A Bench Calibration is carried out in the shop at the bench with power supplied from an external source, if necessary. Bench calibrations might be performed upon receipt of new instruments prior to installation. This provides assurance the devices is received undamaged. This also allows configuration and calibration in a more good environment.
Various companies perform periodic calibrations on the bench. In this case the process instrument is removed from service, disconnected and taken to the shop for calibration. In some situations, a spare is installed in its place so the process downtime is minimized. For example, critical flow sensors might be sent out a specialized flow calibration facility. To prevent shutting the process down for several weeks, a replacement flow sensor would be installed.
Field calibrations are carried out "in-site", or in place, as installed. The instrument being calibrated isn't removed from the put in location. Field calibrations may be carried out after set up to ensure proper connections and configurations. Periodic calibrations are more likely to be carried out in the field.
Field calibrations are performed in the location in which the instrument operates. If the instrument is installed in a harsh location it is calibrated for that location. If the instrument is removed for a bench calibration and then returned, some error might be introduced due to the ambient conditions and orientation.
Advantages of Bench Calibration
- Removed, cleaned, inspected
- Better work environment
- Fixed calibration setup and utilities (electrical, air, vacuum) available
Advantages of Field Calibration
- May save time
- May identify and allow troubleshooting of installation problems
- Performed in actual ambient environment
