Calibration of intelligent differential pressure transmitters
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Although intelligent differential pressure transmitters have high precision, is actual calibration necessary? What are the methods for it? What should be the required accuracy levels for the input pressure and output signal readings? Is a pressure calibrator better, or is it better to use a single gauge connected through a circuit? How should this be done in engineering projects, and in school laboratories? I’d appreciate some advice!
We have also encountered this problem: the accuracy of the calibration tables used is lower than that of smart meters, and in theory it should be impossible to carry out calibration. Usually, we still use single-meter connection circuits for calibration; basically, as long as the input and output values match, the meter is considered to be working properly.
In a factory, it can generally be determined based on the operating conditions; whereas in a laboratory, the equipment’s precision requirements must be met
We now use pressure calibrators, and the accuracy of our standard instruments is quite high. Generally, we require an accuracy of 0.2 and 0.25 for field meters. Therefore, as long as the standard device can meet the requirements for calibrating meters of class 0.2, there is no need to consider the accuracy of the smart transmitter itself. The accuracy of modern smart meters can be adjusted to very high levels, but in practical use we do not require such high accuracy; calibration can be carried out based on actual conditions. For standard tables, the precision we usually use is 0.01
Although intelligent differential pressure transmitters have high precision (up to 0.075%), they can also suffer from issues such as zero drift and poor linearity; therefore, calibration is also necessary when there are suspicions of problems with the indication. The common verification method is to measure the output current under pressure. A few days ago, I tested a smart transmitter (used for measuring liquid levels), and its linearity was poor – when the input was zero, the output was also zero ； When a 50% pressure is applied (with the negative pressure side connected to atmospheric pressure), the error is the greatest, showing a liquid level of 50.6% ； And 100% pressure shows 100.2%.
Smart differential pressure transmitters offer very high accuracy; for example, the Rosemount 3051 can achieve 0.075% accuracy. We use such transmitters here, and I usually settle for the 744 model for my needs.
Upstairs, what is 744?
FULK744, a tool commonly used by instrument technicians.
For general calibration, the standard instrument needs to be two grades more precise than the instrument being used; if that’s not possible, the only option is to use a less precise instrument
Of course, calibration is also necessary; reference can be made to Volume 7 of the Maintenance and Repair Procedures for Petrochemical Equipment. As the accuracy level of instruments increases, whether high precision is required depends on the requirements of actual use. The higher the accuracy of an instrument, the higher the accuracy of the standard instruments used for calibration must be; some on-site calibration devices do not meet the requirements for calibrating instruments