Calibration is the process of finding a relationship between two unknown quantities. When one of the quantities is known by way of a measurement device, another measurement is taken with a second device under similar conditions. The measurable quantities may be different in two devices that are otherwise equivalent. The device with the assigned correctness is called the standard. The second device is known as the unit under test.
Calibration ensures that the measuring device is consistent, accurate and reliable because a measurement used in decision making has to have a high level of accuracy. A well-calibrated device has a margin of error that is known and always taken into consideration. In order for calibration to be successful, a device must be able to “hold a calibration” throughout the calibration process, meaning it must be able to take measurements that are within engineering tolerances when used under the specified conditions over a reasonable period of time.
When Should Calibration Be Done?
Calibration is done under the following circumstances:
- When an instrument is new
- When an instrument undergoes repair or some modification
- Whenever a specified time or usage period has elapsed
- In some cases, before or after a crucial measurement
- After such events as vibration, shock or physical damage that can affect initial marksWhenever observations are doubtful
- Customers or instrument manufactures specify a requirement
There are several benefits to calibrating measurement devices. Calibration ensures reliable measurements so that measurements made in one facility are compatible with those made in another. It also ensures proper equipment maintenance. All devices age with time and may sustain mechanical wear and tear. Aging equipment can be replaced or repaired to ensure accuracy across all operations. Ultimately, calibration results in cost savings as it allows informed decision making that can reduce waste and rework.
The Process of Calibration
Readings obtained from the scale of an instrument are put together to see if they are in unison with readings of a standard, giving a calibration curve from the obtained values. The instrument is fed with some values already known obtained from the standard. The obtained output from the instrument is recorded and compared against original value and that of the standard.
There are four main steps to calibrating an instrument.
- The first step involves establishing a relationship between the test weights or standard and the unit under test. No assessment is done at this time. This step simply answers the question of how well the instrument is performing.
- The second step is assessment. In this step, it is determined whether or not the device falls within specified tolerances. A pass or fail statement is issued depending on whether or not the device operates well enough to meet requirements.
- Third, adjustments are made to the instrument so that measurement deviations are made as small as possible.
- Lastly, the instrument is recalibrated to confirm consistency since adjustment may alter the equipment parameters.
All calibration procedures follow this general outline. The method of testing and adjustment will depend on what type of device is undergoing calibration.
It is clear that calibration is absolutely necessary in order to comply with legal trade tolerances and even stricter standards that ensure efficient and profitable operations.
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