Fibre Optic Temperature Measurement: Pyrosales & Hitele

06 February, 2009

Fibre optic technology measures the signal produced by the scattering of light along an optical fibre. The Hitele Fibre Optic Systems supplied by Pyrosales can help to maintain process control and ensure safety.

The use of optical fibres as a temperature sensor is a comparatively new technology. Fibre optic technology uses a laser light source to inject a light pulse along as optical fibre. The pulse mostly travels to the end of the fibre and disappears, but a small proportion of the light is reflected back along the fibre. This backscattered signal is collected an analysed within an opto-electronics unit to provide temperature information about the fibre.

The essence of the output is a profile of the temperature along the whole length of the fibre, for lengths up to 30 km, and beyond. The whole length of the fibre can be divided into zones which can be as little as 1 metre long with different temperature readings in each zone. The system can be set up to give a temperature profile of the fibre length or to give alarms if the preset temperature limits are exceeded.

The Hitele fibre optic systems supplied by Pyrosales have a temperature accuracy of +/- 1ºC and can operate between -200ºC and 500ºC. Fibre optic systems are also intrinsically safe and allow for remote operation.

Summary of Features:

  • Comprehensive model range from specialised fire alarm units to 30km range model.
  • Complete Turnkey Package from design to installation and training.
  • Temperature Accuracy of +/- 1ºC.
  • -200 to 500ºC Operation.
  • Single Ended Operation.
  • Not Affected by Electro-Magnetic Interference (EMI).
  • Intrinsically Safe.
  • Remote Operation.


The applications of fibre optic technology are numerous and ever-increasing. Some of the main applications are listed below.

Power Cables
Fibre optic systems can monitor temperature and loading on buried or concealed cables providing invaluable performance data.

Fire Detection
Optical fibre temperature measurement systems are extremely reliable and effective as fire detection systems in arduous or hazardous conditions such as road and rail tunnels or coal mining applications. The sensor cable is unaffected by pollutants or electromagnetic interference and is inherently safe.

Hot Spot Monitoring
Detection of hot spots on furnace walls or insulated bodies can be used to provide essential information for process control and safety. The fibre optic system can cover the whole of the hot (or cold) body and the information used to predict deterioration of insulation at the most vulnerable locations.

Leak Detection
Fibre optic systems can monitor continuously for downward temperature changes, which can be detected and used to activate an alarm.

Geothermal Wells & Down Hole Applications
Monitoring water flow and temperature gradients within geothermal wells gives important information for lifetime prediction and operation control. The difficulty of placing sensors into deep holes with narrow bores can be overcome because of the single end connection required by the Hitele fibre optic units. Outside of the specifics of geothermal wells there are many other down hole applications, including effluent treatment and fossil fuel exploration.

Designers and materials scientists involved with large concrete bodies such as dams can derive benefit from knowing the temperature of their structures. Optical fibre sensing can be used to monitor the curing temperature of the concrete and can later provide a continuous monitor for leak detection.

Process Monitoring
In chemical and pharmaceutical processing, temperature distribution information can be used to give incremental improvements. Additionally, the use of low power laser light is intrinsically safe, which lends itself to hazardous area use.