DE102019103798A1 - Current source device for arrangement in a current loop - Google Patents

Abstract

Shown is a current source device (1) for a current loop (4) with a current regulator (5) with a series transistor (7), a transverse transistor (11) and a current output (13) with an output impedance (Z), the current regulator (5) a target current value (i) can be specified, the series transistor (7) serves as a current source for impressing a loop current (i), the current regulator (5) has a current control circuit and is set up to regulate to the target current value (i), the series transistor (7) lies in the current control loop and this has a first ring gain, the transverse transistor (11) in the current source device (1) serves as a current sink to divert part of the loop current (i) and the series transistor (7) has a first and the transverse transistor (11) a second transistor output impedance and the first and the second transistor output impedance form the output impedance (Z). The object of the invention is to provide a current source device (1) with enlarged r output impedance of the series transistor (7). This is achieved in that the current source device (1) has a voltage regulator (6), a target voltage value (u) can be given to it and it has the cross transistor (11), it has a voltage control loop and is set up is to regulate a series voltage (u) via the series transistor (7) to the nominal voltage value (u) by diverting part of the loop current (i), the cross transistor (11) is in the voltage control loop and the voltage control loop has a second ring gain, in the current control loop Amplifier (8) is arranged with a gain (v) to enlarge the first ring gain.

Description

The invention relates to a current source device for arrangement in a current loop with a current regulator, a transverse transistor and a current output with an output impedance. A nominal current value can be specified for the current regulator and the current regulator has a series transistor. The series transistor is arranged in the current source device as a current source for impressing a loop current into the current loop. The current regulator has a current control loop and is set up to regulate the loop current to the setpoint current value. The series transistor is in the current control loop and the current control loop has a first ring gain. The transverse transistor is arranged in the current source device as a current sink for diverting a predeterminable part of the loop current. The series transistor has a first transistor output impedance and the transverse transistor has a second transistor output impedance. The first transistor output impedance and the second transistor output impedance form the output impedance.

Current loops are used to supply electrical devices with electrical energy and to transmit information through electrical signals. A current loop usually has only two electrical conductors, via which electrical devices are supplied and information is transmitted. An electrical source, usually a voltage source, provides the electrical energy to supply the electrical devices. The electrical devices are connected to a current loop via a current interface. A power interface is used on the one hand to supply the device and on the other hand to transfer information by sending and / or receiving signals.

The electrical devices with a power interface are field devices, for example. These are used in particular in process automation. For example, they have actuators and sensors. Process automation deals with the automation of industrial processes, such as manufacturing processes. Industrial processes are influenced by actuators and monitored by sensors. Actuators are, for example, final control elements and valves and sensors are, for example, flow, level, temperature, pressure, analysis, gas or steam measuring devices. Flowmeters are, for example, magnetic-inductive flowmeters for measuring the flow of a medium through a measuring tube. Industrial processes are controlled by control and / or guidance systems using actuators and sensors. Process automation is only meaningfully possible when actuators and sensors can be centrally controlled by control and / or guidance systems.

The transmission of information, for example to control actuators and sensors, via a current loop can take place with analog and / or digital signals. In the case of an analog signal, information is encoded in a value of a loop current, for example. A loop current is an electrical current that flows through the electrical conductors of a current loop. The coding can be done, for example, according to the 20 mA standard. In this case, information is reproduced, for example, in the form of measured values using the value of a loop current that is in the range from 4 mA to 20 mA. The standard is in DIN IEC 60381-1 described. In the case of a digital signal, information is encoded in a frequency of a loop stream, for example. Digital signals can, for example, correspond to a HART standard. According to the HART standard, the digital value 1 corresponds to a frequency of 1.2 kHz and the digital value 0 corresponds to a frequency of 2.2 kHz. The implementation of both the 20 mA standard and the HART standard enables the simultaneous transmission of analog and digital signals.

