Saturation-controlled loop current regulator

Patent metadata

Field	Value
Publication number	US-2016291579-A1
Application number	US-201514672641-A
Country	US
Kind code	A1
Filing date	Mar 30, 2015
Priority date	Mar 30, 2015
Publication date	Oct 6, 2016
Grant date	—

Abstract

A process transmitter includes device circuitry that generates values that are to be conveyed on a current loop. A series control transistor is in series between the current loop and the device circuitry and a saturation prevention circuit prevents the series control transistor from entering saturation.

First claim

What is claimed is:

1 . A process transmitter comprising:
device circuitry that generates values that are to be conveyed on a current loop; a series control transistor in series between the current loop and the device circuitry; and a saturation prevention circuit that prevents the series control transistor from entering saturation.

2 . The process transmitter of claim 1 wherein the saturation prevention circuit prevents the series control transistor from entering saturation by preventing a voltage across the series control transistor from dropping below a saturation voltage.

3 . The process transmitter of claim 1 wherein the saturation prevention circuit maintains the voltage across the series control transistor so that the voltage is substantially equal to a forward bias voltage across a diode in the saturation prevention circuit.

4 . The process transmitter of claim 3 wherein the saturation prevention circuit comprises a shunt transistor having an emitter coupled to a collector of the series control transistor and a base coupled to a base of the series control transistor through a conduction path that includes the diode.

5 . The process transmitter of claim 4 wherein the emitter of the shunt transistor is connected directly to the collector of the series control transistor.

6 . The process transmitter of claim 5 wherein the conduction path between the base of the shunt transistor and the base of the series control transistor comprises three diodes.

7 . The process transmitter of claim 6 wherein at least two of the diodes are matched.

8 . The process transmitter of claim 4 wherein the series control transistor and the shunt transistor are matched so as to provide substantially similar base-emitter voltage drops.

9 . A process field device comprising:
control loop connectors for connection to a process control loop; device circuitry; and a current regulator in series between a control loop connector and the device circuitry wherein the current regulator controls a current level on the control loop and provides a power output that has a maximum power that scales with a voltage provided on the process control loop.

10 . The process field device of claim 9 wherein the current regulator comprises a series transistor and a bias circuit wherein the bias circuit of the series transistor prevents the series transistor from saturating.

11 . The process field device of claim 10 wherein the bias circuit prevents the series transistor from saturating by limiting a collector-emitter voltage across the series transistor from dropping below a forward bias voltage drop across a diode.

12 . The process field device of claim 11 wherein the bias circuit comprises a diode and a shunt transistor that shunts current away from the device circuitry.

13 . The process field device of claim 12 wherein the bias circuit further comprises circuit elements to prevent reverse breakdown of the shunt transistor.

14 . The process field device of claim 13 wherein the circuit element to prevent reverse breakdown of the shunt transistor comprises a second diode.

15 . The process field device of claim 13 wherein the anode of the diode is connected to the base of the series transistor, the cathode of the diode is connected to an anode of a third diode, the cathode of the third diode is connected to the cathode of the second diode and the anode of the second diode is connected to the base of the shunt transistor.

16 . The process field device of claim 9 further comprising a switching regulator in series between the current regulator and the device circuitry.

17 . A process field device comprising:
two loop connectors for connection to a current loop; device circuitry; and a current controller in series between one of the two loop connectors and the device circuitry wherein the current controller is capable of controlling a current level in the current loop while providing a fixed voltage drop between the current loop and the device circuitry for a plurality of current levels in the current loop.

18 . The process field device of claim 17 wherein the current controller is intrinsically prevented from providing a voltage drop that is less than the fixed voltage drop along a direction of the current of the current loop.

19 . The process field device of claim 17 wherein the current controller comprises a series transistor, a shunt transistor, and at least one diode such that the voltage drop between the current loop and the processing circuit is across the series transistor and the at least one diode and the shunt transistor intrinsically prevent the voltage drop across the series transistor from being less than a forward bias voltage across the at least one diode.

20 . The process field device of claim 19 wherein the current controller further comprises two additional diodes wherein one of the two additional diodes substantially prevents the shunt transistor from entering a reverse breakdown state.

21 . The process field device of claim 17 wherein the current controller comprises a series transistor, a shunt transistor, and an amplifier, wherein the amplifier is connected to the base of the shunt transistor and drives the shunt transistor to maintain the voltage drop across the series transistor.

22 . The process field device of claim 21 wherein the current controller further comprises a first voltage divider connected to the device circuitry and a second voltage divider connected to the current loop, wherein a non-inverting input of the amplifier is connected to the first voltage divider and an inverting input of the amplifier is connected to the second voltage divider.

23 . The process field device of claim 22 wherein the second voltage divider is connected to the current loop through a diode.

Assignees

• Rosemount Inc

Inventors

• Holmstadt Clarence Edward
• LaRoche Robert Ernest
• Mccoy Steven J

Classifications

• G05B19/414 Primary

  Structure of the control system, e.g. common controller or multiprocessor systems, interface to servo, programmable interface controller · CPC title

• G05B19/042 Primary

  using digital processors (G05B19/05 takes precedence) · CPC title

• G05B2219/25428

  Field device · CPC title

• G05B2219/31121

  Fielddevice, field controller, interface connected to fieldbus · CPC title

• G05B2219/41411

  Avoid integrator wind-up, saturation actuator by dead zone feedback for integral · CPC title