Current Loop Electronic Circuits

Current Loop Circuits
Last Updated on: Monday, October 03, 2011 06:07 PM

Circuits Designed by Dave Johnson, P.E. :

4-20ma Current Loop Tester:
Using just a few components, this circuit can simulate signals from various instruments, which source a constant current.

Low Value Capacitance Meter:
This circuit was originally designed to measure the volume of fluid inside a medical syringe. As designed, it produces a zero to 5 volt output, corresponding to a capacitance change of about 10 picofarads. With a digital voltmeter, at its output, it can resolve a capacitance change of 0.002 picofarads or 2 femtofarads.....

Pump Motor Monitor
This circuit can turn on a light or sound a beeper, whenever an AC line powered pump motor turns on. It is designed to detect the motor current using a small inductor placed on the outside of the motor’s power cable. No direct wire contact is needed.

TEMPERATURE SENSOR WITH 4 TO 20mA CURRENT LOOP
I designed a circuit similar to this one years ago to accurately measure the air temperature inside a building 1000s of feet from a control room. The circuit uses a very robust current loop method. It uses a highly accurate semiconductor temperature sensor and an equally accurate voltage reference. The circuit includes a diode bridge, so it is polarity independent. By using the component values indicated, the circuit should not require calibration. It has a range from –40F to +120F and an accuracy of +/- one degree F.

Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

3V/ 5V DACs Support Intelligent Current Loop - Maxim Application Notes / 722 / Jul-03.....[App Note]

A 4- to 20-mA loop needs no external power source - 09/13/01 EDN-Design Ideas.....The simple circuit in Figure 1 uses a low-current-drain MAX4073H amplifier to sense the current flowing through a 4- to 20-mA loop.... [Design Idea by Shyam Tiwari, Sensors Private Ltd, Gwalior, India]

4-20ma Current Loop Tester - Using just a few components, this circuit can simulate signals from various instruments, which source a constant current....[Designed by David A. Johnson]

Add fault protection to a 4- to 20-mA loop supply - 22-Jan-04 Issue of EDN A 4- to 20-mA current loop consists of a power source and a current-measuring device at the control end and a field transmitter that senses ..... [Design Idea by Mark Pearson, Maxim Integrated Products, Sunnyvale, CA]

Circuit provides 4 to 20 mA loop for microcontrollers - 27-May-04 Issue of EDN The 4- to 20-mA current loop is ubiquitous in the world of controls in manufacturing plants. Discrete logic, microprocessors, and microcontrollers easily cover the digital portions of control schemes.... [Design Idea by Robert Most, Dow Corning Corp, Auburn, MI]

Circuit Translates TTY Current Loop to RS232C - 08/03/98 EDN-Design Ideas.....Provides signal translation between a passive current-loop (TTY]interface and a duplex RS-232C ports.…Multiple circuits in this file…. [Design Idea by Jerzy Chrzaszcz, Warsaw University, Poland]

Current Loop Converter - Two Channel Isolated Industrial Version, schematic in PDF format (added 4/02)

Current Loop Interface - .....

Loop powers Current transmitter - 10/28/99 EDN-Design Ideas EDN is migrating links. This link is not verified. Search the "title" EDN for new link.

Low Value Capacitance Meter - This circuit was originally designed to measure the volume of fluid inside a medical syringe. As designed, it produces a zero to 5 volt output, corresponding to a capacitance change of about 10 picofarads. With a digital voltmeter, at its output, it can resolve a capacitance change of 0.002 picofarads or 2 femtofarads..... [Designed by David A. Johnson]

Pump Motor Monitor - This circuit can turn on a light or sound a beeper, whenever an AC line powered pump motor turns on. It is designed to detect the motor current using a small inductor placed on the outside of the motor’s power cable. No direct wire contact is needed..... [Designed by David A. Johnson]

Selectable Range Current Loop - Maxim Application Notes / 1085 / Aug-08.....[App Note]

Temperature Sensor with 4 to 20ma Current Loop - I designed a circuit similar to this one years ago to accurately measure the air temperature inside a building 1000s of feet from a control room. The circuit uses a very robust current loop method. It uses a highly accurate semiconductor temperature sensor and an equally accurate voltage reference. The circuit includes a diode bridge, so it is polarity independent. By using the component values indicated, the circuit should not require calibration. It has a range from –40F to +120F and an accuracy of +/- one degree F. …. [Designed by David A. Johnson]