PineMarten,
I see that nobody has answered yet, I'll take a stab at it.
By your description, it sounds like you are opening the circuit completely so that the only thing in the loop during your test is the pressure transducer, the wire, and your fluke. Is this correct? If so, you can't do it that way.
You must test the signal with the recorder left in the circuit (circuit intact), and your fluke connected in series. This should be a series loop, current is always the same throughout a series circuit. The circuit impedance would be less with the recorder in the circuit, therefore current would be greater.
You've pretty much already ruled out any problem at the recorder by getting the same results on all 5 channels.
If you test the circuit with your fluke in series like described previously, both your fluke and the recorder should read the same value. If they don't, either your fluke or the recording interface is out of calibration.
You didn't say if the transducer in question was under any amount of pressure or not when you were testing it. I assume that this transducer is suppose to allow 4ma @ zero PSI, and 20ma @ its maximum PSI rating.
With the circuit connected just as it would be during operation, and zero pressure on the transducer, install your fluke in series. Your fluke and the recording interface should read 4ma. If it does not, the transducer is either out of calibration, or defective. Subjecting the transducer to an amount of pressure at half of its range, should result in a reading of approximately 8ma.
If you work with 4 to 20ma circuits often, it might pay for you to own a milliamp driver/tester. These instruments can drive a milliamp signal of your choice anywhere between 4 and 20 ma so that you can substitute it for the source in your circuit. This will prove if the value on your readout is accurate or not by comparing the readout to the signal driven by the tester. It could also help isolate problems in the 4 to 20ma source. Of course these instruments will also measure the signal just as your fluke does.
Matt
[This message has been edited by Matt M (edited 08-24-2003).]
