SUPPLEMENT CALIBRATION
HOW OFTEN SHOULD A thermometer be calibrated?
How often should a thermometer be calibrated to ensure it remains as accurate as possible? Does it depend on the application? Or should the calibration be carried out at set times? David Southworth, sales & marketing at Isothermal Technology, comments
T
here are many answers to the question: How often should a
thermometer be calibrated? Google it and the answers will range from
every year, but on one occasion the calibration laboratory calls to say that, when recalibrating, the thermometer had shifted by 5˚C. So, there must be
“In some applications there may only be the need to determine the temperature to a few degrees... For others, making a temperature measurement with only a small error might be disastrous - it could, perhaps, compromise product quality, energy savings or even human life”
‘regularly, if not daily’ to ‘annually’ to ‘after being dropped’. Some manufacturers will recommend calibration intervals, however if the thermometer has a calibration certificate from a laboratory accredited to ISO 17025, then it is unlikely to show a recalibration date. This is because the issuing laboratory will not want to imply specific time validity or be seen to ‘guarantee’ the performance over a certain time period. The user will therefore need to determine the re-calibration schedules based on the application and how the thermometer is used. In some applications, there may only be the need to determine the temperature to a few degrees; and even if there was an unexpected result the consequences may be trivial. For others, however, making a temperature measurement with only a small error might be disastrous – it could, perhaps, compromise product quality, energy savings or even human life. Many people will determine an annual calibration period – and use an accredited laboratory to ensure ‘best practise’.
A DILEMMA Take Joseph, for example. As an employee in the food sector, he uses a thermometer to comply with the Food Safety (Temperature Control) Regulations 1995, and adjusts and keeps a daily log of many large refrigerators to ensure the food is stored at or below 8˚C. He has the thermometer calibrated
S10 MARCH 2016 | INSTRUMENTATION: SUPPLEMENT
some damage to the thermometer or fault with its display. According to Joseph’s log, the food
had been stored at 5˚C, but with this shift it has actually been at 10˚C. This means an offence has been committed – the food has been kept at a temperature which could cause a risk to health, and his company’s future. But when did the problem start? The day before the thermometer was sent away? Six months ago? A year ago when it came back from calibration? This dilemma could have been easily
avoided by checking it regularly in a flask of melting ice, by having a second thermometer and doing cross checks, or investing in simple temperature calibration equipment. An annual
The Venus temperature calibrator from Isotech
VIBRATION CALIBRATOR OFFERS LAB GRADE ACCURACY
New from PCB Piezotronics is The Modal Shop’s (TMS) new 9110D Portable Vibration Calibrator, which is said to offer laboratory grade accuracy and documentation in the form of a field tester. This rugged, lightweight, device is capable of validating accelerometers, velocity sensors, proximity probes and 4-20mA loop vibration sensors, and creates ISO 17025 compliant calibration certificates in Microsoft Excel. Features of the calibrator include closed-loop control, whereby speed remains steady as amplitude changes for confirmation of alert and alarm trips at machine running speed, on-board ICP power, and bias fault indication and real-time sensitivity display to provide instant pass/fail indication. In addition, amplitude display is in acceleration, velocity and displacement (in metric and imperial units), with peak, RMS or peak-to-peak scaling options. It is also capable of storing data for 500 sensors and exports via a supplied USB flash memory drive. As well as satisfying insurance requirements, the TMS 9110D is said to be the ideal tool for troubleshooting vibration protection systems, reducing false trips and confirming alarm thresholds.
PCB Piezotronics
www.pcbpiezotronics.co.uk calibration was not sufficient in itself.
PORTABLE CALIBRATORS Sensors at high temperatures and those regularly being cycled over a wide range are particularly prone to drift and will need to be checked at more than one point. To help, Isotech produces portable calibrators covering temperature ranges from -100˚C to 1200˚C, along with high accuracy thermometers and instruments.
Isothermal Technology T: 01704 543830
www.isotech.co.uk
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