. The load relay 20 has a specified minimum load voltage and a specified minimum load current. Oxidation of the contact poles of the load relay 20 can only be prevented by maintaining the minimum load voltage and the minimum load current.

[0028] Detector 30 is connected to module input 11 and is designed to detect bouncing of load relay 20. To detect bouncing, detector 30 includes, for example, a counter that counts and monitors signal edge changes of a signal applied to module input 11. If, for example, a signal undergoes multiple edge changes within a predetermined time, for example, more than two edge changes within 10 ms, the edge change is classified as bouncing.

[0029] The detector 30 is preferably connected to the switch control input 43 of the controllable switch 40 via a control line 31. Of course, it is also possible to alternatively select a controllable switch that is connected to the detector 30, for example, via a wireless communication interface.

[0030] The detector 30 is preferably connected to the reference potential terminal 13 (see dashed line in Fig. 1).

[0031] The detector 30 preferably includes a computing unit 32 and a memory 33. The method of using the load relay 20 with the digital circuit 60 will be discussed in detail later.

[0032] According to one embodiment, detector 30 is suitable for detecting a load current LI flowing through load 50. For this purpose, detector 30 comprises, for example, a Hall sensor. Detector 30 is also suitable for performing a voltage measurement across load 50.

[0033] The controllable switch 40 has a switch input 41, a switch output 42, and a switch control input 43. The switch input 41 is connected to the module input 11, and the switch 40 is adapted to be controlled via the switch control input 43 depending on a bounce of a load relay 20 detected by the detector 30. The switch 40 is, for example, a transistor.

[0034] The load 50 is electrically arranged between the switch output 42 and the reference potential terminal 13. The load 50 is thus connected to the switch output 42 via a first contact and to the reference potential terminal 13 via a second contact. The load 50 preferably has an adjustable resistance. The load 50 is connected, for example, to the detector 30. The resistance of the load 50 is preferably controllable or adjustable by the detector 30. The load 50 is configured, for example, as a resistor.

[0035] The digital circuit 60 has a digital input 61 connected to the module output 12. The digital circuit 60 is, for example, a sensor unit or another digital circuit. The digital circuit 60 cannot tolerate high voltages or high currents. The maximum permissible digital voltage of the digital circuit 60 is below the minimum permissible load voltage of the load relay 20. The maximum permissible digital current of the digital circuit 60 is below the minimum permissible load current of the load relay 20. The voltage and current consumption of the digital circuit 60 is limited, for example, to 30 V and 30 mA. The digital circuit 60 is preferably also connected to the reference potential terminal 13.

[0036] The voltage source 70 is connected to the load output 22 of the load relay 20. The voltage source 70 is suitable for providing a voltage of at least the minimum load voltage and a current of at least the minimum load current of the load relay 20. Instead of a voltage source, a current source can of course also be used. The current source 70 is preferably also connected to the reference potential terminal 13.

[0037] Relay controller 80 is connected to load control terminal 23 of load relay 20. Relay controller 80 is, for example, a transmitter of a field device. Relay controller 80 switches load relay 20, for example, depending on certain events or measured values ​​from the sensor unit.

[0038] The switching method according to the invention for using an electrical circuit 100 is discussed below.

[0039] First, the electrical circuit 100 described above is provided.

[0040] Next, a bounce of load relay 20 is detected by detector 30. During detection, the detector analyzes, for example, a signal at module input 11. The signal is, for example, a voltage signal. The voltage signal is generated by voltage source 70. Preferably, the edges of the signal are analyzed or evaluated. For example, detector 30 counts edge jumps of the signal. The detector has, for example, a microcontroller circuit. Detector 30 evaluates the signal, for example, only if several edge changes, e.g., at least two, have occurred within a defined time period (e.g., 10 ms).

[0041] Switch 40 is then switched depending on the detected bounce. This means that if bounce is detected, switch 40 is closed. This connects load 50. Thus, a predetermined load current LI flows through load 50. This load current LI does not flow into digital circuit 60, but only through load relay 20 to reference potential terminal 13. This ensures that digital circuit 60 is not subjected to a current greater than the maximum permissible digital current for digital circuit 60. At the same time, however, the minimum permissible load current of load relay 20 is reached.

[0042] According to an embodiment compatible and complementary with the embodiment described above, the computing unit 32 detects and stores a first closing time RC1 of the load relay 20, as well as a first opening time RO1 of the load relay 20 (see solid lines in Fig. 2). Based on the first closing time RC1 and the first opening time RO1, the detector 30 then controls the switch 40.

[0043] As in Fig. 2, the switch 40 is preferably controlled such that the switch 40 is closed after a predetermined waiting time TW, i.e., at the first closing time of the switch SC1. The first closing time of the switch SC1 is preferably a first closing time T1 before the first opening time RO1 of the load relay 20. The switch 40 preferably opens only after the first opening time RO1 of the load relay 20, namely at a first opening time of the switch SO1.

[0044] According to an embodiment of the invention, while the switch 40 is closed, i.e., the load current LI is flowing, this load current LI is determined by the detector 30. The detector 30 then adjusts the resistance value of the adjustable load 50 such that the load current LI and the measured voltage correspond to a predetermined minimum load power. This has the advantage that even if the voltage applied to the load relay 20 varies, a sufficient power is still drawn through the load relay 20. The aim here is that the load relay 20 is thus always applied with a constant power, e.g., 5V / 100mA and 20V / 20mA, in order to ensure a sufficient cleaning power for the contacts of the load relay 20.

