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Current Loop Circuits
Last Updated on:
Friday, October 16, 2009 03:41 AM |
| Circuits Designed by Dave
Johnson, P.E. : |
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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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Links to electronic circuits,
electronic schematics, designs for engineers, hobbyists, students & inventors:
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Circuit provides 4 to 20 mA loop for microControllers - 05/27/04 EDN-Design
Ideas: 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. Interfacing a 4- to 20-mA output to
a rudimentary microcontroller can be problematic.....(design idea added 1/05) |
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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.....(design idea added 6/06) |
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Current Loop Converter - Two Channel Isolated Industrial Version, schematic in
PDF format (added 4/02) |
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Current Loop Interface - (circuit added 7/02) |
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Loop powers Current transmitter - 10/28/99 EDN-Design Ideas:.....(design idea
added 2/06) |
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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) |
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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. ….(designed by David A.
Johnson) |
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Selectable Range Current Loop - Maxim Application Notes / 1085 / Aug-08
(app note added 5/08) |
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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. ….(designed by David A. Johnson) |
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