Upper sensor trim

[MWTripper]

Anyone ever try performing an upper sensor trim on a PIT by applying the same stable process pressure to a calibrated pressure meter as is applied to the PIT? Say I have nothing available to apply a URV of 5000 psi to a PIT, but my process pressure is steady at 4223 PSI. My transmitter output indicates an error (say its output is 4000 PSI)so I use 4223 PSI as indicated on the calibrated meter as my applied pressure for the upper sensor trim,to correct the error.

 

[IRstuff]

A 5% error is a rather large error, don't you think, which might suggest that there is more than just a calibration problem?

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[danw2]

Interesting. I hope you try it and let us know.

The last time I did a 'wet' configuration [calibration] (10 years ago), by applying a pressure then specifying what the applied pressure value was, the transmitter set the URV (20mA) to that applied pressure value. I had no choice in the matter. Doing so changed the URV to the applied pressure value. I can't recall whose brand it was.

Here is Rosemount's statement for lower/upper trim:
Rosemount 3051S Series manual (page 80):

http://www2.emersonprocess.com/siteadmincenter/PM Rosemount Documents/00809-0100-4801.pdf

To calibrate the sensor with a Field Communicator using the sensor trim function, perform the following procedure:
1. Assemble and power the entire calibration system including a transmitter, Field Communicator, power supply, pressure input source, and readout device.
2. From the HOME screen, enter the fast key sequence under “Sensor Trim.”
3. Select 2: Lower sensor trim. The lower sensor trim value should be the sensor trim point that is closest to zero.
4. Follow the commands provided by the Field Communicator to complete the adjustment of the lower value.
5. Repeat the procedure for the upper value, replacing 2: Lower sensor trim with 3: Upper sensor trim in Step 3.

NOTE:
Select pressure input values so that lower and upper values are equal to or outside the 4 and 20 mA points. Do not attempt to obtain reverse output by reversing the high and low points. This can be done by going to “Rerange” on
page 3-9 of Section 3: Configuration. The transmitter allows approximately five percent deviation.

NOTE
The transmitter must be within three percent of true zero (zero-based) in order to calibrate with zero trim function.
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It isn't clear whether the applied pressures and values are a zero and span values between which read pressures are linearized or whether the URV is affected in any way. Since URV isn't mentioned, it might not. But then again, you might not have a Rosemount 3051.

In any event, can you isolate and bleed it to check zero?

What have you got to lose by trying a span trim?

 

[MWTripper]

IRstuff (Aerospace)
14 Dec 10 1:17
A 5% error is a rather large error, don't you think, which might suggest that there is more than just a calibration problem?

Well, I was wondering the same thing. Its a large error to find on a Rosemount 3051 that was factory calibrated and has been in service for maybe a year. I don't know any other history on this instrument save that it was only loop checked previously and that the error has existed for a while. I only looked at a few day trend.

Results:
Transmitter removed from the program logic, isolated and vented. Zero trim performed. Process pressure introduced. High sensor trim performed using stable process pressure of 4223 PSI (verified with 2 calibrated pressure meters). Transmitter isolated and pressure applied with very leaky high pressure pump to over 5000 psi and transmitter output monitored as pump leaked its way down. Pump up performed a few times and span error was reduced to approximately 4 PSI at the top. Impulse leg was filled and zero trim performed. Process pressure introduced. Transmitter placed back in service.