Tipskey
Measurement Equipment Calibration
This article is not about how to calibrate a certain piece of equipment. It is about how to manage calibration.

Measurement equipment gives a number with measurement unit from interaction with work piece. For example if a fastened nut cannot be loosened with 40 Nm torque wrench but can be loosened with a 50 Nm torque wrench, then the torque of the fastened nut is 50 Nm.

Calibration involves comparing the reading of a measurement tool against the standard and adjusting the tool if the reading does not match. For example, if a power supply with built-in voltmeter shows 100 V, but the output measured with a reliable external voltmeter shows 110 V, it is time to calibrate the power supply.

Any other equipment without measuring function does not need calibration.

Using the measurement tool

When using measurement equipment to inspect product, the user is to record the equipment number and its calibration deadline besides the measured result in the inspection report.

Each user is to be given one unit of hand equipment if that hand equipment is frequently needed by more than one user at the same time. The user should delicately handle the measurement equipment so that
a) calibration sticker stays in tact
b) the equipment is free from conditions that may affect accurate reading (e.g. shock, moisture, sudden change of temperature).

Avoiding overdue of calibration deadline

If the equipment owner (production, test or service department) is unable to monitor the calibration deadline, an independent department (e.g. QA, Research, Finance) should involve. The user of the equipment must not reject the pickup for calibration. The independent department is empowered to initiate work or delivery stop when the measurement equipment is due for calibration. The user may suggest to calibrate the equipment earlier during idle period in production schedule if the calibration deadline will fall in in a peak period.

Having a master list of measurement equipment helps in monitoring. The list may be in the sequence of the asset number (a number internally generated and affixed on the equipment) or serial number. Although the serial number format is different for different manufacturer of equipment but it can still be arranged in sequence. Example of list:

Asset#Serial #Measurement EquipmentBrandModelDue dateAlert
       

In spreadsheet, the cell in Alert column is to be formulated with
=IF(TODAY()+10>cell in due date column, "Late", "")
so that it will display the word Late if the delivery is almost due (10 days before) or is already due.

To cut down the work in monitoring, the calibration deadline for all equipment can be standardized to be on only one or two dates.

Sending for calibration

The department owning the measurement equipment engages the calibration vendor. Choose a vendor that
a) is accredited as a calibration lab by local government for the types of equipment it intends to offer service.
b) has a certificate of ISO/IEC 17025.
c) will prompt the user and the monitoring department when the calibration is almost due.
d) will write in the calibration report whether adjustment has been done.
e) offers the fastest delivery.

To avoid idle operation while waiting for the measurement equipment to come back from calibration, two pieces of similar equipment should be available. When one is sent for calibration, another can be used. Another option is to temporarily rent the equipment.

If the calibration fee is higher than the price of new equipment, the company can decide to replace it.

Calibration tag

Calibration record

Measurement equipment, including newly purchased unit, is to be attached with durable and tamper-proof sticker on calibration deadline. Wherever a sticker cannot be affixed on the measurement equipment itself, instead the storage case or the storage place is affixed with the sticker.

The department owning the measurement equipment keeps hardcopy calibration certificates. That department shall scan the certificate into softcopy and send to the independent department that monitors calibration deadline. The filing should be in a sequence that enables quick retrieval. When the new calibration certificate comes in, the old hardcopy can be disposed off. Do not keep old and new copy in the same folder to avoid confusion. The softcopy is kept for a number of years based on company product life time. The softcopy file name may follow this format: number used for sequence + due date + Brand + measurement equipment (e.g. 97230150 due 2011-09-09 Fluke multimeter.pdf).

When the newly purchased measurement equipment is used officially for the first time, keep a scanned copy of the product test report as part of the calibration management record. Official product test report contains the serial number of the measurement equipment used. The first calibration date can be set based on the date of the equipment's first use.

Interval until next calibration

The interval until recalibration for most measurement equipment is one year. The basis (e.g. applicable international or national standard) of setting the interval should be available. The equipment manufacturer and calibration vendor should be able to provide this information.

Review historical calibration to see if a certain model of measurement equipment has not needed adjustment for two consecutive calibration intervals. If yes, then the company may redefine the length of calibration interval for that model. For example, if 2010 and 2011 reports show no adjustment, then the company may ask the calibration vendor to print the report and the sticker to be due in 2014 during the calibration in 2012.

Example of equipment that needs calibration and its calibration interval:

EquipmentYear
Anemometer3
Cathode ray oscilloscope, scopemeter2
AC/DC clamp meter1
Crimping tool, pressing tool1
Distortion factor measurement equipment2
Hand pallet truck with embedded weighing scale2
Temperature logger1
Thermometer, thermocouple1
Torque wrench1
Voltmeter, ammeter, megohmmeter, multimeter2

Re-calibration may be triggered by the user even before the calibration due date if the equipment has experienced fault conditions or suddenly the reading appears questionable. Delivery stop or product recall may take place in this case. If the reading gives uncertainty for two times or more before calibration due date, see if the environment has changed drastically (temperature etc). If no, it is recommended for the company to change to another brand of measurement equipment or to redefine calibration interval.

For measurement equipment that cannot be adjusted (e.g. ruler, vernier caliper, glass thermometer), there should be justifiable evidence that the product quality is not affected if the company decides to use it as it is. It is still recommended to get a one-time measurement verification certificate from accredited lab. If it is a measuring tape, internal verification at defined period should be done because the tape may get elongated with frequent usage.

Measurement equipment not owned by the company

If a process that uses measurement equipment is outsourced, ensure that the subcontractor's equipment is calibrated.

For customer-owned measurement equipment, it is good to check whether the equipment has calibration certificate. if the company has TS 16949 management system, it is compulsory to stop using the customer-owned equipment if its calibration status is unknown.

Others

When purchasing new measurement equipment, the manufacturer of the equipment is to provide a record that the equipment has been calibrated before releasing.

If a piece of equipment is partially faulty in a way that it can still measure but cannot be calibrated, and the company wants to use it as a "working tool" in which only an estimate value is needed and no value will be recorded, it must be labeled clearly to prohibit the use as official measurement equipment. There shall still be record of checking the value annually against calibrated equipment and if the deviation is too big, the equipment is to be disposed off.

It is good to internally compare the reading against a similar equipment that has been externally calibrated before
a) using a new equipment.
b) taking a critical measurement.
Posted: 2011-02-06; updated: 2015-01-20 by Ong Seng Aun.
Home       About       Privacy       XHTML 1.0 Strict