Hand held thermometers

There are many types of hand held digital thermometers used within many sectors of industry from pharmaceutical and aerospace through to warehousing and food production. The thermometers themselves vary from simple on/off version with display hold facilities through to instruments with advanced measurement, differential displays and data logging functions across a range of sensor types. All of these different types and styles have a couple of things in common. These are the central processing circuitry, which could be either electronic conversion or micro-processor based, and could include a l.e.d. or l.c.d. displays and a temperature sensor. The sensor could be internal to the thermometer or an external probe and will normally fit into one of the 3 main categories of temperature sensors - RTD (Resistance Thermometry Device such as PT100), Thermocouple ( of the many different letter often represented by a distinguishing letter - Type J, K, T etc.) or Thermistor.

Probes generally fit into the following categories:-

Did you know?

• The Food Safety (Temperature Control) Regulations 1995 ("Regulations") require potentially dangerous foods to be held at or below 8ºC or above 63ºC.


• The Digitron 2100 series, an evolutionary advance on the 2000 range, when used in conjunction with thermistor and thermocouple probes provide measurement accuracies which are well within those specified in the Food Temperature control Regulations (1995).

Did you know?

• P.R.T.’s in industrial applications are rarely used above 660 °C. At temperatures above 660 °C it becomes increasingly difficult to prevent the platinum from becoming contaminated by impurities from the metal sheath of the thermometer.


• Thermocouple cables are colour coded to type according to IEC/CEI 584.

PRT, Thermocouple or Thermistor

A PRT Probe (Platinum Resistance Thermometer) consists of a bulb, which contains a film or coil of platinum cable. The resistance of this film / coil increases in a linear pattern as the temperature increases. The initial resistance at 0°C, and linear scale is defined by the rating of the PRT (PT50, PT100, PT150, PT500, PT1000)

The tolerance and temperature to electrical resistance relationship is specified by the international standards.

The most common devices used in industry have a nominal resistance of 100 ohms at 0 °C, and are called Pt100 sensors ('Pt' is the symbol for platinum). The sensitivity of standard Pt100 sensors are normally either a nominal 0.385 ohm/°C or 0.392 ohm/°C. This difference is due to anomalies in the European and American standards.

Commercial platinum grades which exhibit a change of resistance of 0.385 ohms/°C are produced according to the European Fundamental Interval. This is defined in BS EN 60751:1996 (taken from IEC 60751:1995). The American Fundamental Interval is 0.392 ohms/°C, and is based on using a purer grade of platinum than the European standard.

Thermocouple Probes are widely used in industry as they are cheap, interchangeable and can measure a wide temperature range. Thermocouples are created by joining two dissimilar metals. The two metals give a variable electric potential difference relative to the temperature difference between two connections. Due to this fact thermocouples do not measure an absolute temperature, but the temperature difference between a ‘hot junction’ and a ‘cold junction’. In hand held thermometers the reference cold junction is built into the hand held unit and taken into account to display the temperature found at the ‘hot junction’ (tip) of the probe. A limitation of thermocouples is accuracy, as whilst Digitron are able to offer a combined system accuracy of ±0.2°C across a limited range, system errors of less than one degree Celsius (°C) can be difficult to achieve

Thermistors are thermally sensitive resistors, where the resistance alters with changes in temperature. Whilst similar to a PRT, thermistors are non linear and will have a temperature vs. resistance curve, according to type. With a negative (NTC) resistance/temperature coefficient the resistance will rise as the temperature decreases whilst the opposite is true for a thermistor with a positive (PTC) resistance/temperature coefficient. A typical ntc thermistor is made using semiconductor metal oxide materials. (Semiconductors have resistance properties midway between those of conductors and insulators.)

Calibration of Hand-held Thermometers

Hand held Thermometers can be calibrated, as a system with one or several temperature probes, between -50 & +255°C, in our UKAS laboratory, which is regularly audited by UKAS. We can offer a wider temperature range, signal injection calibration using equipment, which is certified to UKAS or NPL (National Physical Laboratory) standards.

Hand-held Thermometer Manufacturers

Charnwood Instruments have expertise in the supply, service and calibration of most manufacturers hand held thermometers and work in particular partnership with Digitron, Sifam. Elektron and Testo to provide the correct solution for your temperaure monitoring requirements.

Call 01530 510615 for more information

We are happy to assist you selecting the instrument you require and have many other products available not listed here. For further help email us.

We accept card orders by phone

 

We offer UKAS calibration on these instruments