Application Guide Sensor Tech Ltd

Please have a look through our application guide below that contains all that you need to know about your application and how to maintain it and recognise malfunctions.  Thermometers are very sensitive pieces of equipment but if you follow some of the information in the application guide you will prolong the lifetime of your device.

Some of the information below is hidden from view but if you simply click on the + plus symbol to the left of the text it will expand out for reading.  All our thermometers are of a ISO 9001:2000 standard and we are a registered firm.

Calibration check

It is important to have a means of checking the accuracy of your meter between Calibrations.  The most popular checks are Zero and 100°C.

0.0°C Check

Use crushed ice & water preferably in a vacuum flask.  Firstly pack the flask with crushed ice & then top up with water to give a slushy ice mix.  This is a very accurate, simple and mobile check.

100°C Check.

This is more difficult to achieve.  Many people use a kettle to check the thermometer at boiling point.

Care must be taken to get an accurate result. Some makes of thermometers can be too sensitive and respond to the super heated steam in a seemingly
erratic display of temperature.

  1. Continuous boiling action will help to keep the water agitated. If hot water is allowed to settle a temperature strata begins to form, hot on top and cold on bottom.
  2. Allow for atmospheric pressures. Variations in pressure (both weather and altitude) will cause the boiling point to change. At sea level the error can be +/- 1°C(970 to 1030hp).
  3. Use a Reference thermometer in place of (2) above.

Core temperatures/meat product

This should be measured at the centre of the thickest part of the product.  The probe should penetrate to at least 10 times its diameter away from bone, fat or gristle.  With thin product such as Hamburgers and Pizzas the temperature should be measured by inserting the probe sideways.  Use a suitable diameter probe.

  1. It is not recommended to measure the core temperature by inserting the probe in from the top or side of the product or press lid. This is like trying to find “The Bulls Eye”. It takes an expert on a good day to get it right and leaves no margin for error. The error in this case can be a few degrees C or more and is usually highlighted by differences in the readings between the internal oven probe and hand held thermometers.
  2. The probe should be inserted in from the front or back along the centre axis of the product. The result of this simple change helps to de-skill the procedure while giving more accurate and repeatable readings. In the case of the cooking press this may mean drilling an extra hole in the press.

Comparing, two or more Thermometers.

This method is often used to confirm accuracy. Ideally use an Ice Reference (see 0.0°C above). In practice however this may not be available. For a rough guide tie both probe tips together with an elastic band for good contact.

Between pack

This is a non-destructive method for taking the temperatures of prepared food products. It can also be the most difficult. The probe choice will be determined by the type of product, Vacuum packed meat products (rashers & sausages) are good conductors of temperature helped by their close contact with the packaging. This makes it possible to take temps using small steel probes or Between Pack probes. However when measuring between products that are poor conductors such as bread, gas flushed vacuum formed packs, use low mass Between Pack probes.

Non-contact, infrared Thermometers.

These meters work on the principle that all bodies emit infrared radiation in proportion to their temperature. Using infrared detectors this temperature can be measured; however there are some problems in applying this technology to the everyday operations of the food industry. The accuracy of these measurements will depend on the following.

  1. Emissivity. This relates to the ability of a body to absorb or reflect incident radiation. As a rule black bodies absorb all incident radiation so that all emitting radiations are a result of their own body heat. They have an emissivity factor of 1.0. However shiny surfaces reflect a lot of incident radiation and therefore need special compensation i.e. emissivity factor less than 1.0. This is not an exact science. It is not uncommon to get readings in a fridge that pick up your own body heat reflected from the shiny surfaces.
  2. Ambient temperature compensation. As with all thermocouple thermometers these infrared detectors have internal temperature sensors which compensate for changes in ambient temperatures. They should be allowed to stabilise in the environment where they are being used. Check the manufacturer’s specifications to make sure that they can operate at these ambient temperatures.
  3. The laser dot is not the point of measurement. The surface being measured is described by the base of a cone whose tip is at the sensor and whose diameter varies with the distance between them. This “cone angle” is given as a ratio and is specified by the manufacturer. A 6:1 ratio for example means a distance of 6cm will measure a spot of 1cm.
  4. Take the reading and remove the thermometer. Continuously holding the sensor over a product can cause errors through the heating or cooling effects of incident radiation on the sensor.
  5. Difficult to calibrate
  6. Use discerningly

Cartons and containers

With salad dressing in a plastic containers. Soup/milk in cartons, outer palletised cartons the probe choice will depend on the weight and depth of the cartons.

  1. Use a probe with the lowest thermal mass that the situation will allow. i.e. the thinnest tube, the flattest sensor or a low mass sensor.
  2. Keep the thermometer in the testing area to allow the meter and probe to stabilise. This is important for thermocouple type probes.
  3. It may help to pre-cool a steel probe.