What is fibre optics?

Fibre optics are essentially light pipes. The group of sensors known as fibre optic thermometers generally refer to those devices measuring higher temperatures wherein blackbody radiation physics are utilised. Lower temperature targets, say from -100°C to 400°C can be measured by activating various sensing materials such as phosphors, semiconductors or liquid crystals with fibre optic links offering the environmental and remoteness advantages.

Advantages

Whether used for communications or infrared temperature measurement, fibre optics offer some inherent advantages for measurements in industrial and/or harsh environments:

• Unaffected by electromagnetic interference (EMI) from large motors, transformers, welders and the like
  
  
• Unaffected by radio frequency interference (RFI) from wireless communications and lightning activity
  
  
• Can be positioned in hard-to-reach or view places
  
  
• Can be focused to measure small or precise locations
  
  
• Does not or will not carry electrical current (ideal for explosive hazard locations)
  
  
• fibre cables can be run in existing conduit, cable trays or be strapped onto beams, pipes or conduit (easily installed for expansions or retrofits)
  
  
• Certain cables can handle ambient temperatures to over 300°C--higher with air or water purging
  
  

Applications

Fibre optic thermometers have proven invaluable in measuring temperatures in basic metals and glass productions as well as in the initial hot forming processes for such materials. Boiler burner flames and tube temperatures as well as critical turbine areas are typical applications in power generation operations. Rolling lines in steel and other fabricated metal plants also pose harsh conditions which are well handled by fibre optics.

Typical applications include furnaces of all sorts, sintering operations, ovens and kilns. Automated welding, brazing and annealing equipment often generate large electrical fields which can disturb conventional sensors.

High temperature processing operations in cement, refractory and chemical industries often use fibre optic temperature sensing. At somewhat lesser temperatures, plastics processing, paper making and food processing operations are making more use of the technology. fibre optics are also used in fusion, sputtering, and crystal growth processes in the semiconductor industry.

Beyond direct radiant energy collection or two-color methods, fibre optic glasses can be doped to serve directly as radiation emitters at hot spots so that the fibre optics serve as both the sensor and the media. Westinghouse has developed such an approach for distributed temperature monitoring in nuclear reactors. A similar approach can be used for fire detection around turbines or jet engines. Internal "hot spot" reflecting circuitry has been incorporated to determine the location of the hot area.

An activated temperature measuring system involves a sensing head containing a luminescing phosphor attached at the tip of an optical fibre (Figure 1). A pulsed light source from the instrument package excites the phosphor to luminescence and the decay rate of the luminescence is dependent on the temperature. These methods work well for non-glowing, but hot surfaces below about 400°C

Monitoring Systems

The DP1511, DP1521 and DP1531 non-contact infrared thermal monitoring systems represent a unique technological approach for monitoring and controlling process temperatures. These units combine fibre optics or line-of-sight optics with advanced electronic technology into a system that continuously monitors infrared radiation (a function of temperature) in real time and without physically contacting the target material. The result is a highly reliable system offering outstanding accuracy and repeatability with high response speed.

Also...

The FOB100 Series comprises high-accuracy, multipurpose fibre optic thermometers with 1, 2, or 4 channels. They use an original algorithm to analyse incoming signals, measuring the temperature on each channel.

High Speed Temperature Detectors

The OS1532 detector is designed to be used with the DP1531 high speed monitor. It is offered in a variety of field of view patterns and temperature ranges, and has the ability for backlighting. It is used in applications requiring exceptionally fast response times (down to 0.3 msec) which are unattainable by conventional temperature measurement methods.

Also...

OMEGA's CE marked low cost OS1590 Series infrared fibre optic thermometer / transmitter system measures temperature ranges up to 4500°F and provides dual analog outputs (4-20 mA, 0-5 VDC, 0-10 VDC, 1 mV / Degree, J & K T/C) electrically isolated from the DC power supply input. The main electronics is in a NEMA 4 rated Aluminum housing with a local backlit LCD, built-in Relay, and a 4 position programmable keypad.

2 Color Ration fibre Optic

The OMEGA iR2™ Series is the state-of-the-art instrument for difficult and demanding high temperature (300°C-3000°C) applications. It is ideally suited for measurement and control applications involving metals, glass, semiconductors and more. The iR2 is extremely fast and accurate with a response time of 10 msec and accuracy of 0.2% of full scale.

Portable Fibre Optic Handheld

The HHTFO-101 offers impressive versatility. Battery operated for maximum user freedom, this single-channel instrument allows you to freely move from one area to another to measure temperatures at various critical sensing points. The HHTFO-101 is a valuable monitoring tool for a wide range of applications in energy, industrial and research activities, such as hot spot monitoring inside power transformers during manufacturing and heat runs. It can also be used in various high voltage applications and MW/RF heating applications.