Circuit for analog-to-digital conversion

Abstract

A circuit for analog-to-digital conversion is shown, having a first terminal, a second terminal, a third terminal, and a fourth terminal; an analog-to-digital converter (ADC); a first current source circuit for outputting a first output current; a first switching device for switchable connection of the first current source circuit to either the first terminal or the third terminal; a pull-in / sink current circuit for outputting a second output current; a second switching device for switchable connection of the pull-in / sink current circuit to either a reference potential or the second terminal; and a third switching device for switchable connection of the reference potential to either the second terminal or the fourth terminal. The terminals are for connecting sensors. A first input terminal of the ADC is connected to the first terminal, and a second input terminal of the ADC is connected to the second terminal.

Description

Technical Field

[0001] This invention relates to a circuit for analog-to-digital conversion. More particularly, it relates to a current transformer having a circuit for analog-to-digital conversion. Background Technology

[0002] A current transformer can convert analog signals into digital values ​​and map those digital values ​​to measured values ​​(such as physical parameters) using a nonlinear measurement function. Summary of the Invention

[0003] The circuit for analog-to-digital conversion according to the present invention includes a first terminal, a second terminal, a third terminal, and a fourth terminal; an analog-to-digital converter (ADC); a first current source circuit for outputting a first output current; a first switching device for switchable connection of the first current source circuit to either the first terminal or the third terminal; a pull-in / sink current circuit for outputting a second output current; a second switching device for switchable connection of the pull-in / sink current circuit to either a reference potential or the second terminal; and a third switching device for switchable connection of the reference potential to either the second terminal or the fourth terminal. The terminals are used to connect sensors. The first input terminal of the ADC is connected to the first terminal, and the second input terminal of the ADC is connected to the second terminal.

[0004] Here, the concept of "circuit" as used in the specification and claims is particularly understood as an arrangement of electrical and electronic components connected in a functional manner. For example, the circuit may be a component of a current transformer that converts sensor signals into measured values. In addition to the circuit according to the invention, the current transformer may be provided with a circuit (e.g., a processor) designed to map digital values ​​output by an ADC to measured values ​​based on a nonlinear measurement function. Here, the concept of "processor" as used in the specification is particularly understood as an electronic circuit designed to execute commands from a set of commands (assigned to the processor), wherein the order of the commands (and, if necessary, the arguments assigned to the commands) can be predetermined by a program executed by the processor. Furthermore, the concept of "nonlinear measurement function" as used in the specification is particularly understood as a nonlinear assignment rule (e.g., a calculation rule) by which measured values ​​can be assigned to digital values. Measured values ​​may, for example, point to a quantitative description of a physical parameter, such as the temperature level at a particular location. Measured values ​​may, for example, be digital values ​​provided digitally by the processor.

[0005] A circuit (or a current transformer when the circuit is a component of a current transformer) can be housed in a device. This device can be configured as an input / output module (I / O module). Here, the concept of "I / O module" as used within the scope of this specification is specifically understood as a module that can be connected in series or has been connected in series to a front-end, connecting one or more field devices (e.g., sensors and / or actuators) to the front-end and, if necessary, to a higher-level control device (via the front-end). In this regard, the concept of "front-end" as used within the scope of this specification is understood as a component of a modular fieldbus node whose task is to make data and / or services of the I / O modules connected in series to the front-end available via the fieldbus connected to the front-end.

[0006] Furthermore, the concept of "input terminal" as used in the specification and claims should be understood in particular as an electrical terminal through which electrical signals (e.g., voltage and / or current values) can be read (and thus further processed in the ADC). Here, the concept of "terminal" as used in the specification and claims should be understood in particular as an electrical contact location (e.g., a terminal location having an electrical conductor, such as a tension spring terminal), designed to be temporarily or continuously connected to an electrical conductor. Furthermore, the concept of "analog-to-digital converter" as used in the specification and claims should be understood in particular as a circuit that determines which of a plurality of value ranges an analog value belongs to and outputs a digital value corresponding to the respective value range. The digital value can, for example, be output as a bit sequence.

