Transmitting device for transmitting digital signals between galvanically isolated circuit parts and field device having such a transmitting device

Abstract

The invention relates to a transmission device (100) comprising two galvanically isolated sub-circuits (110, 50). The first sub-circuit (110) comprises a carrier signal source (116) for outputting a carrier signal, a digital signal source (112) for outputting a binary signal level, and a logic component (118) for performing an AND operation on two input signals, the logic component having two logic inputs and a first logic output (130), the logic inputs being connected to the signal level output and the carrier signal source output, respectively. The second sub-circuit (150) comprises a signal input (154), a signal output (164), and a first RC element (160, 162), the signal input (154), the signal output (164), and the RC element (160, 162) being connected in parallel with respect to a second reference potential. A first isolation capacitor (202) is connected between the first logic output and the signal input for galvanic isolation. A second isolation capacitor (204) is connected between a first reference potential and the second reference potential for galvanic isolation.

Description

TECHNICAL FIELD

[0001] The application relates to a transmission device for transmitting digital signals between current-isolated circuit parts, and to a field device having such a transmission device. SUMMARY

[0002] It is an object of the application to provide a transmission device and a field device having such a transmission device which can simply transmit digital signals between different circuit parts of a modular electronic unit, in particular of a field device electronic unit. This object is achieved according to the application by a field device.

[0003] The transmission device according to the application comprises a first sub-circuit and a second sub-circuit which is current-isolated from the first sub-circuit and is further configured to supply power from the first sub-circuit and / or to communicate with the first sub-circuit via digital signals, which are transmitted as a time sequence of binary signal levels; wherein the first sub-circuit comprises a carrier signal source configured to output a carrier signal having a constant carrier frequency and a constant amplitude to a carrier signal output; a digital signal source configured to output a binary signal level having an available signal frequency at a signal level output, which is not greater than 10% of the carrier frequency, for example not greater than 1% of the carrier frequency; a first logic component configured to perform an AND operation on two input signals and having a first logic input, a second logic input and a first logic output configured to output a first logic output signal relative to a first reference potential, wherein the first logic input is connected to the signal level output, wherein the second logic input is connected to the carrier signal source output; wherein the second sub-circuit comprises a signal input; a signal output; a first RC element; wherein the signal input, the signal output and the RC element are connected to each other in parallel with respect to a second reference potential; wherein a first isolation capacitor is connected between the first logic output and the signal input for current isolation; and wherein a second isolation capacitor is connected between the first reference potential and the second reference potential for current isolation.

[0004] In a development of the application, the first isolation capacitor and the second isolation capacitor each comprise a series circuit of a plurality of capacitors, in particular a series circuit of three capacitors.

[0005] In a development of the application, the signal input comprises at least two Schottky diodes arranged in parallel with the first RC element and in series with each other, wherein the first isolation capacitor is connected to the signal input between the at least two Schottky diodes.

[0006] In a development of the application, the carrier signal source comprises an oscillator.

[0007] In a development of the application, the first Schmitt trigger is arranged between the first logic output and the first isolation capacitor.

[0008] In a development of the application, the second Schmitt trigger is arranged between the first RC element and the signal output.

[0009] In a development of the application, the carrier signal frequency is not less than 1 MHz, in particular not less than 2 MHz, wherein the usable signal frequency is not less than 10 kHz, for example not less than 20 kHz, in particular not less than 40 kHz.

[0010] In a development of the application, the transmission device comprises a CPLD (complex programmable logical device) or a microcontroller, wherein the carrier signal source and the first logic component are integrated into the CPLD or the microcontroller.

[0011] In a development of the application, the signal output is connected to a bus, in particular an I 2 C bus.

[0012] In a development of the application, the transmission device further comprises a reverse transmission path for transmitting a digital signal from the second subcircuit to the first subcircuit, wherein the transmission path comprises a second logic component configured to perform an AND operation on two input signals and having a third logic input, a fourth logic input and a second logic output, wherein the third logic input is connected to the bus, wherein the fourth logic input is applied with the potential tapped between the first isolation capacitor and the first RC element, wherein the second logic output is connected to the signal input of the first circuit part via a third isolation capacitor.

[0013] In a development of the application, the transmission device comprises a second CPLD or a microcontroller, wherein the second logic component is integrated into the second CPLD or the microcontroller.

[0014] In a development of the application, the signal source comprises a microprocessor.

