Fiber Optic Temperature Sensor – Raytek Marathon FA Series


  • High accuracy ± 0.3% of temperature
  • Focus distances down to 100mm (4 in)
  • Fiber optic assembly withstands up to 315°C (600°F); NEMA-4 rated
  • High optical resolution to 100:1
  • 0-20/4-20 mA analog output
  • RS-485 serial output; networkable in any combination of 32 Marathon sensors
  • Advanced signal processing: Peak Hold and Average
  • Background radiation compensation
  • Internal LED display and Marathon user interface
  • Two-way digital communications
  • Programmable relay output: temperature setpoint and “failsafe”
  • Field Calibration Software included

The Marathon FA Fiber Optic Temperature Sensor consists of a rugged fiber optic cable plus optical head assembly connected to an electronics housing containing the detector, processing electronics, internal user interface/LED display, and termination connections for field wiring. These infrared sensors maintain targets in highly confined installations in harsh industrial environments, otherwise inaccessible by non-fiber optic thermometers. The assembly accommodates a small bend radius for threading through tight spaces.

Marathon FA thermometers maintain high accuracy over the ambient operating temperature range from 0º to 60ºC (32º to 140ºF). The fixed-focus optical head consists of a small stainless steel cylindrical housing and lens assembly. The optical head accommodates an air-purge accessory to prevent lens contamination and the fiber optic cable is protected by metal armor. The Marathon FA1G sensor, specifically designed for measuring bulk glass temperature from 750º to 1675ºC (1382º to 3047ºF), permits measurements in melter, refiner, regenerator, and forehearth temperatures.

The Marathon FA Fiber Optic Temperature Sensors include Raytek DataTemp Multidrop software to enable easy and consistent installation, configuration and data capture across the following applications:

  • steel and metals processing
  • glass processing
  • semiconductor manufacturing processing


Environmental Rating IP65 (IEC529) / NEMA-4
Ambient Temperature
Optical head 0 to 315°C (32 to 600°F)
Fiber cable 0 to 200°C (32 to 392°F)
optional up to 315°C (600°F)
Electronics housing 0 to 50°C (32 to 122°F)
with cooling platform up to 150°C (302°F)
Storage Temperature
Electronics housing -20 to 70°C (-4 to 158°F)
Relative Humidity 10 to 95%, non-condensing
Electronics housing IEC 68-2-27
Electronics housing IEC 68-2-6
Optical head 100 g (3.5 oz)
Electronics housing 710 g (25 oz)
Fiber Cable Protection rated to 200°C (392°F), stainless steel armour, Viton coated, IP65 / NEMA-4, provision for conduit to protect fiber cable
Outputs 0/4-20 mA; RS485, 2-wire or 4-wire, networkable to 32 sensors. Relay, 48 V, 300 mA, response time < 2 ms
Power Supply 24 VDC ± 20%, 500 mA


Raytek Marathon FA Series Fiber Optic Temperature Sensor-DpstarGroup