[0007] Furthermore, the concept of "current source circuit" as used in the specification and claims is particularly understood as a circuit designed to output a current of a specific intensity. This specific intensity can be positive or negative. Furthermore, the concept of "switching device" as used in the specification and claims is particularly understood as an electronic switch or an arrangement of multiple electronic switches (e.g., a reversing switch). Furthermore, the concept of "pull-sink current circuit" as used in the specification and claims is particularly understood as a circuit designed to output or input a current of a specific intensity. In particular, this intensity can alternate between positive and negative values.

[0008] Furthermore, the ordinal numbers “first,” “second,” etc., used in the specification and claims do not specify an order, but are only used to list and distinguish features.

[0009] The ADC may have a third input terminal and a fourth input terminal, wherein the first current source circuit is connected to the first switching device via a resistor, and wherein the third input terminal and the fourth input terminal are connected to the resistor.

[0010] The first switching device may have a leakage current of less than 3mA, and preferably less than 30μA.

[0011] The circuit may have a control circuit for controlling the switching device, wherein the control circuit is designed to switch between multiple measurement modes.

[0012] In the first measurement mode, the first switching device can connect the first current source circuit to the first terminal ground, the second switching device can connect the pull-in current circuit to the reference potential ground, and the third switching device can connect the reference potential to the second terminal ground.

[0013] In the second measurement mode, the first switching device can connect the first current source circuit to the first terminal ground, the second switching device can connect the pull-sink current circuit to the second terminal ground, and the third switching device can connect the reference potential to the fourth terminal ground.

[0014] In the third measurement mode, the first switching device can connect the first current source circuit to the third terminal ground, the second switching device can connect the pull-in current circuit to the reference potential ground, and the third switching device can connect the reference potential to the fourth terminal ground.

[0015] In the fourth measurement mode, the first switching device can connect the first current source circuit to the first terminal ground, the second switching device can connect the pull-in current circuit to the reference potential ground, and the third switching device can connect the reference potential to the fourth terminal ground.

[0016] The ADC has a fifth input terminal and a sixth input terminal, wherein the fifth input terminal and the sixth input terminal are connected to the measuring resistor.

[0017] In the fifth measurement mode, the first switching device can connect the first current source circuit to the reference potential via the measuring resistor, the second switching device can connect the pull-in current circuit to the reference potential, and the third switching device can connect the reference potential to the fourth terminal. The analog-to-digital converter is designed to read the voltage drop across the measuring resistor via the fifth and sixth input terminals.

[0018] The circuit for analog-to-digital conversion may have a fourth switching device for a switchable connection between a constant voltage and a third terminal.

[0019] In the sixth measurement mode, the second switching device can connect the pull-in current circuit to the second terminal ground, the third switching device can connect the reference potential to the fourth terminal ground, and the fourth switching device can connect the constant voltage to the third terminal ground.

[0020] Furthermore, it goes without saying that the features described in conjunction with the circuit can also be features of the method of applying the circuit. Attached Figure Description

[0021] The invention will then be described in detail with reference to the embodiments, wherein, with reference to the accompanying drawings, in which:

[0022] Figure 1 A block diagram of a fieldbus system is shown, which includes multiple modular fieldbus nodes;

[0023] Figure 2 A block diagram of a modular fieldbus node is shown, the fieldbus node including a front end and multiple I / O modules, as well as fieldbus devices connected to the I / O modules;

[0024] Figure 3 A block diagram of an I / O module is shown, the I / O module being equipped with measurement electronics.

[0025] Figure 4 A block diagram of a circuit is shown, which is part of a measuring electronic component;

[0026] Figure 5 This illustrates the application of the circuit in implementing the first measurement mode;

[0027] Figure 6 This illustrates the application of the circuit in implementing the second measurement mode;

[0028] Figure 7 This illustrates the application of the circuit in implementing the third measurement mode;

[0029] Figure 8 This illustrates the application of the circuit in implementing the fourth measurement mode;

[0030] Figure 9 This illustrates the application of the circuit in implementing the fifth measurement mode; and

[0031] Figure 10 The circuit is shown for application in implementing the sixth measurement mode.

