Pt 100 on ABB Swirl Meter

I

Thread Starter

Inch man

I fell into a situation where I had to troubleshoot an ABB swirl meter on a steam application where clearly it was not giving the correct reading. It was deemed to be a Mass meter by virtue that it had temperature compensation via a Pt 100 sensor which was installed in the primary element. and when this was measured its resistance indicated a temperature significantly greater than what the steam pressure was (no it was not superheated).

A service engineer came and applied an offset in the transmitter electronics with the proviso that it may require further tweaking! I find this hard to believe that a Pt 100 which should correspond to accepted tables should require any sort of "fudge" factor please put my mind to rest.
 
R
I agree, a 100 Ohm Pt sensor should never drift.
Are you sure it's 100 Ohm
The manual and part No should spell it out.

Roy
 
I agree with your assessment of how close Pt100's are to their tables. But I've worked with the pharmas and seen their accumulated cal paperwork that shows that RTDs can drift over time. Maybe you've got a baddie.

Some other thoughts:

In the absence of model info, I looked at the current version Swirl meter manual,
http://tinyurl.com/853sxku

1) Out of curiosity, which of the operating modes have you selected?
Gas/steam medium:
- Mass flow with constant or temperature-dependent density (at constant pressure)
- Standard flow with constant or temperature-dependent standard factor (at constant pressure)
- Mass flow with saturated steam and temperature-driven density

There's no absolute pressure sensor on the swirl meter, so the calculated mass value assumes constant pressure. Is that the case in reality?

2) You must be using a steam table to determine that temperature reading is not correct according to the line pressure, correct? How good is the pressure reading you're using?

3) Is the RTD an ABB 4 wire RTD that is color coded to match the table in the manual, so the right wire gets to the right terminal?

If it's not an ABB 4 wire Pt100, does your site use the Burns 392 alpha RTDs rather than the DIN 389 alpha? A given temperature would have a higher resistance with a Burns alpha RTD.

4) The meter can display the fluid temperature. The tech's temperature check was "its resistance indicated a temperature significantly greater than what the steam pressure was".

Was the meter powered off when this resistance measurement was made so the meter's RTD circuit current pump was not feeding into the ohm meter's circuit when the resistance measurement was being taken?

5) This manual note, "At high media temperatures > 150 °C (302 °F), the flowmeter sensor must be installed so that the electronics are pointing to the side or downward" warns about baking the electronics. If the electronics are too hot, the circuit's temp coefficient could be giving high readings. The electronics aren't being cooked to death are they?
 
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