A controller regulates a controlled variable to a specified setpoint value. The current regulator is a regulator in which the target current value is the target variable value, and the voltage regulator is a regulator in which the target voltage value is the target variable value. To regulate a controlled variable to a setpoint variable value, a controller has a control loop. In the control loop, a control deviation is first determined, which quantifies the deviation of the controlled variable from the setpoint value. A control device in the control loop determines a manipulated variable from the control deviation, which counteracts the control deviation. The manipulated variable becomes the controlled variable in the control loop via the controlled system, which is also arranged in the control loop. The ring gain is the gain a signal experiences as it passes through the control loop. The ring gain is thus determined by the control device and the controlled system.

The series transistor is arranged in the current source device as a current source for impressing the loop current in the current loop and is also located in the current control loop. A transistor like the series transistor basically has three electrical connections. The loop current thus flows into a first connection and out of a second connection. A third connection is used to control the transistor, so that only a current with the value of the nominal current value flows through the transistor. The series transistor has the first transistor output impedance. The first Transistor output impedance is the impedance on its second terminal.

The transverse transistor is arranged in the current source device as a current sink for diverting a predeterminable part of the loop current. The diverted portion of the loop current flows in and out of its second port. The third connection is used to control the transistor. The transverse transistor has the second transistor output impedance. The second transistor output impedance is the impedance at its second terminal.

The second connections of the series transistor and the transverse transistor are connected to the same node of the current source device, so that the output impedance is formed by the first and the second transistor output impedance and is applied to the current output. An increase in the amount of the output impedance is advantageous, since with such an increase the influence of the current source on signals transmitted via the current loop is reduced.

The object of the present invention is therefore to specify a current source device in which the magnitude of the output impedance is increased compared to the prior art described. The prior art described is known from practice.

The object is achieved by a power source device having the features of patent claim 1. According to the invention, the current source device has a voltage regulator, to which a setpoint voltage value can be specified and which has the transverse transistor. The voltage regulator has a voltage regulating circuit and is set up to regulate a series voltage via the series transistor to the target voltage value by diverting part of the loop current. The transverse transistor is in the voltage control loop and the voltage control loop has a second ring gain. An amplifier with a gain for increasing the first ring gain is arranged in the current control loop.

By arranging the amplifier in the current control loop, at least the first ring gain of the current control loop is increased, as a result of which the magnitude of the first transistor output impedance is increased at the same nominal voltage value across the series transistor. This also increases the magnitude of the output impedance. By increasing the magnitude of the output impedance, signals which are transmitted via the current loop are influenced by the current source device to a lesser extent than is known from the prior art.

In the prior art, a voltage across the series transistor is permanently set such that the first transistor output impedance is sufficiently high in all operating states. The first transistor output impedance is sufficiently high when the transmission of signals via the current loop is influenced by the output impedance, but not impaired. This is particularly relevant when signals are transmitted according to the HART standard.

The loop current multiplied by the series voltage drop across the series transistor is the power loss, which is converted into heat in the transistor. Electrical energy converted into heat is no longer available for implementing functionalities in devices. This is a problem in particular in current loops, as these only allow the transmission of low electrical power. This is particularly the case when explosion protection regulations are implemented that, for example, require devices to be intrinsically safe. Intrinsic security is achieved by limiting energy.

In devices known from the prior art, the series voltage drop across the series transistor cannot be further reduced in order to reduce the power loss without also impairing the transmission of signals via the current loop. This is especially true when transmitting HART signals. This is because a reduction in the longitudinal voltage is accompanied by a reduction in the amount of the first transistor output impedance and therefore also with a reduction in the output impedance. In contrast to this, in the case of the present power source device, the amplifier enables the longitudinal voltage to be reduced without adverse effects occurring. This also reduces the power loss.

In one embodiment of the current source device according to the invention, it is provided that the nominal voltage value is specified in such a way that the series transistor is in normal operation. While normal operation is a fixed term for bipolar transistors, this also refers to the saturation range for field effect transistors.

In a further embodiment it is provided that the first ring gain and the second ring gain are set such that the output impedance has a predetermined output impedance value.

