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Current Loop Circuits
Last Updated on:
Wednesday, April 30, 2008 03:14 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.
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- 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.
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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.
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