[0032] Here, the same or functionally similar elements are indicated by the same reference numerals in the figures. Detailed Implementation

[0033] Figure 1A block diagram of a fieldbus system is shown. The fieldbus system 10 includes a higher-level control unit 20 and modular fieldbus nodes 100, interconnected via a fieldbus 30 (signal-technically). The higher-level control unit 20 can be used not only to monitor but also to regulate devices (not shown) controlled by the fieldbus system 10. When the higher-level control unit 20 monitors devices, it can periodically or aperiodically receive status data from the fieldbus nodes 100, which describes the status of the devices and generates fault or alarm signals when the status of the devices deviates (substantially) from a desired / permissible status or a status range. When the higher-level control unit 20 (not only monitors but also regulates) devices, it can periodically or aperiodically receive status data from the fieldbus nodes 100 and determine the control data to be transmitted to the fieldbus nodes 100, taking the status data into account.

[0034] Figure 2 A block diagram of a modular fieldbus node is shown. Fieldbus node 100 includes a front-end 110 and two I / O modules 120 and 130 connected in series with the front-end 110. Sensors 140 and 150 are connected to I / O module 120, and sensors 160 and 170 are connected to I / O module 130. During operation, I / O modules 120 and 130 read sensor signals and generate status data from the sensor signals, transmitting the sensor signals to the front-end 110 via a local bus 180. The front-end 110 can process the status data locally and / or (in a modified form if necessary) continue to transmit the status data to a higher-level control unit 20. The higher-level control unit 20 (or the front-end 110 in the case of local processing) can generate control data taking the status data into account.

[0035] Control data generated by the upper-level control unit 20 can be transmitted via fieldbus 30 to (the same or another) front-end. Control data transmitted to the front-end (or generated by the front-end 110) can (if necessary, in an improved form) continue to be transmitted / transmitted to other I / O modules (if necessary, to other I / O modules of fieldbus node 100). The I / O module receiving the control data can output control signals conforming to the control data at the output terminal connected to the actuator. Here, data communication between components of the fieldbus system 10, mapping of sensor signals to status data, and mapping of control data to control signals can be adapted to different application scenarios through the configuration of one or more fieldbus nodes 100.

[0036] Figure 3A block diagram of I / O module 130 is shown. I / O module 130 includes interface 132 and interface 134. Both interface 132 and interface 134 include four terminals. Sensor 140 is connected to I / O module 130 via interface 132. Sensor 150 is connected to I / O module 130 via interface 134. Sensors 140 and 150 can be, for example, temperature sensors or thermistors such as resistance temperature sensors. Interfaces 132 and 134 are connected to (input) circuitry 200. Circuitry 200 can be designed to apply a defined voltage to sensors 140 and 150 or to generate a defined current through sensors 140 and 150.

[0037] Circuit 200 can also be designed to detect the current passing through sensors 140 and 150, or measure the voltage drop across sensors 140 and 150, or generate an analog voltage or current proportional to the current / voltage drop. I / O module 130 also includes an ADC 300 and a microcontroller 400. The analog-to-digital converter 300 is designed to convert analog voltage / current into digital values. The microcontroller 400 has a processor and immutable memory. A program executed by the processor is stored in the immutable memory, and this program assigns measurement values ​​to the sensor signals converted into digital values ​​by the ADC 300. Similar to... Figure 3 The dual-channel I / O module 130 shown can also be provided as a single-channel, three-channel, four-channel, or multi-channel I / O module.

[0038] Figure 4 A block diagram of circuit 200 and ADC 300 is shown. Circuit 200 includes terminals 201, 202, 203, and 204 for connecting sensor 140 or sensor 150. Figure 3 As shown, depending on the sensor type, terminals 203 and / or 204 may be occupied or unoccupied. Input terminals 301 and 302 of the ADC 300 are connected to terminal 201 or terminal 203. Circuit 200 includes a current source circuit 210 and a switching device 230 for switchable connection of the current source circuit 210 to terminal 201 or terminal 203. The switching device 230 may be formed by two electronic switches arranged in series, preferably having a leakage current of less than 3 mA, and particularly preferably less than 30 μA.

[0039] The current source circuit 210 is connected to the switching device 230 via resistor 280, wherein the ADC 300 can determine the voltage drop across resistor 280 via input terminals 303 and 304. This voltage drop can be used as a reference voltage for the test current output by the current source circuit 210. Circuit 200 also includes a measuring resistor 290 (e.g., a resistance thermometer), wherein the ADC 300 can determine the voltage drop across the measuring resistor 290 via input terminals 305 and 306.

