Fiso FOT-L

Temperature Sensor for Harsh Conditions

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Key Features
  • Temperature measurement to 300°C
  • Intrinsically safe
  • High accuracy
  • Fibre optic
  • For harsh environments
  • Immune to EMI/RFI
  • No interference due to cable bending
Buy Online

We currently don't have any FOT-L parts to order online. Please call +44(0)118 9769000 for further assistance

Ordering Information

Product Code Description Notes
FOT-L-SD-C1-F1-M2-R1-ST Fibre optic temperature sensor; range of -40°C to 300°C; 30mm standard tip; PTFE cable with 1mm OD; 50µm fibre; 2 meters; Precision of ±1°C; ST connector standard
FOT-L-BA-C1-F1-M2-R1-ST Fibre optic temperature sensor; range of -40°C to 250°C; 20mm bare tip; PTFE cable with 1mm OD; 50µm fibre; 2 meters; Precision of ±1°C; ST connector standard
FSP-079 Calibration certificate for either of above option

Additionally, cables and measurement range/accuracy may be customised. Standard options are listed below, but other customisations are available on request

Cable options

Cable code Description
C1 PTFE cable with 1mm OD
C2 PTFE cable with 1.7mm OD
C7 (over C1) External PTFE cable sheathing with 3mm OD with internal PTFE cable with 1mm OD with 50mm exposed C1 and tip. Available for FOT-L-SD only.

Cable length

Length code Description
M2 2 metres
M5 5 metres
M10 10 metres

Measurement range

Range code Description
R1 Calibrated over full measurement range of -40°C to 250°C (FOT-L-BA) / 300°C (FOT-L-SD); Accuracy ±1°C; Resolution ±0.1°C
R2 Calibrated over 20°C to 85°C; Accuracy ±0.5°C; Resolution ±0.1°C
R3 Calibrated over 20°C to 85°C; Accuracy ±0.3°C (sensor must be paired with a measurement channel); Resolution ±0.1°C
R4 Calibrated over 25°C to 45°C; Accuracy ±0.25°C; Resolution ±0.01°C
R5 Calibrated over -10°C to 120°C; Accuracy ±0.4°C; Resolution ±0.01°C

Connector type

Connector code Description
ST ST connector
SL Sleeve connector
SCA SC/APC connector

Shipping information

The sensor is packaged in a protective plastic box 255mm x 255mm x 30mm weighing 125gms

Place your order before 2pm to select next day delivery. In a hurry? pre 10:30am delivery also available.


The FOT-L-SD and FOT-L-BA are fibre optic temperature sensors perfectly suited for harsh environmental conditions such as in cryogenics, nuclear, microwave, and strong RF applications.

The FOT-L temperature sensors combine all the desired characteristics you would expect from the ideal sensor. These temperature sensors offer accuracy and reliability in extreme temperature and hostile environments.

Both FOT-L temperature sensors feature complete immunity to EMI and RFI, miniature size, built-in safety for hazardous environments, extreme temperature resistance, high precision, and resistance to corrosive environments.

Fibre optic technology provides intrinsic immunity to EMI and RFI. Fibre optic sensors are not electronically active and do not emit nor are they affected by any type of EM radiation, whether it is microwave, RF, or NMR.

Another important advantage of optical fibres is the capability it provides to produce miniature components without compromising the physical characteristics of the bulk material. Optical fibre is optimized in size to provide the smallest possible light path. Thanks to this advantage, fibre optic sensors may feature tip diameters as small as 0.8 mm.

FISO’s fibre optic temperature sensors provide accurate, stable, and repeatable measurements. These measurements are based on variations of the reflected light — when compared to the emitted light — due to thermal expansion of the highly stable glass used within the sensor.

The FOT-L-SD is sheathed with PTFE and has a temperature range from as low as −40°C up to 300°C.

The FOT-L-BA is designed with a much smaller diameter to provide an even faster response time, while able to withstand temperatures of up to 250°C. However, please note that it achieves this fast response time because it has an unprotected sensor tip and is therefore very delicate.

All our temperature sensors are designed to work with FISO’s line of signal conditioners, the FPI-HR, FPI-HS, FTI-10 and UMI.

The fibre optic lead cable can be up to several meters long without affecting the quality or the accuracy of the results.

Temperature range R1 R2 R3 R4 R5
FOT-L-SD -40°C to 300°C 20°C to 85°C 20°C to 85°C 25°C to 45°C -10°C to 120°C
FOT-L-BA -40°C to 250°C 20°C to 85°C 20°C to 85°C 25°C to 45°C -10°C to 120°C
Resolution 0.1°C 0.1°C 0.1°C 0.01°C 0.01°C
Accuracy ±1°C ±0.5°C ±0.3°C ±0.25°C ±0.4°C


Response time  
FOT-L-SD ≤ 1.5 seconds
FOT-L-BA ≤ 0.5 seconds
Bend Radius 2.5cm


  • Microwaves and RF
  • Medical applications
  • Nuclear environments
  • In-situ process monitoring
  • Harsh and hazardous environments
  • High temperature environments
  • Aerospace applications
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