[0015] The field device in the industrial process measurement technology according to the application comprises a transmission device according to the application, wherein the first subcircuit comprises a main electronics unit of the field device, wherein the second subcircuit comprises a sensor electronics unit of the field device, wherein the sensor electronics unit comprises an I 2 C converter for converting a main signal depending on a measured value into a digital signal, which is to be output to the first subcircuit via an I 2 C bus and the reverse transmission path.

[0016] In a development of the application, the I 2The C converter comprises a capacitive converter. BRIEF DESCRIPTION OF DRAWINGS

[0017] The application is described below on the basis of exemplary embodiments shown in the drawings. In the drawings:

[0018] Figure 1 a schematic diagram of a first exemplary embodiment of a transmission device according to the application is shown;

[0019] Figure 2 a signal diagram during operation of the transmission device Figure 1

[0020] Figure 3 an exemplary embodiment of an energy transmission circuit for a transmission device according to the application is shown; and

[0021] Figure 4 an exemplary embodiment of a field device according to the application is shown. DETAILED DESCRIPTION

[0022] Figure 1 The exemplary embodiment of the transmission device 100 shown comprises a first circuit portion 110 and a second circuit portion 150, wherein these two circuit portions are galvanically isolated from one another.

[0023] The first sub-circuit 110 comprises a digital signal source 112, in this case a microprocessor, which is configured to output a binary signal level with a usable signal frequency at a signal level output. The usable signal frequency may, for example, be 40 kHz. Furthermore, the first circuit portion 100 comprises a carrier signal source, in this case a clock signal generator 116, which has a frequency of, for example, 4 MHz. In this case, the clock signal frequency is one hundred times the usable signal frequency, which is more than sufficient. It is advantageous in any case, however, for the clock frequency to be at least ten times the usable signal frequency. The first sub-circuit further comprises a first logic component 118 for implementing an "and" operation between the two signals, which may, in its simplest form, be a discrete "and" gate. It is preferred in this case, however, for the first logic component 118 to be integrated into a CPLD or microcontroller together with the clock signal generator 116. The signal level output of the digital signal source 112 is connected to a first logic input 114 of the first logic component 118, wherein a second logic input is connected to the output of the clock generator 116.

[0024] Figure 2 ​The sequence of binary signal levels at the first logic input 114, by way of example 1 and 0, is shown by the curve 114. The resulting signal at the first logic output 130 of the first logic component 118 is represented by the curve 130. If the level at the first logic input 114 assumes the higher value 1, a carrier signal will be output at the first logic output 130; otherwise the opposite applies. This 4 MHz oscillation signal can be transmitted to the galvanically isolated second subcircuit 150 via the first isolation capacitor 202.

[0025] In the figure, the first isolation capacitor 202 is represented as a single capacitor Cl. In reality, the first isolation capacitor 202 is implemented as a series circuit of three capacitors for reasons related to explosion protection. The same applies to the second isolation capacitor 204, which is arranged between the reference potential of the first subcircuit 110 and the second subcircuit 150.

[0026] The second subcircuit 150 comprises a signal input 154 connected to the first isolation capacitor 202, a signal output 164 and a first RC element with a first smoothing capacitor 160 and a first discharge resistor element 162. The signal input 154, the signal output 164, the first smoothing capacitor 160 and the discharge resistor element 162 are connected to one another in parallel with respect to a second reference potential. A first Schottky diode 156 is arranged between the signal input 154 and the RC element or the signal output, wherein a second Schottky diode 158 is connected between the second reference potential and the signal input 154. The first smoothing capacitor can have a capacitance of, for example, several 10 pF, in particular 40 pF to 60 pF. The discharge resistor element can have a resistance value of, for example, several kΩ, in particular 20 kΩ to 30 kΩ. In Figure 2 In, the resulting smoothed signal at the signal output 164 is represented as the curve 164. It can be seen that the signal fed in at the first logic input 114 of the digital signal source 112 is reliably transmitted and without delay, with a signal swing that is suitable for further processing.

