In many process plants, keeping the operation running smoothly requires stringent calibration of hundreds of process control instruments. Consider all the different types of instrumentation that control vacuum and pressure, for instance. To maintain the highest level of accuracy and integrity, which has a direct correlation to quality of output, the pressure devices are calibrated as needed to ensure they are operating according to specifications.
Calibrating process instrumentation and documenting the results is vital to industries such as oil and gas, water, wastewater, chemical processing, pharmaceutical, food and beverage and even government scientific research labs.
Accuracy is vital
"Accuracy is vital for successful operation," a process control technician maintaining a prominent U.S. government lab said recently. "Our neutron beam facility, which consists of the linear accelerator, cryogenic plant and target facility, is operated by various software and process controls."
The facility has a variety of pressure devices to calibrate.
"We calibrate a number of pressure transducers, strain gauges, pressure switches and signal conditioning boards as part of new installations, preventive maintenance and troubleshooting," the lab technician said.
The lab, like many other facilities, has calibrated those devices using a documenting process calibrator. That calibrator worked well but involved using hand pumps to generate pressure, then finely adjusting and compensating for leaks. All that adjusting, when multiple calibrations are considered, ate up a lot of technician time.
To be sure, instrumentation technicians for years have talked about challenges with proper pressure calibrations. Generating the pressure, for one, required hand pumping. Leaks, in particular, are a challenge, requiring both dependable equipment and connectors.
Coping with leaks
A leaking pressure source makes it difficult to keep the pressure stable at a calibration point long enough to take a reliable reading. Technicians try to fine-tune and adjust pressure applied from a pump when there are slow leaks. Even after the desired pressure setpoint is reached, it is recommended that systems settle for several seconds or even minutes prior to testing so a more accurate and repeatable test result can be performed.
Steps a technician can take to ensure a better calibration experience include:
- Test and debug pressure test systems before entering the field to reduce unnecessary trips back to the shop.
- Try to decrease the number of pressure connections by using the correct hose length and removing extra fittings.
- Ensure test equipment is properly mounted.
- Mitigate leaks by using special-purpose test hoses.