2. Scope and General Principals
This Code of Practice covers weighing and measuring equipment used in the batching and manufacture of cementitious and cement bound materials. It does not apply to equipment used for sample testing or specification conformity testing; such equipment is predominantly required to be calibrated in accordance with UKAS procedures and is, therefore, outside the scope of this document.
Continuous weighers are not covered by this Code as they are by their very nature unique, application specific devices and they require unique on-site specific calibration procedures. The calibration procedure used for such machines shall be documented either as a site procedure or as a specific procedure by the calibrating organisation.
The general principles of accuracy, integrity and recording of results contained in this Code shall apply.
Customers are advised that the accuracy of Calibration is a function of the integrity, training and competence of the person/organisation carrying out the calibration. Calibration also requires the co-operation of the customer to make the weighing equipment available for sufficient time for the work to be carried out and ensure that adequate facilities, assistance and materials are available.
As a general principle, the UKWF recommends that a full calibration should be carried out at least every three months, and that interim checks are carried out as agreed with the customer. It is recommended that equipment that has a high output be calibrated more frequently. In a number of cases, the Certification Body responsible for the assessment of the customers’ quality management system will specify maximum intervals between full calibrations and interim checks. The frequency of calibrations and interim checks shall be agreed in the contractual arrangements between the customer and the calibrating organisation.
The signature of the person carrying out the calibration is the customers safeguard for the integrity and validity of the calibration. It is essential that the person signing the calibration record is the person who has noted the readings/indications of the equipment during the testing phase. The signature of the customer representative receiving the calibration certificate is regarded as an indication that the calibration has been carried out to the customer’s satisfaction. If it should arise that the customer or his representative is not so satisfied they should still sign the certificate but should endorse it, commenting on their dissatisfaction, and the reason.
In cases where the customer does not provide the necessary assistance and facilities to carry out the testing efficiently it must be recognised that the calibration time will be increased.
Many customers are implementing sealing arrangements or other methods of securing the integrity of the calibration parameters between calibrations. The calibrating organisation shall co-operate with the customer in the use of such systems, and in instances where calibration seals are found to be broken at the time of calibration this shall be recorded on the calibration certificate.
QSRMC requirements are that calibration seals incorporate an identification mark and that the calibrating organisation has a document control system for traceability of such seals. Paper seals should destruct when removed. Potentiometer pots controlling coarse tare or span shall be protected by a seal. When primary or secondary calibration of the system can be adjusted via the keyboard of the computer system there shall be a non-resettable event number (event logger) displayed within the calibration screen. Calibrating organisations shall record previous and existing event numbers on the Calibration Certificate.