Bench test 4-20ma strain gauge transmitter

bravloue · Feb 8, 2010

I have 3 strain gauge transmitters I need to bench test the 4-20ma output. The transmitter 4-20 side is two wire with a shield. I do have a known workiing strain gauge.

I have read several posts on how to create a 4-20ma signal with batteries, resistors etc. Can I test the 4-20 output using a standard DMM, batteries or a power supply to create the current loop?

nonuke · Feb 8, 2010

If the 4-20mA output is active, you just connect the DMM across the loop.
If the 4-20mA output is passive, you power the current loop with a power supply and connect the DMM in series with the circuit.

bravloue · Feb 8, 2010

I was told it was passive becuase it is 2 wire, supposed to be active if it is 4 wire? If I need to power the loop do you know how many volts power supply?

James Mcquade · Feb 8, 2010

we use a fluke 725 process calibration meter.
it will measure & generate ma's, volts, and t/c signals.

regards,
james

bravloue · Feb 8, 2010

Thanks for the info. I was hoping to do the test with a standard DMM.

TConnolly · Feb 8, 2010

Connect the transmitter to a power supply with a 250 ohm resistor. You can then either measure the voltage across the resistor, which will be 1V at 4ma and 5V at 20mA (mA= v/250), or you can put a milliamp meter inline with the circuit.



                         +-----+

+24V --------------------|     |

                         |     |

0V    -----\/\/\/\/\-----|     |

            250 ohm      +-----+

shooter · Feb 9, 2010

alaric is good however you can use a small battery of 9 volt when it is only short time. You can use your DMM also as a amp reader direct in the line.

Roy Matson · Feb 10, 2010

Shooters 9V battery may not be enough to power up the strain gauge, certainly not with 250 Ohms in series. It should tell you in the specs for transducer wghat load it will handle.
Alarics diagram is good but you don't need the 250 Ohms if you have mA meter.
Roy

bravloue · Feb 18, 2010

As I was about to perform the bench test with the 9V battery I was called away on a business trip and have not been home since. The transmitter does power the strain gauge but not the 4 - 20 loop.

Bench test 4-20ma strain gauge transmitter

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