In a further embodiment it is provided that the output impedance value satisfies a HART specification.

In a further embodiment it is provided that the first ring gain is set by the gain of the amplifier.

The series transistor and the amplifier are arranged in the current control loop. In one embodiment of the current source device, the amplifier is arranged in the current regulator for preferably direct control of the series transistor. Accordingly, the amplifier provides the signals with which the series transistor is preferably controlled directly at its third connection.

The series transistor is preferably a bipolar transistor. Field-effect transistors can also be used, but bipolar transistors in the present case have a higher output impedance than field-effect transistors and are also less sensitive to electrical interference signals. If the series transistor is a bipolar transistor, then it is also advisable to select the nominal voltage value in such a way that the bipolar transistor does not work in saturation mode, but still in normal operation.

The first ring gain of the current control loop has a ring bandwidth and the second ring gain of the voltage control loop also has a ring bandwidth. A bandwidth, such as the present ring bandwidths, indicates the frequency at which a ring gain is reduced to the absolute value 1 has fallen off. If HART signals are to be transmitted via the current loop, it is advisable to set up the current control loop and the voltage control loop in such a way that the ring bandwidth of the first ring gain and the ring bandwidth of the second ring gain include frequencies of HART signals. The ring bandwidths must therefore be greater than 2.2 kHz.

A ring bandwidth is determined by the components that are in the control loop. Since the amplifier is in the current control loop, it is advisable to set up the amplifier in such a way that an amplifier bandwidth of the amplifier includes the frequencies of HART signals. If, for example, the first ring bandwidth of the first ring amplification without the amplifier does not include frequencies of HART signals, then the first ring bandwidth can be increased by appropriately setting up the amplifier so that it includes frequencies of HART signals.

The current control loop, like every control loop, has feedback. In a further embodiment of the current source device it is provided that the feedback in the current control loop is set up for the gain of the amplifier in such a way that the ring bandwidth includes the frequencies of HART signals. The feedback is preferably frequency-dependent. Due to the frequency dependency of the feedback, the ring bandwidth can be adjusted so that it includes the frequencies of HART signals.

In detail, there is a multitude of possibilities for designing and developing the current source device. For this purpose, reference is made both to the claims subordinate to claim 1 and to the following description of a preferred exemplary embodiment of a power source in connection with the figure.

The figure shows essential features of an exemplary embodiment of a current source device 1 in an abstract representation. The power source device 1 is with a supply voltage source 2 and with a field device 3 via a current loop 4th connected. Through the design of the power source device 1 , this with the voltage source 2 and the field device 3 to connect, it is designed to be arranged in a current loop. She has a current regulator 5 and a voltage regulator 6th on.

The current regulator 5 has a series transistor 7th as a power source, an amplifier 8th , a first control device 9 and a shunt resistor 10 on. The series transistor 7th is designed as a pnp transistor and is in the current source 1 for impressing a loop current i _O in the current loop 4th arranged. The arrangement for impressing the loop current i _O in the current loop 4th is implemented in that the loop current i _O in the emitter (first connection) of the series transistor 7th in and out of the collector (second connection) of the series transistor 7th flows out. The amplifier 8th is in the current regulator 5 for direct control of the series transistor 7th arranged. This arrangement is achieved in that the output of the amplifier 8th with the base (third connection) of the series transistor 7th is directly connected. The amplifier 8th in turn is controlled by the first control device 9 controlled. The first control device 9 and thus the current regulator 5 a target current value i _{target can be} specified. The first control device 9 is set up, one above the shunt 10 to measure falling shunt voltage us and from this and a resistance value of the shunt 10 the one through the current loop 4th to determine flowing loop current i _O.

