At Procon we know how important it is for process weighing vessels to be calibrated on a regular basis, but also recognise that carrying this out in practice can be difficult, and at times disruptive. Although as a company we offer a range of recognised calibration methods selected to meet specific customer requirements, on-site operational conditions and locations can limit their use and effectiveness. To overcome these restrictions, we have developed our versatile Procon Force Cal™ calibration technique.
ForceCal is a well-proven, highly cost effective, non- intrusive calibration method that has a minimum affect on the plant process. It can be carried out quickly by a single engineer and is suitable for calibrating vessels from 800 kg up to 50,000 kg in capacity.
A leading industry expert has estimated that over 80% of process vessels in the UK do not have adequate calibration traceability. Inadequately calibrated vessels affect product quality, productivity and above all bottom line profitability. All too often, vessels are calibrated during initial commissioning and then the ongoing process and production schedules, together with the design and vessel location; limit the possibilities of carrying out further adequate calibration on a regular basis. In many cases, not being able to apply a suitable method throughout the measuring range results in partial calibration being carried out in difficult conditions with the obvious poor results.
Conventional methods typically require the vessel to be empty before the calibration is started. The most common methods of applying calibration loads to vessels are based around filling the vessel with a measured quantity of water using a flow meter or applying traceable test weights. Both these techniques require the vessels to be taken out of the production cycle for long periods of time and only enable a single calibration cycle to be carried out.
The flow meter method is a fully intrusive method requiring the availability of an adequate supply of clean water, together with a means of disposal. Not only is the calibration process a lengthy procedure, but in many applications there are no easy means of disposing of the water, which may be contaminated with process product. It is worth remembering that the costs associated with any cleaning and disposal can be significant. Interpreting the results requires corrections for water density and meter characteristics and it is not possible to carry out repeatability or hysteresis checks on the weighing system using this method.
Applying test weights to weighing vessels can be difficult and dangerous. Bringing suitable test weights to site and then applying them to the vessel is an onerous task, especially if the vessels are on the top floor of the plant with limited access. Health and safety requirements and safe working procedures often prevent this method being used. Also in many applications, no facility for applying the weights has been included in the design.
Note: Other methods such as millivolt injection or electronic calibration are inherently unreliable. There are certain companies promoting the “Electronic Calibration” method with claims of traceability to UKAS national standards. The calibration certificates issued by them only provide the traceability of the test equipment used, not the system under test.