When Control first took up the topic of calibration, it was still common practice to tune instrumentation on a fixed schedule, often with the aid of specially trained staff instrument technicians and an expensively equipped and dedicated lab area for applying simulated conditions and taking accurate measurements.
In June 1990, we reported how smart calibrators linked to an instrument database had streamlined the procedures at St. Johns River Power Park, a coal-fired power plant northeast of Jacksonville, Fla. The programmable calibrators from Loveland Controls could download an instrument’s identifying information and standard test procedure from a PC-based data manager, and automatically test the instrument to see if it was in spec. After the technician performed any needed adjustments, the as-left results were uploaded to the PC database.
In the field, the bench-top-sized calibrator was carried in a canvas sling with a padded shoulder belt. It connected to the IBM PC via RS-232 and carried test information and data through a shift with 136K of onboard memory.
Since then, as shown in the accompanying timeline, we’ve chronicled significant progress in calibration automation, data management and calibrator portability, capabilities and costs. More stable instruments and self-diagnostics have extended calibration intervals and allow us to predict when to calibrate.
Will Calibration Become a Lost Art?
Going forward, we can expect increasingly inexpensive, accurate and reliable instrumentation to be used for checking and verifying calibration. In August, 2012, Greg McMillan wrote, "I see an opportunity to use wireless instruments to do spot checks that would automatically get the data into an asset management system. If an additional pressure, temperature or electrode process connection is provided, a wireless transmitter verified in the shop can be used as the precision measurement for the spot check.”
Instrumentation may be applied in redundant configurations to make calibration unnecessary: Any sensor or transducer that’s out of step with its coworkers can be considered to have failed and simply be replaced at the next convenient opportunity.
Calibrators will be connected to the cloud so the status of instrumentation everywhere can be collected, aggregated and analyzed for trends or potential problems, both by end users and instrumentation manufacturers. Those web-enabled calibrators can themselves be monitored and verified to ensure accuracy and for regulatory compliance.
Meanwhile, many plants remain without even the modern equivalent of that system installed at St. Johns power plant in 1990. "Many plants calibrate devices at fixed intervals, but that’s less than optimal for a number of reasons,” wrote Dan Hebert, just last March. "Calibrating each device only as needed is the better method, and that requires automating the calibration process. Smart devices can provide information to an asset management system (AMS) or a calibration management system (CMS) over a digital data link. These systems use this information to determine optimal calibration intervals. They also send data to documenting calibrators, which are used to calibrate the devices. After calibration, these calibrators upload the 'as left’ condition of the device to the system.”
That’s a good place to start.