[0045] According to one embodiment, the detector 30 "learns" from each switching cycle in order to optimize the subsequent switching cycles. This is, of course, only relevant for periodic and constant switching operations. This means that, for example, the total duration T0 during which the load relay 20 is closed is recorded and stored by the detector 30. Subsequently, in the next switching cycle, i.e. between a second closing time of the load relay RC2 and a second opening time of the load relay RO2 (see Fig. 2), a second closing time of switch SC2 is selected so that it occurs immediately before the second opening time of load relay RO2. In other words, the first closing time T1 is shortened, resulting in a shorter second closing time T2 (see Fig.2). This ensures that, on average, less energy flows through the load 50 to clean the contacts of the load relay 20 by means of the spark generated by the load current LI.

[0046] According to an alternative embodiment, the computing unit 32 generates a clock signal. The clock signal is, for example, a pulse width signal with a predetermined clock frequency. The detector 30 controls the switch 40 depending on the clock signal. This has the advantage that, for example, with a duty rate of 50%, a 50% probability is achieved that the load relay 20 will be energized upon opening, i.e., at the first opening time RO1. Thanks to the duty rate of 50%, however, on average only half as much current flows through the load 50 as during a normal switching phase of the switch 40. This saves energy, and at the same time, the load relay 20 is cleaned at regular intervals by the spark generated when the relay contacts open. This embodiment is, of course, compatible with all described embodiments.

[0047] Thanks to the electrical circuit 100 according to the invention and the method according to the invention, it is thus achieved that, for example, a PLC circuit is used to control the load relay 20 and to provide the voltage source 70, and at the same time, a digital circuit 60 is used at the module output 12. At the same time, the minimum voltages / currents of the load relay 20 and the maximum voltages / currents of the digital circuit 60 are taken into account. List of reference symbols 10 Compatibility module 11 Module input 12 Module output 13 Reference potential connection 20 load relays 21 Load output 22 Load input 23 Load control connection 30 detector 31 Control line 32 computing unit 33 storage 40 switches 41 Switch input 42 Switch output 43 Switch control input 50 load 60 digital circuit 61 Digital input 70 Voltage source 80 Relay control 100 electrical circuits RC1 first closing time of the load relay RO1 first opening time of the load relay SC1 first closing time of the switch SO1 first opening time of the switch RC2 second closing time of the load relay RO2 second opening time of the load relay SC2 second closing time of the switch SO2 second opening time of the switch LI load current T0 total duration TW waiting time T1 first closing time T2 second closing duration

Claims

[1] Compatibility module (10) for an electrical circuit (100), comprising: - a module input (11) which is suitable for being connected to a load output (21) of a load relay (20), - a module output (12) connected to the module input (11), - a reference potential connection (13), - a detector (30) connected to the module input (11) and suitable for detecting a bounce of a load relay (20), - a controllable switch (40) having a switch input (41), a switch output (42) and a switch control input (43), wherein the switch input (41) is connected to the module input (11) and the switch (40) is suitable for being controlled by the detector (30) via the switch control input (43) depending on a detected bounce of a load relay (20), - a load (50) electrically arranged between the switch output (42) and the reference potential terminal (13). [2] Compatibility module (10) according to one of the preceding claims, wherein the detector (30) comprises a computing unit (32) and a memory (33), wherein the computing unit (32) is suitable for detecting and storing a first closing time (RC1) of a load relay (20), as well as detecting and storing a first opening time (RO1) of the load relay (20), and controlling the switch (40) based on the first closing time (RC1) and the first opening time (RO1). [3] Compatibility module (10) according to one of the preceding claims, wherein the detector (30) comprises a computing unit (32), and the computing unit (32) is adapted to generate a clock signal (TS) and the detector (30) is adapted to control the switch (40) depending on the clock signal (TS). [4] Compatibility module (10) according to one of the preceding claims, wherein the load (50) has an adjustable resistance and the detector (30) is adapted to detect a load current (LI) flowing through the load (50), wherein the detector (30) is connected to the load (50) in such a way as to adjust the adjustable resistance of the load (50) depending on the load current (LI) flowing through the load (50). [5] Electrical circuit (100) for a field device, comprising: - a compatibility module (10) according to one of the preceding claims, - a load relay (20) with a load output (21), a load input (22) and a load control connection (23), - a digital circuit (60) having a digital input (61), the digital input (61) being connected to the module output (12), - a voltage source (70) connected to the load input (22) of the load relay (20), a relay control (80) connected to the load control terminal (23). [6] A method of using an electrical circuit (100) comprising: - Providing an electrical circuit (100) according to claim 5, - detecting a bounce of the load relay (20) by the detector (30), - Switching the switch (40) depending on the bounce detected by the detector (30). [7] Method according to claim 6, wherein the detector (30) comprises a computing unit (32) and a memory (33), wherein the computing unit (32) detects and stores a first closing time (RC1) of the load relay (20) and detects and stores a first opening time (RO1) of the load relay (20), and controls the switch (40) based on the first closing time (RC1) and the first opening time (RO1). [8] Method according to claim 6 or 7, wherein the detector (30) comprises a computing unit (32), and the computing unit (32) generates a clock signal (TS) and the detector (30) controls the switch (40) depending on the clock signal (TS). [9] Method according to one of claims 6 to 8, wherein the load (50) comprises an adjustable resistance and the detector (30) determines a load current (LI) flowing through the load (50), wherein the detector (30) is connected to the load (50) and adjusts the resistance of the load (50) depending on the load current (LI) flowing through the load (50).

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