AGT 34420A w RTD Calibration Problems

Started by Hawaii596, 12-11-2018 -- 15:29:15

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Hawaii596

12-11-2018 -- 15:29:15
I am guessing this is where I should post thermodynamic questions...

I am pretty irritated with the HP/AGT 34420A RTD function.  When calibrating RTD's you have the choice of the RTD mode (reads temp only), or per OEM instructions, measuring the associated ohms in LP Ohms (low current). The 34420A has three Ohms modes: Normal, Low Current, or Low Volt Limited. The Low Current is the prescribed for measuring ohms on an RTD in preparation for running coefficient software. 

Problem is that RTD mode on the 34420A uses a 5 Hz AC low current technique in TEMP mode, but a DC low current in Ohms Mode. I cal RTD's with my Fluke 8508A with no problem in RTD mode, as it reads ohms value also. And my coefficients come out fine. But with the 34420A, as far as I can tell, there is no way to measure ohm values using the RTD technique. So when I finish measuring the various Ohms at the various applied temperatures, and run coefficients, I get inaccurate values. Running the same technique on an 8508A, I get within a couple of milliKelvin or so - good numbers. But on the 34420A, I get considerable errors (up to 0.02 Deg C or so). I have even thought of buying a 34420A input connector, and fabricating a really good solid copper, low thermal set of connections so that I can connect my 34420A type RTD's into an 8508A for calibration.

Anyone had this experience that can enlighten me?
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind."
Lord Kelvin (1824-1907)
from lecture to the Institute of Civil Engineers, 3 May 1883
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