Temperature Sensor

Temperature is the most commonly measured parameter in industry, with almost all industrial processes measuring or controlling temperature as part of their requirement.

To compliment our range of equipment we offer a range of temperature sensors specifically designed for measuring the temperature of liquids used for process control, effluent treatment and water treatment.

All of our temperature sensors are RTD's and we use a 3 wire PRT (platinum resistance thermometer) devices using either a PT100 or a PT1000 as specified at the point of ordering.

RTD's (Resistance Temperature Detector)

The temperature sensor models that we supply are all RTD's or Resistance Temperature Detectors. The electrical resistance of these devices changes as the temperature increases.

PRT (Platinum Resistance Thermometers)

The material of choice for use in our RTD's is Platinum - which makes all of our temperature sensor range Platinum Resistance Temperature Thermometers.

We use platinum as it it's the noble metal with the most stable and repeatable relationship between temperature and resistance. As standard we supply our temperature sensor ranges with a PT100 temperature sensor. Alternatively we can fit a PT1000 temperature sensor if specified.

Our temperature sensors are designed primarily for measuring the temperature in liquids used for process control, water treatment and effluent treatment. Using a PRT for these applications means that we can measure the temperature very accurately. The PRT's aren't suitable for measuring temperatures in excess of 300°C - and we rate all of our temperature sensors to a maximum temperature of 250°C.

PRT Theory

We choose to use Platinum Resistance Thermometers as standard because of their excellent linear relationship between temperature and resistance. The below charts shows the resistance and temperature relationship of a standard PT100 PRT found in one of our temperature sensor.

As the temperature increases the resistance also increases. By connecting the PRT100 to a compatible temperature controller or as an input on another device such as a (conductivity controller or pH controller that uses automatic temperature compensation) a small voltage is passed through the PRT and by Ohms law we can deduce the temperature at the tip of the sensor precisely. 

3-Wire Temperature Sensors

PRT Sensors do have some limitations. They aren't recommended for temperatures over 300°C and aren't suitable for temperatures greater than 600°C. As our instrumentation is designed primarily for liquid temperature in process conditions or water and effluent treatment - and not the temperature inside furnaces or ovens, this doesn't greatly affect the equipment that supply.

Another limitation is that the PRT has a changing resistance inline with the temperature. As this resistance change is both linear and very precise - the length of cable can introduce a resistance which can be falsely attributed to a rise in temperature. To overcome this our temperature sensors are a 3 - wire device. The 3rd wire is the same length as the two wires which supply the signal to the instrument that indicates the temperature. As it's the same length and manufactured in the same material - the resistance of the wire is the same as the two wires supplying the signal.

By subtracting the resistance of the 3rd wire from the measured resistance 2 signal wires we can accurately measure the resistance and calculate the temperature precisely.

4 Wire temperature sensors for use when a wire is very long are available. These use a wheatstone bridge arrangement so that the resistances cancel one another out. There is significantly greater complexity (and cost) involved in using this type of arrangement, so when a long cable run for a temperature sensor is required - we suggest using our TT100 4-20mA temperature transmitter in conjunction with a 4-20mA controller instead. This way the cable length can run up to 3000 metres away with no problems.

We offer three main types of temperature sensor which are all 3-wire PRT type temperature sensors and are as follows:-

• TPA-1 range of insertion sensors with a threaded boss welded onto the temperature sensor.
• TPA-2 range of immersion sensors designed for dip mounting or immersion mounting into tanks.
• TPA-3 range of insertion sensors with quick release connector designed for use with a temperature pocket / thermowell using a compression fitting or optional welded boss.

Insertion Temperature Sensors TPA-1

The TPA-1 range of insertion sensors are with 75mm of lagging and a welded boss included on the temperature sensor itself. The boss is normally 1/2" BSP threaded although we can accommodate different sizes if required. This is normally connected directly into a process fitting, temperature pocket or a thermowell.

The TPA-1 series are available with either an ABS head or an aluminium head.

Immersion Temperature Sensors TPA-2

The immersion temperature sensors are supplied with a stem measuring 6mm Ø or 12mm Ø. The stem is normally supplied straight but we can supply our TPA-2 immersion temperature sensors with a 45° or 90° bend if required.

The TPA-2 temperature sensor range is available with either an ABS head or an Aluminium head. These stem can then be immersed into a tank, vessel, or water course to provide continual temperature measurements. The TPA-2-N with an ABS head can be fitted into a temperature pocket or thermowell using a compression fitting. We suggest avoiding this with the TPA-2-A with aluminium head due to the risk of bending the stem.

Chemically Resistant Temperature Sensor

As out temperate sensors are frequently used for measuring the temperature of solutions within process vessels, we offer a range of chemically resistant temperature sensors designed specifically for this purpose. The TPA-2 sensor range are re-engineered to include wetted parts in PVDF and PTFE for greater chemical resistance.

Insertion Sensor with Quick Release Connector TPA-3

The TPA-3 range of temperature sensor are all fitted with a DIN specification connector mounted on to the head, this is designed to aid fitting and removal of the temperature sensor.

The TPA-3 is available with either a threaded boss to allow direct insertion into a  temperature pocket or thermowell either by directly screwing a TPA-3 fitted with a threaded boss into into the thermowell, or by using a compression fitting to secure the TPA-3 into place.