Lower trim on absolute pressure transmitter

Good day support team, many thanks in advance for your valuable feedback. Could you please help me with this technical clarification?

Target: Calibrate Absolute pressure transmitter (Hart) which has a range: 0 - 200 psia (absolute)

I would like to reinforce this point: from the Rosemount manual, a recommendation states: Do not perform a Zero trim on Absolute pressure transmitter (since they are reference to absolute zero, really difficult to reach).

If zero sensor trim is not highly recommended, a Lower sensor trim is an option to be performed. How Can I perform this Lower sensor trim in an absolute pressure transmitter without altering the factory curve?

This transmitter is installed at site which has an atmospheric pressure of 14.69 psig (provided by marine department). In addition to that, we can get the information by using an Absolute pressure module Fluke 700PA6 connected to the Fluke 754. From the Fluke the Atmospheric pressure is 14.74 psig. Considering that the Fluke is more accurate, so the considered atmospheric pressure will be 14.74 psig.

Is it correct to perform the:

Lower sensor trim at 14.74 psig and

Upper sensor trim at (200 -14.74) 185.26 psig

I just wonder if Both sensor trim could affect the curve (since from Factory, the first point was considered the Absolute zero).

Since, I have never done a Lower trim on Absolute pressure transmitter, if the Lower and Upper sensor trim is done, What happens with the initial range which is 0 - 200 psia?

Many thanks for your support and valuable feedback.

Kind regards,


2 Replies

  • In order to maintain the factory calibration, I suggest that you only perform a lower sensor trim.
    A lower sensor trim will shift the factory calibration curve to intercept the trim point but will not change the factory calibrated slope of the line.
    You need to reference a barometer to perform a lower sensor trim. The atmospheric pressure will generally be less than 14.7 psia unless you are close to or below sea level. Selection of the correct reference for trim will be important to make sure that your offset is as accurate as possible.

    Go ahead and contact me directly so we can figure out the best reference source for your case.
    Performing a lower and upper sensor trim will alter the factory calibration, which we can recover by recalling factory trim.
    Thank you!
  • In reply to Brad Burton:

    Hello Brad,
    Sorry for the delay, I have been working in a remote place. I really appreciate your knowledge sharing and clarification. It is clear to me after receiving your feedback. again, thank you so much!!!
    Kind regards,