How to select the correct Temperature Sensor

Overview

A Temperature Sensor is used to obtain an industry standard output of the temperature level of the measured parameter. Cynergy3 produce both wired and wireless temperature sensors which utilise thermocouple or RTD (Resistance Temperature Detectors) sensor elements.

The temperature sensors are typically 6mm OD sensors with lengths varying from 150mm to 600mm, although other sizes are available from Cynergy3. The sensor comprises the probe section which is immersed in the fluid to be measures and the head part which contains either the 4-20mA output wired transmitter or the wireless transmitter and battery.

 

Uses

The uses of temperature sensors are many and varied but for our range of sensors all typically involve the measurement of a liquid or gas within a tank or pipework. The choice of RTD or thermocouple will depend on the temperature range and accuracy required and the choice between wired and wireless will depend on the accessibility of the pipework or tank, the output required and cost of installation against cost of purchase. RTDs are used where repeatability and accuracy are important and the temperature measured will not exceed 850 °C. RTDs are also more susceptible to vibration. Thermocouples can be used up to around 1250 °C and are typically more durable than RTDs.

 

Function

Cynergy3 wired temperature sensors utilise an in-head transmitter which converts the RTD or thermocouple signal into a 4-20mA output signal which is linear to the temperature range being measured. The in-head transmitter is a 2-wire device, a 24Vdc nominal voltage is connected to the positive terminal and the negative terminal is connected to the input terminal of the measuring equipment. The in-head transmitter controls the current flowing in the loop from between 4mA and 20mA. If a range was 0-500 °C then the unit would supply 4mA at 0 °C, 20mA at 500 °C and 12mA at 250 °C.

Our wireless temperature sensors convert the measured temperature into a 16 bit digital value and transmit this value to the wireless receiver at the configured update rate, typically every 10s to every minute. The receiver than converts this signal to either a 4-20mA or 1-5V analogue output or stores the value as a Modbus register to be read by the measuring system connected.

 

Considerations

Cynergy3 temperature sensors are highly configurable to the users’ needs. When selecting a temperature sensor for a given measurement application, it is vital the user has clear understanding of the temperature sensing application and the media that needs to measured. There are many factors that need to be considered, and in some cases, trade-offs will need to be made, to find the optimum temperature sensor configuration.

  • Process media to be measured: gas, liquid, media temperature.
  • Temperature range to be measured.
  • Depth of pipework or tank will determine the length of sensor required.
  • Accuracy of the temperature reading required.
  • Compatibility with the downstream measuring equipment.
  • Wired or Wireless requirement, based on ease of install and cabling considerations.
  • Is there a risk of vibration at the measured location, thermocouples are typically more resilient.

 

Types

All our wired and wireless temperature sensors are supplied with a cable gland and this can have either a 1⁄4” BSP or a 1⁄4” NPT thread. Please specify the correct thread required at the time of order. The length of probe and the type of sensor required must also be specified using the selection criteria above.

For non-standard or OEM requirements please contact Sales using [email protected].