The current regulator 5 has a current control circuit, including in particular the series transistor 7th , the amplifier 8th , the first control device 9 , the shunt 10 and the field device 3 belong. The first control device 9 and thus the current regulator 5 is set up to regulate the loop current i _O to the setpoint current value i _setpoint . The current control loop has a first ring gain v _{R, 1} . Is the one from the The loop current i _O determined by the shunt voltage us is less than the desired current value i _Soll , then that of the emitter becomes the base of the series transistor 7th decreasing voltage increases. This is done by using the electrical potential of the output of the amplifier 8th is lowered. The amplifier 8th is accordingly from the first control device 9 controlled. If the determined loop current i _{O is} greater than the desired current value i _Soll , then the potential of the output of the amplifier 8th elevated.

The voltage regulator 6th has a transverse transistor 11 and a second control device 12 on. The cross transistor 11 is in the voltage regulator 6th arranged as a current sink for discharging a predeterminable part of the loop current i _O. The second control device 12 and thus the voltage regulator 6th a _target voltage value u _{target can be} specified. The voltage regulator 6th has a voltage control loop, including in particular the cross transistor 11 heard. The voltage control loop has a second ring gain v _{R, 2} . Next is the second control device 12 and with it the voltage regulator 6th set up a series voltage u _L across the series transistor 7th to regulate to the _target voltage value u _Soll by deriving part of the loop current i _O. The second control device is for this purpose 12 formed, the series voltage u _L across the series transistor 7th , so between its emitter and collector, to measure and the cross transistor 11 to be controlled accordingly. The cross transistor 11 is so with the current loop 4th connected that it is electrically parallel to the field device 3 lies. The cross transistor 11 is designed as an npn transistor. When the series voltage u _L across the series transistor 7th is less than the _setpoint voltage value u _setpoint , then the second control device controls 12 the cross transistor 11 at its base (third connection) in such a way that a current flow through the transverse transistor 11 between its collector (second connection) and emitter (first connection becomes lower, as a result of which the longitudinal voltage u _L increases. If the longitudinal voltage u _{L is} too high, the second control device controls 12 the cross transistor 11 in such a way that the current flow increases, as a result of which the longitudinal voltage u _{L is} lower.

The series transistor 7th has a first transistor output impedance at its collector Z _{O, 1} and the cross transistor 11 a second transistor output impedance at its collector Z _{O, 2} on. Both the collector of the series transistor 7th as well as the collector of the transverse transistor 11 are with the same node of the power source device 1 connected so that an output impedance Z _O is formed by the first and the second transistor output impedance. With a current output 12 . The output impedance Z _O is therefore at the current output 12 on.

The amplifier 8th is arranged and set up in the current control loop so that at least the first ring gain v _{R, 1 of} the current control loop is increased. Due to the increased first ring gain v _{R, 1} is an amount of the output impedance Z _O with a series voltage u _L known from the prior art across the series transistor 7th enlarged. In the present exemplary embodiment, the _setpoint voltage value u _{setpoint is} now reduced in such a way that the amount of the output impedance Z _O at a reduced nominal voltage value u _nominal across the series transistor 7th the amount of the output impedance Z _O at the series voltage u _L across the series transistor 7th and without amplifier 8th corresponds. Thus, the power loss of the power source device 1 and the transmission of HART signals in particular is unaffected. At this nominal voltage value u _nominal the series transistor work 7th and the cross transistor 11 in normal operation.

The current control loop and the voltage control loop are set up so that a ring bandwidth of the first ring gain v _{R, 1} and a ring bandwidth of the second ring gain v _{R, 2} include frequencies of HART signals. As a result, the ring bandwidths are greater than 2.2 kHz. In the present case, the current control loop was set up by the amplifier 8th has been set up in such a way that an amplifier bandwidth of the amplifier 8th includes the frequencies of HART signals.

In this embodiment, the shunt 10 an additional feedback device within a feedback of the current control loop.

There are also HART signals from the first control device 9 can be supplied and are fed through this into the amplifier 8th for amplification before the HART signals are transmitted into the current loop 4th fed in.

