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Rosemount transmitters
How to resolve the SATURATION Problem on Rosemount Transmitters
By Amar DAMENE on 9 August, 2018 - 3:13 am

Dear all,

We just finish the commissioning of DCS project (a new compression gas station) and we are facing a SATURATION problem with many of our Rosemount transmitters.

PLease, how to resolve this problem

Thanks for sharing your experience

Nb : We do not have this problem with
Honeywell transmitters installed on Gas Turbine

Amar

Change to a higher range on both the transmitter and the DCS.

By W.L. Mostia on 9 August, 2018 - 2:17 pm

You need to be more specific in your problem description. Is your problem that the saturation levels are not what you want or something else? Did you specify the wrong ones when you brought the transmitters?

If you want help on this mail list, it helps to be specific! Do not assume that everyone will understand what you mean when you say that you're having a problem with SATURATION.

William (Bill) L. Mostia, Jr. PE
ISA Fellow, FS Eng. (TUV Rheinland)
WLM Engineering Co.
281-728-3722

By Amar DAMENE on 12 August, 2018 - 3:06 am

Dear William,

I will try to be more specific in my problem description.

My problem that the saturation levels are not what I want.

No I did not specify the wrong ones when we ordered the transmitters.

To be clear:
First, one transmitter was wrong and we had to change and buy a new one. After receiving the new transmitter, I checked the calibration certificate and it written that:

at 0.00 mbar 3.93148 mA Pass
at 250 mbar 19.99836 mA Pass

But after installation of the transmitter on the site, I observed on LCD of the transmitter:

ANALOG SATURATION
Delta P : 10 mbar

On DCS, the value of transmitter is out.

Trying to connect HART to see the values of saturation level, I find it to be 3.9 mA.

Hope this is clear.

Here's what the 3051 manual says about saturation level:

2.9.1 Configuring alarm and saturation levels
In normal operation, the transmitter will drive the output in response to pressure from the lower to upper saturation points. If the pressure goes outside the sensor limits, or if the output would be beyond the saturation points, the output will be limited to the associated saturation point.

3.9mA is the standard Rosemount low saturation/alarm output level (as opposed to 3.8mA for NAMUR or 3.7-3.9 for custom setup); 20.8mA is high.

I would conclude that you have an applied negative pressure driving the output into low saturation. Are you sure that the display is not reading Delta P: -10 mbar ?

Is the high side piped to the high side?
Is the low side piped to the low side?

If you disconnect the transmitter from the process so it 'sees' atmospheric pressure, does the output go to 4.0mA (0.0mBar)?

The calibration certificate does not guarantee what the LRV and URV settings are.

You need to check LRV and URV to make sure the 4-20mA output range is what you expect.

What does "value of the transmitter is out" mean? How is a numerical value "out"? Out of range? What range? Out-of-service?

By Amar DAMENE on 13 August, 2018 - 2:58 am

Dear all,

Yes, I agree with you.

I have read what the 3051 manual says about saturation level

To respond you about your questions :

No, I have not applied negative pressure.

Yes I am sure that the display is not reading Delta P: -10 mbar

Yes the high side piped to the high side
and the low side piped to the low side

If I disconnect the transmitter from the process so it
sees' atmospheric pressure, the output go to 4.0mA
(0.0mBar)

LRV 0 mbar
URV 250 mbar

The transmitter is out on DCS means there is not display of DELTA PRESSURE DISPLAYED

By W.L. Mostia on 13 August, 2018 - 12:03 pm

I would try the following to see if you can get any additional clues to help you out:

1. The fact that when you opened your ports to the atmosphere, the transmitter reads 0 mbar (4 mA) and your saturation signal goes away, but when connected reads some kind of pressure and saturation, leads to the conclusion that there is pressure at the ports. I would suggest that you place pressure gauges or a process calibrator at the ports to determine if there is pressure there and what it is.

2. Read the actual 4-20 A signal during this saturation and when the transmitter is zeroed.

3. Use a process calibrator on the transmitter and run a calibration to see it the transmitter is working properly.

4. Check where the diagnostic failure mode direction is set and whether you have any diagnostic statuses in the transmitter when you are reading saturation.

5. Replace the transmitter with one that is similarly calibrated to see if it works properly

William (Bill) L. Mostia, Jr. PE
ISA Fellow
WLM Engineering Co.
281-728-3722

What are you trying to measure? If it's level it could be the transmitter is actually saturated by an uneven process pressure.
250 mb is equivalent to about 2.5 meters WC.

Please post a sketch of your application with rough dimensions, vertical height from pressure taps to centerline of transmitter.

If it's a steam application, allowance must be made for vertical height, the steam will condense in the top connection requiring an offset range.