[0040] Circuit 200 further includes a pull-in / sink current circuit 220 and a switching device 240 for switchable connection of the pull-in / sink current circuit 220 to a reference potential (e.g., ground) or terminal 202. Circuit 200 also includes a switching device 250 for switchable connection of the reference potential to terminal 202 or terminal 204. Furthermore, circuit 200 includes a switching device 260 for switchable connection of a constant voltage (e.g., 2.4V) to terminal 203. Switching devices 240, 250, and 260 preferably also have a leakage current of less than 3mA, and particularly preferably less than 30μA.

[0041] To control switching devices 230, 240, 250, and 260, circuit 200 includes control circuitry 270, which is designed to switch between multiple measurement modes. For each measurement mode, the switching position of the switching device can be stored in the memory of control circuitry 270. Signals for the switching can be received via local bus 180 or input via input devices on I / O module 130. Control circuitry 270 can also be designed to internally generate signals for the switching when it detects sensor 140 or sensor 150.

[0042] Figure 5 The circuit 200 is illustrated in its application to a first measurement mode in which sensor 140 or sensor 150 is configured, for example, as a two-wire resistance thermometer. In this measurement mode, switching device 230 connects current source circuit 210 to terminal 201, switching device 240 connects pull-in / sink current circuit 220 to a reference potential, and switching device 250 connects the reference potential to terminal 202. Therefore, a test current I1 flows through sensor 140 or sensor 150, and the voltage drop across sensor 140 or sensor 150 can be determined by the potential difference between input terminals 301 and 302. The temperature value can be derived from this voltage drop, for example.

[0043] Figure 6The circuit 200 is illustrated in its application to a second measurement mode, in which sensor 140 or sensor 150 is configured, for example, as a three-wire resistance thermometer. In this measurement mode, switching device 230 connects current source circuit 210 to terminal 201, switching device 240 connects pull-in / sink current circuit 220 to terminal 202, and switching device 250 connects a reference potential to terminal 204. Therefore, a test current I1 flows through sensor 140 or sensor 150, and the voltage drop across sensor 140 or sensor 150 can be determined by the potential difference between input terminals 301 and 302. The temperature value can be derived from this voltage drop, for example. To compensate for line resistance, pull-in / sink current circuit 220 can output a current exactly equal to the test current I1.

[0044] Figure 7 The circuit 200 is illustrated in its application to a third measurement mode, in which sensor 140 or sensor 150 is configured, for example, as a four-wire resistance thermometer. In this measurement mode, switching device 230 connects current source circuit 210 to terminal 203, switching device 240 connects pull-in / sink current circuit 220 to a reference potential, and switching device 250 connects the reference potential to terminal 204. Therefore, test current I1 flows through sensor 140 or sensor 150, and the voltage drop across sensor 140 or sensor 150 can be determined by the potential difference between input terminals 301 and 302. The temperature value can be derived from this voltage drop, for example. No line resistance compensation is required because there is no current flowing through terminals 201 and 202.

[0045] Figure 8 The circuit 200 is shown for implementation of a fourth measurement mode in which sensor 140 or sensor 150 is configured, for example, as a potentiometer. In this measurement mode, switching device 230 connects current source circuit 210 to terminal 201, switching device 240 connects pull-in / sink current circuit 220 to a reference potential, and switching device 250 connects the reference potential to terminal 204. Therefore, test current I1 flows through sensor 140 or sensor 150, and the voltage drop across sensor 140 or sensor 150 can be determined by the potential difference between input terminals 301 and 302. The position of a knob can be derived from this voltage drop, for example.

[0046] Figure 9The circuit 200 is illustrated for implementation of a fifth measurement mode in which sensor 140 or sensor 150 is configured, for example, as a thermistor. In this measurement mode, switching device 230 connects current source circuit 210 to a reference potential via measuring resistor 290, switching device 240 connects pull-in / sink current circuit 220 to the reference potential, and switching device 250 connects the reference potential to terminal 204. ADC 300 reads the voltage drop across measuring resistor 290 via inputs 305 and 306. Measuring resistor 290 may be a component of a resistance thermometer and is used to correct the thermistor voltage for temperature-related deviations.

