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WHEN TO CALIBRATE in a workshop
In today’s process industry, the field instruments are often calibrated out in the field. To do so, portable calibration equipment is used. Field calibration is often best but there are still various reasons why it is sometimes more convenient and effective to do calibration in a workshop. Beamex comments
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electing between field calibration and workshop calibration is not a
black-and-white situation. These two methods are not exclusive alternatives; instead, they complement each other. Beamex has previously presented the arguments for doing calibration out in the field, but this paper will discuss some of the most common reasons for establishing a workshop and doing the calibrations, or some of them, in the workshop with dedicated workshop calibration equipment.
1. COMMISSIONING One of the most common reasons to calibrate in a workshop is during the commissioning of a new plant, or some new parts of the plant. During the commissioning, the field equipment is not yet installed as the installation of the process equipment is not completed. The process equipment has typically already been purchased and is in storage in large quantities, 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 OF THE CALIBRATION The accuracy of the field instrumentation has been getting better and better during recent years, and this sets more requirements for the calibration equipment and also for all of the calibration processes. 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 controlled conditions.
3. PRIMARY STANDARDS IN A WORKSHOP As mentioned in the beginning, workshop calibration and field calibration 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/ ROTATING SPARES 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.
5. SAFETY 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, ESD protection.
6. ACCREDITATION AND QUALITY SYSTEM In some cases it is necessary or beneficial
/ PROCESS&CONTROL
The MCS 200 calibration bench
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PROCESS & CONTROL | JUNE 2015 S5
Beamex’s MCS 200 calibration workshop
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. FIELD CONDITIONS VS. WORKSHOP 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, ERGONOMICS, 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: • All equipment is always in place and ready to be used. All connections can be readily made and ready for use. • Panel-mounted, mains-operated equipment never has empty batteries that need to be charged before work. • Equipment never gets lost; it is always where it should be.
• All the equipment is optimally located for an ergonomic work space. The height of the bench tables can be motor controlled so it is easy to adjust ergonomic height for any work. • Panel-mounted automatic or manual pressure generation modules are ready for use, so there is no need to use manual pressure hand pumps. • The workshop offers more convenient work environment for the workers. The field conditions may sometimes be very harsh to work in.
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