Gallium arsenide based fiber optic temperature signal conditioners

FOTEMPTrafo, Fiber optic temperature monitoring system

The fiber optic thermometer FOTEMPTrafo is an 8-channel thermometer, which is ideal for temperature monitoring of hot spots in transformers.

This multi-channel device together with the TSTrafo temperature probe enable accurate and precise measurements of Trafo windings. By direct installation of the sensors in the windings real, current and quick monitoring is possible.

Through the use of gallium arsenide (GaAs) no recalibration is necessary throughout the product life time. The fiber optic thermometer FOTEMPTrafo is available with 1-8 measurement channels. The compact unit size and the height-adjustable DIN-rail-clip provides an easy installation in the cabinet. A wide selection of interfaces makes communication even easier. The choices are: RS-232, RS-485, USB, Relay, Analog output, WLAN or SD card that ensure an optimal connection. A fast measurement speed of 250ms* per channel allow the direct detection of overloads.

The outer jacket of the fiber optic temperature sensors is made out of teflon, at the sensor tip a GaAscrystal (gallium arsenide) is attached. The probe sensor is completely non-conductive. Optocon’s fiber optic sensors offer complete immunity to RF and microwave radiation with high temperature operating capability, intrinsic safety, and non-invasive use. The probes are also designed to withstand harsh and corrosive environments.

Starting at a light wave length of 850nm GaAs becomes optical translucent. Since the position of the band gap is temperature dependent, it shifts about 0.4nm/Kelvin. The measurement device contains a light source and a device for the spectral detection of the band gap. This guaranties fast, repeatable and reproducible measurements.

Via the analog outputs and thanks to its accompanying software “FOTEMP Assistant”, measurement results can be easily controlled and monitored.

Key Features

  • Measuring range: –200°C to +200°C
  • Standard deviation*: +/–0.2°C
  • Status LED
  • Robust & durable case
  • RS-232, RS-485, USB, Relay, Analog output, WLAN or SD card selectable
  • Choice between 0-10V or 4-20mA analog output
  • Height-adjustable DIN-Rail-Clip


  • Monitoring of "Hot-Spot" inside high voltage transformers, power factor correction capacitors and alternators
  • Temperature measurement on high voltage distribution power lines such as for electric trains
  • Temperature measurement in gas insolated power breakers, in power factor adjustment capacitors

Technical Specifications

Number of channels 1-8
Power supply 24VDC
Measuring range -200°C to +200°C
Standard deviation* +/-0,2°C
Resolution 0,1°C
Measuring time/Channel* 250ms
Analog output 0-10V or 4-20mA
Interfaces RS-232 / RS-485 / USB / Relay / Analog / WLAN / SD card
Data logging Log sequenz via software
Display none
Connector type ST
Form factor IP50
Storage temperature -20°C to +70°C
Operating temperature -20°C to +60°C
Dimensions 240 x 180 x 75 mm
Material Aluminium casting in RAL 9003
Software e.g. FOTEMP Assistant 2 or ASCII-Protocol-Description
Date export Via interface
Warranty 2 years
Probes All fiber optic temperature probes from Optocon AG can be connected.
  *Further information can be found on the data sheet (PDF).