[0047] Figure 10 The circuit 200 is illustrated for implementation of a sixth measurement mode, in which sensor 140 or sensor 150 is configured, for example, as a strain gauge. In this measurement mode, switching device 260 applies a constant voltage to terminal 203, switching device 240 connects pull-in current circuit 220 to terminal 202, and switching device 250 connects a reference potential to terminal 204. For example, the strain gauge can be configured as a bridge circuit, and the bridge center voltage can be determined by the potential difference between input terminals 301 and 302.

[0048] List of reference numerals

[0049] 10 Fieldbus System

[0050] 20 control units

[0051] 30 Fieldbus

[0052] 100 Fieldbus Nodes

[0053] 110 Front-end / Fieldbus Coupler

[0054] 120I / O module

[0055] 130I / O module

[0056] 132 interface

[0057] 134 interface

[0058] 140 sensors

[0059] 150 sensors

[0060] 160 sensors

[0061] 170 sensor

[0062] 180 local bus

[0063] 200 input circuit

[0064] 201 terminal

[0065] 202 terminal

[0066] 203 terminal

[0067] 204 terminal

[0068] 210 Current Source Circuit

[0069] 220 pull-in current sink circuit

[0070] 230 switching device

[0071] 240 switching device

[0072] 250 switching device

[0073] 260 switching device

[0074] 270 control circuit

[0075] 280 resistor

[0076] 290 Measuring Resistance

[0077] 300 analog-to-digital converter

[0078] 301 input terminal

[0079] 302 input terminal

[0080] 303 input terminal

[0081] 304 input terminal

[0082] 305 input terminal

[0083] 306 input terminal

[0084] 400 microcontroller.

Claims

1. A circuit used for analog-to-digital conversion. It has a first terminal (201), a second terminal (202), a third terminal (203), and a fourth terminal (204), which are used to connect sensors (140, 150). It has an analog-to-digital converter (ADC) (300), wherein a first input terminal (301) of the ADC is connected to a first terminal (201) and a second input terminal (302) of the ADC is connected to a second terminal (202). It has a first current source circuit (210) for outputting a first output current I1. It has a first switching device (230) for switchably connecting the first current source circuit (210) to either the first terminal (201) or the third terminal (203). It has a pull-in current sink circuit (220) for outputting the second output current I2. It has a second switching device (240) for switchably connecting the pull-in current circuit (220) to a reference potential or a second terminal (202), and It has a third switching device (250) for switching the reference potential to a second terminal (202) or a fourth terminal (204).

2. The circuit for analog-to-digital conversion according to claim 1, in, The ADC (300) has a third input terminal (303) and a fourth input terminal (304). The first current source circuit (210) is connected to the first switching device (230) via a resistor (280). The third input terminal (303) and the fourth input terminal (304) are connected to the resistor (280).

3. The circuit for analog-to-digital conversion according to claim 1, in, The first switching device (230) has a leakage current of less than 3mA.

4. The circuit for analog-to-digital conversion according to claim 1, in, The first switching device (230) has a leakage current of less than 30 μA.

5. The circuit for analog-to-digital conversion according to any one of claims 1 to 4, in, The circuit has a control circuit (270) for controlling the switching devices (230, 240, 250, 260), wherein the control circuit (270) is designed to switch between multiple measurement modes.

6. The circuit for analog-to-digital conversion according to claim 5, in, In the first measurement mode, the first switching device (230) electrically connects the first current source circuit (210) to the first terminal (201). In the first measurement mode, the second switching device (240) connects the pull-in current circuit (220) to the reference potential in a conductive manner, and In the first measurement mode, the third switching device (250) connects the reference potential to the second terminal (202) in a conductive manner.

7. The circuit for analog-to-digital conversion according to claim 5, in, In the second measurement mode, the first switching device (230) electrically connects the first current source circuit (210) to the first terminal (201). In the second measurement mode, the second switching device (240) electrically connects the pull-in current circuit (220) to the second terminal (202), and In the second measurement mode, the third switching device (250) connects the reference potential to the fourth terminal (204) in a conductive manner.

