Mark Johnston, from Industrial Automation Asia (IAA), spoke with Mitsuo Shimizu, Assistant Manager, and Yoshinori Sato, Manager, Quality Assurance Department, Hioki Corporation on the top five most asked questions about calibration. Their insightful article follows.
Hioki electrical measuring instruments are comprised of four product groups: automatic test equipment, data recording equipment, electronic measuring instruments, and field measuring instruments. Used extensively across different industries for a range of applications, the company has five calibration and service centers globally. Calibration is an integral part of achieving accurate, repeatable, results. What follows are the five most asked questions about calibration, according to Mitsuo Shimizu and Yoshinori Sato, from the company’s Quality Assurance Department, located in Japan.
Q: How do you determine the calibration points?
First, follow the recommendation of the manufacturer. Then, if necessary, customize the calibration according to the functions, range and measurement level of the user of the equipment under calibration.
Q: How do you determine the calibration period?
First, follow the recommendation of the manufacturer. If the customer has records of calibration data from previous years, analyze the data and adjust the calibration frequency so that the next calibration is conducted within a similar period. For electrical measurement equipment, generally, 1-year calibration periods are the most common.
Q: How do you select the reference and calibration equipment?
The ratio between the accuracy of the reference equipment and that of the equipment under calibration should be at least 4:1.
A customer may choose to calibrate themselves or send their equipment to one of our calibration and service centers. We do not require the customer to return the equipment to Hioki to be calibrated but there are advantages to doing so, namely, we also have the capability to repair and adjust the equipment to ensure it is operating optimally for the customer. This is part of the total after service support we offer our customers. Hioki has five such calibration and service centers globally,
Q: Does all test equipment need to be calibrated?
When differences in measurement capacity and measurement values have an effect on the customer’s work, the test equipment should be calibrated regularly. For example:
- When measuring the earth resistance after installing earthing equipment in a factory and official records are required.
- When measuring the commercial power voltage being supplied to a factory, and the power supply affects quality.
- When the diameter of the cables being manufactured by a factory need to be measured for quality control, and the measured values are compared to standard or allowable ranges.
Test equipment that does not need to be calibrated are those that do not have an effect on the customer’s work despite variations in the measurement capacity or value. For example:
- When measuring the earth resistance after installing earthing equipment, and the customer only needs to check if there are any wiring breaks or disconnects.
- When measuring the commercial power voltage being supplied to a factory, and the customer only needs to check whether or not power is flowing.
- When the length of the cables (which is not an important parameter) being manufactured by a factory are checked to see if it falls within a certain range.
Q: What is the advantage of ISO/IEC17025 calibration?
ISO/IEC17025 is an international calibration standard, and the calibration data indicated on the calibration certificate is officially assured for international traceability. Such a certificate helps to eliminate trade barriers and heighten reliability, making it easier to obtain approval from government authorities or other entities that require similar qualifications.
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