You know that calibration is required for a new instrument. We want that the instrument is provide accurate indication or output signal when it is installed. But there is chances of instrument error occurs.
Instrument error can occur due to a variety of factors: drift, environment, electrical supply, addition of components to the output loop, process changes, etc. Since a calibration is performed by comparing or applying a known signal to the instrument under test, errors are detected by performing a calibration.
An error is the algebraic difference between the indicated value and the actual value of the measured variable. Typical errors that occur are as given below.
- Span error
- Zero error
- Combined zero & span error
- Linearization error
Zero and span errors are corrected by performing a calibration. Most instruments are having facility for adjusting the zero and span of the instrument, along with instructions for performing this adjustment.
The zero adjustment is used to produce a parallel shift of the input-output curve. The span adjustment is used to change the slope of the input-output curve. Linearization error may be corrected if the instrument has a linearization adjustment. If the magnitude of the nonlinear error is unacceptable and it cannot be adjusted, the instrument must be replaced or repaired.
To detect and correct instrument error, periodic calibrations are performed. Even if a periodic calibration reveals the instrument is perfect and no adjustment is required, we would not have known that unless we performed the calibration. And even if adjustments are not required for several consecutive calibrations, we will still perform the calibration check at the next scheduled due date. Periodic calibrations to specified tolerances using approved procedures are an important element of any quality system.
Why we should calibrate?
- Testing a new instrument
- Testing an instrument after it has been repaired or modified
- Periodic testing of instruments
- Testing after the specific usage has elapsed
- Prior to and/or after a critical measurement
- When observations are not accurate or instrument indicators do not match the output of a surrogate instrument
- After events such as:
- An instrument has had a shock, vibration, or exposure to adverse conditions, which can put it out of calibration or damage it.
- Sudden weather changes
Risk Involved in Not Calibrating an Instrument
- Safety procedure: In case of instruments involving perishable products such as food or thermometers with area of sensitive nature, uncalibrated instruments may cause potential safety hazards.
- Wastage: If the instrument is not perfectly calibrated, it might lead to potential wastage of resources and time consumed in the operations, resulting in an overall increase in expenses.
- Faulty or Questionable Quality: If the instrument is improperly calibrated, the chances of faulty or questionable quality of finished goods arises. Calibration helps maintain the quality in production at different stages, which gets compromised if any discrepancy arises.
- Fines or litigations: Customers who have incurred damage may return the product against a full refund, which is still alright; but if they go for litigation due to damages, you could be up for serious costs in terms of reputation and restitution payments.
- Increased downtime: Poor quality of finished goods is the first indicator of disrepair in your equipment. Regular calibration programs identify warning signs early, allowing you to take action before any further damage is caused.