10 ohm Platinum RTD 1

I have only seen PT 100 or Cu 10 RTD's. For PT 100, the thumb rule is app 4 ohms every 10 degrees. So, I would guess it's 0.4 ohms every 10 deg with PT 10.

I have never seen 10 Ohm Pt, 10 Ohm Cu is very common for motor windings, I suspect the label is wrong.
Ooops I just found a reference to a 10 Ohm Birdcage model in Omega catalog
You should use the 3 wire method otherwise the interconnecting cable will give you errors.
If by any remote chance it is Pt you can look at the tables for 100 Ohm and divide by 10
e.g. 10 @ °C, 13.85 @ 100°C
Regards
Roy

On further research the values for 10 Ohm Cu would be very close to 10 Ohm Pt
Cu 9.035 @ 0, 12.897 @ 100 C or Delta 3.8625 Ohms
Pt 10 @ 0, 13.85 @ 100 C or Delta 3.85 Ohms
I don't think you will have any difficulty offsetting the zero to match Pt. Worst case you could add a little resistance.
So purchase a 10 Ohm Copper transducer, it may not be perfect but close enough for a motor

dpc
I've used this in the past although not for PT 10 but I see it can accept this input.

Thanks to all. They are definitely not 10 ohm copper. The problem is that these were connected to a temperature monitor unit based on 10 ohm copper RTDs. This unit has no calibration adjustments and provides discrete contact outputs at adjustable temperature setpoints as well as an analog output. We did find an IEC standard for 10 ohm platinum, as well a couple of other standards.

For the short term, we can set the trip setpoints to be correct at the trip temperature. I'm just looking for a longer-term off-the-shelf solution. We could replace the bearing RTDs without too much trouble, but the stator winding RTDs would be hard to replace.

Dave

ozmosis,

I did find the ABB model that can accept the Pt10 inputs - so that is definitely a possible solution.

This generator has been in service for about 15 years and apparently no one noticed (or cared) that the RTDs were not accurate.

You probably only care about a very narrow temperature range where action would be taken. I would calibrate at just that critical temperature.

Get a temp controller or an RTD calibrator that takes in a 10ohm CU RTD. Hook it to that spare PT RTD you have. Then toss it into a temperature space at your critical temperature point and see what reading you get. That would be the temperature you'd actually want to set your safety points at on your generator.

Keith Cress
kcress -

This outfit claims their RTD unit is good for RTDs from 6 - 6,000 Ohms


I think they are part of Omega

I have used indicators from Precision Digital, they have a multiplexer that can be used for RTDs
Use a Decade box for calibration, it's much quicker than heating/cooling a spare RTD
Roy