Vibration Sensors play a crucial role in protecting and monitoring a plant machinery or a structure. These measurements help in controlling the process control systems and make adjustments in a process environment. These sensors can be found everywhere including aerospace labs and automotive test bays, to smart structures providing condition monitoring systems and active control.
But, how to ensure that the actual process value is measured by the sensor and passed along for processing?
While these sensors continue to improve the performance of processes, machinery and structures, they also tend to grow a calibration liability with time. During a sensor’s life cycle, either at time of manufacturing or in a test, a sensor must be calibrated to get the best possible accuracy out of it. Without proper calibration to a known acceleration standard, an accelerometer’s output cannot be verified and trusted.
Errors in vibration measurement can also occur due to mechanical wear or damage to the sensor. These types of errors usually require repair or replacement of the sensor.
Calibration involves finding out the deviation between the true reading and the displayed reading. It is the procedure of comparing the output from the sensor to a reference or standard value of high accuracy. In fact, many sensor manufacturers provide the recommended calibration periods in their product specifications.
In order to provide accurate data, accelerometers are calibrated to ensure they cover the correct frequency range and their sensitivity to acceleration is correctly rated.
Why Calibration Matters?
Any application that uses sensors requires correct sensor calibration to maintain accuracy in measurement. Calibration is mainly performed for the following reasons:
Increases Life of the sensor
The accuracy of any measuring device goes down with time due to external and working conditions. Calibrating a vibration sensor that’s giving inaccurate reading helps you set the sensor back to its original standard, without having to actually replace it.
Saves Cost
The errors produced by vibration sensors can get costly in the long run. For instance, when used for condition monitoring, if wrong data is logged, it could cause costly repairs or machine shutdowns. Manufacturers who don’t calibrate their sensors would end up with errors that create unusable parts. Also, research labs can end up with meaningless results because they were based on inaccurate measurements.
Without proper calibration, there would often be a need for halting and restarting processes when inaccuracies are discovered. The longer it takes for those inaccuracies to get noticed, the more costly the mistake will be. But if you always calibrate, you won’t have these problems.
Environmental Conditions
As sensors age over time, their response naturally changes too, mainly due to exposure to different environmental conditions.Especially for sensors that deal with potentially dangerous situations, like gas monitoring, sensor calibration can help prevent a catastrophe. Sensors expose themselves to aspects of climate and materials that can degrade its accuracy, making calibration an essential process. This is why they require periodic re-calibration.
How Sensor Calibration is Performed?
To perform calibration, a vibration sensor is exposed to a precisely defined excitation quantity and the measurements are recorded during this time. In order to measure something, the exact properties of the measuring equipment must be known. To ensure that, the measurement results are comparable with the measurements of third parties. The measuring instrument must be traced back to a national standard, wherein this traceability is regulated and secured by the calibration hierarchy.
Traceability shows that an instrument has been calibrated or certified by a higher-order standard which is then calibrated by its higher-order, and so on. A vibration sensor is generally calibrated and traced through a comparison method.
In order to take precise and commensurable measurements, the sensor can be calibrated in regular intervals by an accredited calibration laboratory or can be performed by the end-users using a traced calibration system.