[0027] Figure 3 An exemplary embodiment of a transmission device 300 for supplying electrical power from a first circuit part 310 to a second circuit part 350 is shown, wherein the two circuit parts are galvanically isolated from one another. The transmission principle is identical to that described in Figure 1The similarity is that in this case, neither a digital signal source nor a logic component is required to implement the AND operation. Also, the discharge resistor element is eliminated. The first subcircuit 310 comprises a carrier signal source, in this case a switch controller 316, for example a TPS 62240 with a frequency of, for example, 1 MHz to 2 MHz. This high-frequency signal can be transmitted to the galvanically isolated second subcircuit 350 via a first isolation capacitor 302. In the figure, the first isolation capacitor 302 is represented as a single capacitor Cl. In reality, the first isolation capacitor 302 is implemented as a series circuit of three capacitors for reasons related to explosion protection. The same applies to the second isolation capacitor 304, which is arranged between the reference potentials of the first subcircuit 310 and the second subcircuit 350. The second subcircuit 350 comprises a power signal input 354, a power signal output 364 and a smoothing capacitor 360, which are connected to the first isolation capacitor 302. The power signal input 354, the power signal output 364 and the smoothing capacitor 360 are parallel to one another with respect to the second reference potential. A first Schottky diode 356 is arranged between the power signal input 354 and the smoothing capacitor 360 or the power signal output 364, wherein a second Schottky diode 358 is connected between the second reference potential and the power signal input 354. The first smoothing capacitor can have a capacitance of, for example, several μF, in particular 10 μF to 100 μF. Figure 3 The transmission device shown can be combined well with the first exemplary embodiment in order to implement a power supply to the second subcircuit.

[0028] The application can be implemented in particular in field devices of industrial process measurement technology, wherein such field devices are configured to detect a measured value, such as a fill level, a flow pressure temperature, a pH value, a density viscosity, an electrical conductivity or a substance concentration, and to output a corresponding measurement signal.

[0029] Figure 4 An exemplary embodiment of an operating circuit of a field device 10 is initially illustrated based on the first exemplary embodiment of the transmission device. The field device 10 comprises a first subcircuit 110 and a second subcircuit 150, which is galvanically isolated from the first subcircuit 110 by means of isolation capacitors 202, 204, 402. With regard to the components provided with the same reference numerals, the corresponding applies with regard to the Figure 1 Figure 1 ​The first sub-circuit 110 further includes the function of a main electronic unit that ensures communication with the control system and power supply of the field device 10 in a known manner. Although the circuit components upstream of the first logic output 130 are not shown, they are of course present. As a supplement to the first exemplary embodiment, a first Schmitt trigger 127 for regulating the signal to be transmitted is arranged between the first logic output and the first isolation capacitor 202. A second Schmitt trigger 167 is arranged between the RC element and the signal output 167. This eliminates... Figure 2 The time spread edge of signal 164 is shown. A so-called pull-up resistor element 165 is arranged immediately before signal output 164 and has a resistance value of, for example, 10kΩ. Signal output 164 is connected via I... 2 The C-bus is connected to the communication interface of the measurement converter 180, which generates a digital signal dependent on the analog master signal of the analog measurement circuit 190. This circuit further includes a return signal path for transmitting the digital signal to the first circuit section or main electronic unit. The digital signal is output to signal output 164. From there, the digital signal branches to the third logic input of the second logic component 418, which in turn performs an AND operation on the input signal. If a signal is to be transmitted from the measurement converter, the output of the digital signal source 112 is set to "high". Therefore, the carrier signal is continuously transmitted and reaches the fourth logic input of the second logic component 418.

[0030] To output "high", the measurement converter 180 is connected to a high input impedance that is substantially higher than the resistance of the pull-up resistor element 165. Therefore, the continuous "high" level set by the Schmitt trigger 167 is routed to the third logic input of the second logic component.

[0031] To output "low", the measurement converter 180 is connected to a low input impedance that is substantially lower than the resistance of the pull-up resistor element 165. Therefore, the continuous "high" level set by the Schmitt trigger 167 collapses after the pull-up resistor element 165, which produces the desired "low" at the third logic input.

[0032] The second logic output of the second logic component 418 outputs the output signal to the return signal input 454 of the first sub-circuit 110 via the third isolation capacitor 402. There are two Schottky diodes 456 and 458 on both sides of the return signal input.

[0033] From the return signal input 454, the signal reaches a return signal output 464, wherein the return signal input 454 is connected in parallel with the return signal output at a second smoothing capacitor 460 and a second discharge resistance element 462 with respect to the first reference potential. The capacitance of the second smoothing capacitor 460 is substantially the same as the capacitance of the first smoothing capacitor 160. The resistance of the second discharge resistance element 462 is substantially the same as the resistance of the first discharge resistance element 162.

