Calibration: Scales, Thermometers


Internal Calibration

The calibration process is to ensure all equipment used to inspect, measure or test the food process of product is reading accurately at the time of use.

 

To ensure compliance towards:

  • FSANZ Code, Standard 3.2.2 Food Safety Practices: [22 Temperature measuring devices (b) can accurately measure the temperature of potentially hazardous food to +/- 1ºC]
  • National Trade Measurement Regulations 2009 [scales]

 

Calibrated measuring, test and inspection equipment should be kept safe and hygienic to protect them from damage and unauthorised adjustment.

 

Critical Criteria of Measuring Devices

Scales 0.1% of the calibration weight
Standard Mass Weights 0.1% of the mass of the calibrated standard weight
Thermometers – Probes, Infrareds ±1°C
Temperature Gauges ±1°C

 

Frequency

The frequency of internal calibrations shall depend on how often the equipment is in use and the level of reliability of such equipment for your finished product.

 

For example, if product is sold on weight, consider conducting calibration checks daily, weekly or monthly, depending on volume output of finished product.  Otherwise quarterly calibration checks can suffice.  If measuring devices purchased are of questionable integrity and quality, consider an increase of calibration checks.

 

Minimum requirement is every 12 months, but do consider that 12 months is a long time to wait between checks.

 

Record Keeping

For every calibration conducted, it must be recorded, as evidence of your verification.  Record keeping may be on separate Internal Calibration record sheets, or if calibrating often, may be included in your existing production log or maintenance log.  There are examples at the end of this document of stand-alone calibration record sheets for Scales, Thermometers, Chillers and Freezers.

 

New Equipment

  • All new measuring devices should be supplied with a calibration certificate
  • Should no calibration certificate be supplied, internal calibration of the new device must be performed and documented

Probe Thermometer

For thermometer internal calibration checks, you may conduct against a calibrated reference thermometer for ambient, chilled, or freezing temperature points, or the ice slurry and boiling point methods of below.

 

For thermometers used to take the temperatures of chilled/frozen items: Zero Check: Ice Point

  • Select one of the probe thermometers as the “control thermometer”
  • Add ice made from tap water into an insulated vessel
  • Slowly add enough tap water to make a slurry and mix (approximately 70% ice to 30% water)
  • Allow to sit for about 30-60 seconds; this will chill the water to 0°C
  • Place control thermometer into the slurry ensuring the thermometer probe is immersed to a depth of at least 60mm
  • Allow the readings to stabilise before recording
  • Notes: Ice floats, so be mindful if your probe is at the bottom immersed only in water: it needs to be immersed in the ice slurry. If possible, crush ice or use small ice cubes to allow for an effective mixture of water and ice

 

For thermometers used to take the temperature of hot items: 100°C Check: Boiling Point

  • Use the same controlled thermometer from the above ice point calibration
  • Place the control thermometer into boiling water, ensuring the thermometer probe is immersed to a depth of at least 60mm. Use tongs to hold the thermometer to prevent burns to fingers
  • Allow the readings to stabilise before recording

 

For thermometers used to take the temperatures of ambient items:

  • Select a thermometer that has been calibrated as above (ice slurry/boiling point)
  • Place the controlled thermometer by the second thermometer
  • Allow the readings to stabilise before recording

 

Infrared Thermometer

The most reliable process would be to purchase an Infrared Comparator Cup.  We provided you a link to ECE Fast, but you may purchase one from any reliable measurement and control business.  The Infrared Comparator Cup provides a stable black body temperature of checking infrared hand-held thermometers against a known reference thermometer.

