Raising the Bar for Accuracy

A more precise calibration method helps the RTC maintain the highest standard of data accuracy.

Author
Tiffany Burgess, Test Engineer
Date
August 1, 2016
Research Technician Becky Glover
performs a calibration at the TSPU

Arthur C. Nielsen, Jr. once said, “Watch every detail that affects the accuracy of your work.” At the RTC, we are striving to do just that! Reducing the uncertainty of measurements means more reliable data that lead to more reliable methods for our members.

Pressure drop across a heat exchanger can be several psid or just a few inH2Od (1 psid ˜ 27.7 inH2Od). While the differential pressure transmitters on each research rig are capable of detecting small values (0 – 25 in H2Od), the accuracy of our standard calibration equipment is best suited for larger pressure drops (0 – 25 psid), and the uncertainty can be as high as ±50% when operating at less than 10% of the instrument range.

After some reconfiguring of our vacuum-rated pressure calibrators, we developed a new method that dramatically reduces the uncertainty for small pressure drop values to under ±1%!

Research Technician Mike Holmes helps
Test Engineer Tiffany Burgess set up a
pressure calibrator

We previously used one calibrator with two channels: a 0 – 300 psia channel and a 0 – 50 psia channel. The new method uses two low-pressure, single-channel (0 – 7.5 psia) calibrators instead, and for applications with a substantially low pressure drop, the smaller span results in higher instrument accuracy.

Consider a standard double-pipe test section on the TSPU. For some conditions, a typical pressure drop across the test section is 10 psid. Using our previous calibration method, the uncertainty is ±0.51%, but measuring less than 1 psid results in an uncertainty of ±6%, which can be problematic because pressure drop often falls below 1 psid at lower flow rates.

 

With the new method, we can re-range and calibrate the pressure transmitters, reducing the uncertainty to only ±0.3% at 1 psid.

Maintaining a high standard of data accuracy is a priority at the RTC. After all, HTRI is the global leader in process heat transfer technology, not the ±50%!