The case for calibrating equipment in either a workshop or the field is not always black and white, writes Liz Fletcher from Beamex
In today’s process industry, instruments are often calibrated out in the field. To do so, portable calibration equipment is often used.
Field calibration equipment is often preferred, but there are still various reasons why it is sometimes more convenient and effective to do calibration in a workshop.
Beamex has previously presented arguments for doing calibration out in the field, but here we discuss some of the most common reasons for establishing a workshop and doing some calibrations there, using dedicated equipment.
One of the most common reasons to calibrate in a workshop is during the commissioning of a new plant, or new parts of an existing plant.
During the commissioning, the field equipment is not yet in place as the installation of the process equipment is not complete. The process equipment has typically already been purchased and in storage, waiting for installation. At that point it is very efficient to calibrate all the process equipment in the workshop before it is taken out into the field and installed. It is often faster and easier to calibrate all transmitters in the workshop prior to installation.
2. Total uncertainty
The accuracy of the field instrumentation has been getting better during recent years. The situation changes when the calibrations are done in the workshop with equipment and conditions dedicated for calibration work. In the calibration workshop, the calibration equipment does not have to be portable, but can be workshop equipment, which often has better performance than portable equipment. Also, the environmental conditions in the workshop can be controlled, so calibrations are always
performed in similar conditions.
3. Standards in a workshop
Workshop calibration and field calibration can complement each other.
There may be higher-accuracy, non- portable calibration equipment in the workshop as the primary reference calibration equipment. With these workshop primary standards, the portable field calibrators - which are used out in the field and of which there is often a larger number - can be calibrated.
4. Spare device calibration
In some cases it is more convenient to calibrate a spare device and then replace that into the process. That is especially the case when the calibration is difficult to do in the field, or the calibration takes a very long time to perform.
A professional calibration and service/ maintenance bench in a workshop can be equipped with proper safety facilities. This
includes items such as: isolation transformer, fault current protection, emergency switch, thermal overload protection, and electrostatic discharge protection.
6. Accreditation and quality
In some cases it is necessary to apply for an accreditation for the in-house calibration service performed. It is easier to get an accreditation for the calibration work performed in a dedicated workshop than it is for field calibration.
7. Working conditions
The field conditions may sometimes be challenging to work in.
Often the field is a hazardous area that sets requirements for the calibration equipment to be used, and not all calibration equipment is suitable for hazardous areas. For example, a temperature dry block cannot be used in hazardous areas, but it is still needed for temperature sensor calibration.
Often, instead of carrying several items of calibration equipment out to the field, it is easier to take the small device to be calibrated to the workshop, where all calibration equipment is ready for use.
8. Efficiency and ease of use
When doing the calibration in a workshop, the work can be arranged to be much easier and much more ergonomic than the work performed out in the field. Some of these considerations include:
• Equipment is always in place.
• Mains-operated equipment never has empty batteries.
• Panel-mounted pressure generation modules are ready for use, with no need to use manual pressure hand pumps.
Liz Fletcher is UK marketing manager at calibration supplier, Beamex.