 

Alternative methods:

  • Point laser gun (infrared) as close as possible to the ice check point (ice slurry)
  • Alternatively, place the controlled thermometer near the spot the laser gun shall be pointed at and compare results
  • Allow the readings to stabilise before recording

Chillers, Freezers, Temperature-Controlled Vehicles

  • Place the controlled thermometer within the equipment
  • Allow the readings to stabilise before recording
  • Note: If no thermostat, calibrate against the thermometer dial within the equipment

 

Scales

  • Using a calibrated mass weight, place on the scale and check that the scale reading is correct
  • Ensure mass weight is placed on all five points of the scale:
  • Record result

 

Corrective Actions for all internal calibrations

  • Scales: Press “tare” to balance scales; check that the legs of the equipment are balanced on the table; ensure no build up (food, etc.) on the scales
  • If out of variance or damaged, stop using equipment and replace with backup equipment
  • If applicable, replace batteries
  • Immediately report to the QA team
  • Ensure damaged equipment is clearly labelled and removed from production
  • Contact equipment supplier to check/amend equipment
  • Report issues in the Corrective Action section on your dedicated record sheet
  • Ensure no products will be released from the facility out of specification
  • Investigate occurrence of non-conformance and if required, follow your Non-Conforming Product or Equipment policy

 

Emergency Procedures

Chillers: ·         If a fridge is out of calibration or not functioning, remove all stock from the “damaged” equipment and place neatly and together in the functioning equipment

·         Check stock if outside of critical limits.  If time unknown outside of critical limits, discard food items

·         To be conducted with care and within a timely manner.  Ensure raw, work in progress, and finished product remain segregated

 

Freezers: ·         If a freezer is out of calibration or not functioning, all stock must be moved to the most empty chiller or another freezer.  Ensure raw, work in progress, and finished product remain segregated.  Use thaw day dotting if required

·         If freezer is fixed within two hours, check all stock for integrity before returning to freezer

·         If items are no longer hard frozen of if over two hours, stock must remain in chillers and be utilised as soon as possible

 

Thermometer: ·         Change batteries or replace thermometer with a new one

 

Example Calibration Schedule

Please refer to QA Calendar when calibration of equipment is scheduled.

Equipment Variance Frequency How Responsibility Back Up Equipment
Scales ±1g Monthly Mass weights QA team Use another scale that has passed internal calibration testing
Thermometers (probe, infrared) ±1°C Monthly Reference thermometer or Ice-slurry, boiling point QA team Spare thermometer
Chillers, Freezers ±1°C Bi-annually Reference or controlled thermometer QA team Follow Emergency Procedures (above)
Transport Vehicle
(chiller/freezer)
±1°C Quarterly Reference or controlled thermometer QA team Contracted Van

 

 

External Calibration

Licenced Verifiers

  • Only licenced verifiers approved by the National Measurement Institute shall be used to conduct calibrations
  • Note: Current licences can be checked on http://www.measurement.gov.au

 

External Calibrations

External calibrations may be conducted under the following circumstances:

  • NATA-certified Reference Thermometer Annually
  • Standard Mass Weights (varied) * Every two (2) years (every odd i.e. 2013)
  • Purchase of new measuring equipment (if a calibration certificate is not supplied)
  • Ongoing raised corrective actions or, if no raised corrective actions, minimum five years of each measuring equipment from last verified calibrated certification, where applicable/required
  • Measuring equipment: Handheld thermometers, thermostats, oven temperature gauge, scales, standard weights, etc.
  • External calibration service reports are retained

 

Corrective Actions for all external calibrations

If the thermometers, thermostats, gauges or scales are found to be out of calibration, it is recorded and immediately repaired by the contractor.  Also:

  • If out of variance, cease use immediately
  • Replace with backup equipment, whilst equipment is checked/amended by Calibrator or Equipment Supplier
  • Report issues in the Corrective Action section on your dedicated record sheet
  • Ensure no products will be released from the facility out of specification

 

Example Calibration Schedule

Please refer to QA Calendar when calibration of equipment is scheduled.

Equipment Variance Frequency Responsibility Back Up Equipment
Standard Mass Weights ±1g NATA – Annually

Reg. 13* – Every 2 Years

Stainless Steel – Every 3 Years

Contractor
Reference Thermometer ±1°C Annually Contractor Calibrated Thermometer

* Reg 13 = Regulation 13 Certificate

 

Example of Record Keeping Templates

 

 

Download this article:  Calibration ed 01 – 02-06-19

 

 

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