A colleague recently asked a very important question:
How often should instruments be calibrated?
Many sites have requirements for calibration on certain instruments – such as fuel flow meters used for emissions reporting. But what about the rest?
Any sensor – temperature, pressure, flow, etc. – which provides input into your control system should be monitored regularly for accuracy. Things such as compressor inlet temperature, compressor discharge pressure and exhaust temperature – to begin with – all play a part in the load control of every type of gas turbine.
Annual calibrations are normally a good starting point – they provide you with a baseline for how each instrument changes over time. Reviewing these calibrations will give you a better understanding of how the working environment is impacting each sensor. In certain high stress applications – such as compressor discharge pressures on peaking units – calibrations and instrument adjustments may be needed more frequently than once a year. In low stress environments – such as cooling water temperatures – annual may be more than needed. But, if you lower the frequency of calibrations to less than annually, you may need to adjust your low-level alarm points to more readily catch instrument drift failures.
Please share how often you calibrate your site instrumentation here – I’d love to hear what your policies are. Do you calibrate all sensors or just a select few? Annually? Semi-annually (i.e. during each spring and fall outage)? Or “as needed”?
Do you utilize software tools, such as pattern recognition, to adjust your instrument calibration schedules?
I look forward to reading your replies.