4-20ma source?

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PCEC

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B.C. Canada eh.
I used to have a 4-20ma source generator but it was dropped in a sewage lift station wet well so there it will sit for the foreseeable future. It was very handy for trouble shooting analog input loops to a plc. I'm about to troubleshoot a well level transmitter to a Scada Pack PLC and sure wish I had it handy. Does anyone have any suggestions for a simple 4-20ma loop signal generator or other ways to easily test the PLC input and/or the level transmitter?
 
Look at Fluke 77x source generators. I have a 773 and find it very useful because of the sourcing and measuring functions.


PCEC said:
I used to have a 4-20ma source generator but it was dropped in a sewage lift station wet well so there it will sit for the foreseeable future. It was very handy for trouble shooting analog input loops to a plc. I'm about to troubleshoot a well level transmitter to a Scada Pack PLC and sure wish I had it handy. Does anyone have any suggestions for a simple 4-20ma loop signal generator or other ways to easily test the PLC input and/or the level transmitter?
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Two 9VDC

Two 9VDC

Two 9VDC batteries, in series, will provide enough voltage to drive a simple 4-20mA loop. I am assuming you will go from batteries to transducer to multimeter and back to batteries.
 
140509-2123 EDT

An LM 317 in combination with a series combination of a 40 ohm fixed resistor in series with a 250 ohm variable Helipot should provide a good constant current load, or combined with a voltage source a constant current source.

On a sample with 249 ohms as the set point I had 5.00 mA from about 4 V to 14 V. From 14 to 30 V it gradually dropped to 4.86 mA.

Different 317 samples will have a slight variation in the output current for a given value of resistance. This is a function of the difference of the internal roughly 1.25 V reference. The variation in current vs applied voltage will vary somewhat from sample to sample.

See figure 4 of TI datasheet for current regulator circuit.
 
beanland said:
Two 9VDC batteries, in series, will provide enough voltage to drive a simple 4-20mA loop. I am assuming you will go from batteries to transducer to multimeter and back to batteries.
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Typically, yes. (Said typically as a disclaimer :eek:hmy:)

Note some transmitters will require 3 batteries in series... depends on the transmitters minimum operating voltage.
 
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