[0034] Capacitive measurement transducers, for example the measurement transducer designated FDC2212 from Texas Instruments, are used as measurement transducers, in particular.

Claims

1. A field device of industrial process measurement technology, comprising a transmitting device (100), the transmitting device comprising: a first sub-circuit (110); and a second sub-circuit (150) galvanically isolated from the first sub-circuit, the second sub-circuit (150) being configured to be supplied with electrical power from the first sub-circuit and / or to communicate with the first sub-circuit via a digital signal, the digital signal being transmitted as a time sequence of binary signal levels; wherein the first sub-circuit (110) comprises: a carrier signal source (116) configured to output a carrier signal having a constant carrier frequency and a constant amplitude at a carrier signal source output; a digital signal source (112) configured to output a binary signal level having an available signal frequency at a signal level output, the available signal frequency not being larger than 10% of the carrier frequency; a first logic component (118) configured to perform an AND operation on two input signals and having a first logic input, a second logic input and a first logic output (130) configured to output a first logic output signal relative to a first reference potential, wherein the first logic input is connected to the signal level output, wherein the second logic input is connected to the carrier signal source output; and a main electronics unit of the field device; wherein the second sub-circuit (150) comprises: a signal input (154); a signal output (164); a first RC element (160, 162); and a sensor electronics unit of the field device; wherein the signal input (154), the signal output (164) and the first RC element (160, 162) are connected to each other in parallel with respect to a second reference potential; wherein the signal output is connected to I 2 C bus; The field device further comprises a reverse transmission path for transmitting digital signals from the second sub-circuit to the first sub-circuit, wherein the reverse transmission path comprises a second logic component configured to perform an AND operation on two input signals and having a third logic input, a fourth logic input and a second logic output, wherein the third logic input is connected to the I 2 C bus, wherein the fourth logic input is applied with a potential tapped between a first isolation capacitor and the first RC element, wherein the second logic output is connected to a signal input of the first sub-circuit via a third isolation capacitor; The sensor electronic unit includes I 2 C converter, the I 2 The C-type converter is used to convert a master signal that depends on the measurement value into a digital signal, which will then be transmitted via the I-type converter. 2 The C bus and the reverse transmission path are output to the first sub-circuit; wherein a first isolation capacitor (202) is connected between the first logic output and the signal input for galvanic isolation; and wherein a second isolation capacitor (204) is connected between the first reference potential and the second reference potential for galvanic isolation. the available signal frequency is not larger than 1% of the carrier frequency.

2. The field device of claim 1, wherein, the first isolation capacitor and the second isolation capacitor each comprise a series circuit of a plurality of capacitors.

3. The field device of claim 1, wherein, the first isolation capacitor and the second isolation capacitor each comprise a series circuit of three capacitors.

4. The field device of claim 3, wherein, the signal input comprises at least two Schottky diodes arranged in parallel with the first RC element and in series with each other, wherein a first isolation capacitor between the at least two Schottky diodes is connected to the signal input.

5. The field device of claim 1, wherein, the carrier signal source comprises an oscillator.

6. The field device of any one of claims 1-5, wherein, a Schmitt trigger is arranged between the first logic output and the first isolation capacitor.

7. The field device of any one of claims 1-5, wherein, a Schmitt trigger is arranged between the first RC element and the signal output.

8. The field device of any one of claims 1-5, wherein, the carrier signal frequency is not smaller than 1 MHz, wherein the available signal frequency is not smaller than 10 kHz.

9. The field device of any one of claims 1-5, wherein, ​ 10. The field device of claim 9, wherein, The carrier signal frequency is not less than 2 MHz.

11. The field device of claim 9, wherein, The available signal frequency is not less than 20 kHz.

12. The field device of claim 11, wherein, The available signal frequency is not less than 40 kHz.

13. The field device of any one of claims 1-5, comprising a first CPLD or microcontroller, wherein, The carrier signal source and the first logic component are integrated into the first CPLD or the microcontroller.

14. The field device of claim 1, further comprising a second CPLD or microcontroller, wherein, The second logic component is integrated into the second CPLD or the microcontroller.

15. The field device of any one of claims 1-5, wherein, The digital signal source includes a microprocessor.

16. The field device of claim 1, wherein, The I 2 The C converter includes a capacitance converter.

Images