8. The circuit for analog-to-digital conversion according to claim 6, in, In the second measurement mode, the first switching device (230) electrically connects the first current source circuit (210) to the first terminal (201). In the second measurement mode, the second switching device (240) electrically connects the pull-in current circuit (220) to the second terminal (202), and In the second measurement mode, the third switching device (250) connects the reference potential to the fourth terminal (204) in a conductive manner.

9. The circuit for analog-to-digital conversion according to claim 5, in, In the third measurement mode, the first switching device (230) electrically connects the first current source circuit (210) to the third terminal (203). In the third measurement mode, the second switching device (240) connects the pull-in current circuit (220) to the reference potential in a conductive manner, and In the third measurement mode, the third switching device (250) connects the reference potential to the fourth terminal (204) in a conductive manner.

10. The circuit for analog-to-digital conversion according to any one of claims 6 to 8, in, In the third measurement mode, the first switching device (230) electrically connects the first current source circuit (210) to the third terminal (203). In the third measurement mode, the second switching device (240) connects the pull-in current circuit (220) to the reference potential in a conductive manner, and In the third measurement mode, the third switching device (250) connects the reference potential to the fourth terminal (204) in a conductive manner.

11. The circuit for analog-to-digital conversion according to claim 5, in, In the fourth measurement mode, the first switching device (230) electrically connects the first current source circuit (210) to the first terminal (201). In the fourth measurement mode, the second switching device (240) connects the pull-in current circuit (220) to the reference potential in a conductive manner, and In the fourth measurement mode, the third switching device (250) connects the reference potential to the fourth terminal (204) in a conductive manner.

12. The circuit for analog-to-digital conversion according to any one of claims 6 to 9, in, In the fourth measurement mode, the first switching device (230) electrically connects the first current source circuit (210) to the first terminal (201). In the fourth measurement mode, the second switching device (240) connects the pull-in current circuit (220) to the reference potential in a conductive manner, and In the fourth measurement mode, the third switching device (250) connects the reference potential to the fourth terminal (204) in a conductive manner.

13. The circuit for analog-to-digital conversion according to claim 5, in, The ADC (300) has a fifth input terminal (305) and a sixth input terminal (306), and The fifth input terminal (305) and the sixth input terminal (306) are connected to the measuring resistor (290).

14. The circuit for analog-to-digital conversion according to any one of claims 6 to 9, 11, in, The ADC (300) has a fifth input terminal (305) and a sixth input terminal (306), and The fifth input terminal (305) and the sixth input terminal (306) are connected to the measuring resistor (290).

15. The circuit for analog-to-digital conversion according to claim 13, in, In the fifth measurement mode, the first switching device (230) connects the first current source circuit (210) to the reference potential via the measuring resistor (290). In the fifth measurement mode, the second switching device (240) connects the pull-in current circuit (220) to the reference potential in a conductive manner. In the fifth measurement mode, the third switching device (250) connects the reference potential to the fourth terminal (204) in a conductive manner, and The analog-to-digital converter (300) is designed to read the voltage drop across the measuring resistor (290) via a fifth input terminal (305) and a sixth input terminal (306).

16. The circuit for analog-to-digital conversion according to claim 14, in, In the fifth measurement mode, the first switching device (230) connects the first current source circuit (210) to the reference potential via the measuring resistor (290). In the fifth measurement mode, the second switching device (240) connects the pull-in current circuit (220) to the reference potential in a conductive manner. In the fifth measurement mode, the third switching device (250) connects the reference potential to the fourth terminal (204) in a conductive manner, and The analog-to-digital converter (300) is designed to read the voltage drop across the measuring resistor (290) via a fifth input terminal (305) and a sixth input terminal (306).

17. The circuit for analog-to-digital conversion according to any one of claims 6 to 9, 11, 13, 15 to 16, It has a fourth switching device (260) for switching a constant voltage to the third terminal (203).

18. The circuit for analog-to-digital conversion according to claim 17, in, In the sixth measurement mode, the second switching device (240) electrically connects the pull-in current circuit (220) to the second terminal (202). In the sixth measurement mode, the third switching device (250) connects the reference potential to the fourth terminal (204) in a conductive manner. In the sixth measurement mode, the fourth switching device (260) connects a constant voltage to the third terminal (203) in a conductive manner.

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