Instrumentation calibration best practices, benefits

In a perfect world, process instruments would function in a facility just as well as the day they left the factory. The realities of operating a busy facility – environmental factors, equipment malfunctions, etc. – make this impossible, but instrumentation calibration can help a plant meet stringent calibration verifications and certifications.
Most plants conduct instrumentation calibration during annual shutdowns. If companies forget to schedule this vital service, consequences could range from annoying to dire.

Safety, accuracy: Instrument calibration

Why is instrumentation calibration important?

Making sure sensors and instruments are working correctly isn’t just a matter of production and uptime – it can mean life and death. Failure to calibrate air monitoring, flow, level, pressure, and temperature equipment properly could result in unsafe operating conditions, product quality issues, explosions, gas leaks, etc.

It’s also important for the bottom line. Accurate readings lead to better-functioning facilities and downtime decreases while product quality goes up. Which sensors need calibrating depends on the facility, but the most common instruments checked are pressure, temperature, flow, level and gas detection sensors.

Four instrumentation calibration best practices

Every plant has unique processes and applications, but instrumentation calibration is always a smart business decision. Four best practices for instrumentation calibration can help keep plants running safely.

1. Don’t wait to calibrate.

While calibration frequency is often client determined, many plants have instruments calibrated annually. Critical devices that affect plant safety, however, should be calibrated quarterly. A good example would be fixed gas detectors; it’s crucial to check these more often since failure could lead to hazardous conditions or even explosions. Companies also should consider sometimes scheduling instrumentation calibration outside of the annual shutdown period. Technicians can gain useful information from testing the control system and interlocks associated with these devices. While this choice comes with the added need to ensure bypasses are in place, it provides the ability to check this equipment during normal operation.

2. Keep checking the sensors.

It’s never a good idea to “set it and forget it,” not because sensors are unreliable, but because there are so many variables that affect the sensors’ measuring ability. For example, the physical installation may be causing erroneous signals or noise in the system. The programmable logic controller/distributed control system (PLC/DCS) scaling of the device may not match how the device is set up. These variables should be checked by simulating the device’s output when calibrating it. Sensors don’t have an expiration date, but calibrating at timed intervals is wise because users can catch issues sooner and improve reliability.

3. Document sensor calibration efforts.

To achieve the necessary certifications and verification standards, the right paperwork needs to be on hand. Make sure calibration technicians document their work and labeling accurately.

4. Choose an experienced calibration partner.

Choose skilled experts to do instrumentation calibration to ensure it’s done right. They should check each device against NIST-traceable reference equipment and adjust as necessary. For devices that don’t require calibration or can’t be easily field calibrated, verify the device is in good working condition and is properly communicating with the control system.

Three instrumentation calibration benefits

Regular instrumentation calibration benefits a plant in three main ways:

1. Compliance – Certain insurance providers, organizations, and governing bodies require certifications and verifications.

• California Air Resources Board (CARB) requires calibrations in ethanol and renewable energy facilities to sell products to the state of California
• Environmental sensors on water discharge and air discharge (baghouses vents) are sometimes required for environmental reasons
• Facilities with process safety management (PSM) require checking sensors critical to their process
• Facilities that process food must comply with Food and Drug Administration (FDA) regulations.

2. Safety – Employees need to be kept safe and protected at work. Regular calibration promotes a safe, healthy workplace and can give peace of mind.

3. Quality – Companies need accurate measurements and data to make a high-quality, reliable product. If the temperature sensor measurement is off, what will that do to the final product?

What the calibration process looks like

During the annual shutdown or quarterly calibration check, a crew of instrumentation technicians comes to the site with certified equipment. The crew walks down the facility to determine instrument locations and begins removing them for calibration, which could include pressurizing or subjecting them to a temperature from a known reference to check accuracy. The crew then checks all signals back to the control system to ensure the system is properly reading and registering. The technicians then reinstall the instruments and return them to service so they are ready for plant start-up and another year of steady plant operation. The process generally can be completed in under a week, depending on the size of the facility.

The company chosen for instrumentation calibration should be able to handle the entire process, from calibration plans to custody transfer certifications and documentation.

Adam Dittbenner is instrumentation manager at Interstates, a CFE Media and Technology content partner. Edited by Chris Vavra, web content manager, Control Engineering, CFE Media and Technology, cvavra@cfemedia.com

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