List of reference symbols

1

Power source

2

Supply voltage source

3

Field device

4th

Current loop

5

Current regulator

6th

Voltage regulator

7th

Series transistor

8th

amplifier

9

first control device

10

Shunt

11

Cross transistor

12

second control device

13

Current output

i _O

Loop current

i _should

Target current value of the loop current

U ₀

Supply voltage

u _L

Line voltage across the series transistor

u _S

Shunt voltage

u _should

Target voltage value via the series transistor

v

Amplification of the amplifier

v _{R, 1}

first ring gain (current control loop)

v _{R, 1}

second ring gain (voltage control loop)

Z _O

Output impedance

Z _{O, 1}

first transistor output impedance

Z _{O, 2}

second transistor output impedance

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Non-patent literature cited

• DIN IEC 60381-1 [0004]

Claims (11)

Current source device (1) for arrangement in a current loop (4) with a current regulator (5), a transverse transistor (11) and a current output (13) with an output impedance (Z _O ), the current regulator (5) having a nominal current value (i _nominal ) can be predetermined and the current regulator (5) has a series transistor (7), the series transistor (7) being arranged in the current source device (1) as a current source for impressing a loop current (i _O ) in the current loop (4), the current regulator ( 5) has a current control loop and is set up to regulate the loop current (i _O ) to the desired current value (i _Soll ), the series transistor (7) being in the current control loop and the current control loop having a first ring gain (v _{R, 1} ), the Cross transistor (11) is arranged in the current source device (1) as a current sink for discharging a predeterminable part of the loop current (i _O ), and the series transistor (7) has a first transistor output impedance (Z _{O, 1} ) and the Cross transistor (11) have a second transistor output impedance (Z _{O, 2} ) and the first transistor output impedance (Z _{O , 1} ) and the second transistor output impedance (Z _{O , 2} ) form the output impedance (Z _O ), characterized in that the current source device (1 ) has a voltage regulator (6) that the voltage regulator (6) can be given a nominal voltage value (u _Soll ) and the voltage regulator (6) has the transverse transistor (11) that the voltage regulator (6) has a voltage control loop and is set up, a longitudinal voltage (u _L ) via the series transistor (7) to the nominal voltage value (u _Soll ) by diverting part of the loop current (i _O ) to regulate that the transverse transistor (11) is in the voltage control loop and the voltage control loop has a second ring gain (v _{R, 2} ) has that an amplifier (8) with a gain (v) for increasing the first ring gain (v _{R, 1} ) is arranged in the current control loop. Power source device (1) according to Claim 1 , characterized in that the nominal voltage value (u _nominal ) is specified in such a way that the series transistor (7) is in normal operation. Power source device (1) according to Claim 1 or 2 , characterized in that the first ring gain (v _{R, 1} ) and the second ring gain (v _{R, 2} ) are set such that the output impedance (Z _O ) has a predetermined output impedance value (Z _{O, Soll} ). Power source device (1) according to Claim 3 , characterized in that the output impedance value (Z _{O, target} ) satisfies a HART specification. Power source device (1) according to Claim 3 or 4th , characterized in that the first ring gain (v _{R, 1} ) is set by the gain (v) of the amplifier (8). Power source device (1) according to one of the Claims 1 to 5 , characterized in that the amplifier (8) is arranged in the current regulator (5) for controlling the series transistor (7). Power source device (1) according to one of the Claims 1 to 6th , characterized in that the series transistor (7) is designed as a bipolar transistor. Power source device (1) according to one of the Claims 1 to 7th , characterized in that the current control loop and the voltage control loop are set up such that a ring bandwidth of the first ring gain (v _{R, 1} ) and a ring bandwidth of the second ring gain (v _{R, 2} ) include frequencies of HART signals. Power source device (1) according to Claim 8 , characterized in that the amplifier (8) is set up in such a way that an amplifier bandwidth of the amplifier (8) includes the frequencies of HART signals. Power source device (1) according to one of the Claims 1 to 9 , characterized in that a feedback in the current control loop is set up on the gain (v) of the amplifier (8) so that the ring bandwidth includes the frequencies of HART signals. Power source device (1) according to Claim 10 , characterized in that the feedback is frequency dependent.

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