New Products and Techniques

Fiber-Optic Distributed Temperature Sensing System
FTS3500
The OPTHERMO fiber-optic distributed temperaturesensing system is a product of Sumitomo ElectricIndustries, Ltd. and is one of the component technologies
used in infrastructure monitoring and maintenance systems.
There are currently two models in the OPTHERMO lineup:
the FTR3000 (a short distance model at an accessible price)and the FTR3000X (a long-distance and high-performancemodel at a higher price). By limiting its functions, theFTR3000 has offered the most reasonable price in Japanamong equivalent products. However, it is 10 years since
FTR3000 was introduced to the market, and therefore it
was time for the product to be updated with functional
enhancements and other changes. We have now developed
a successor model, the FTS3500, which offers better
performance while still maintaining the lowest price inJapan.

2. Features of OPTHERMOOPTHERMO can measure both distance and temperature along an optical fiber cable, by utilizing the opticalfiber itself as a thermal sensor. As OPTHERMO canmeasure the thermal distribution along an optical fiber
cable that has been laid out over a long distance, it isutilized as a thermal monitoring system that can detect
thermal abnormalities in a wide variety of infrastructures,
including power cables and tunnels, and in smaller facilities such as belt conveyers. With regard to thermal monitoring for power cables in particular, OPTHERMO is often
used together with the dynamic rating system (DRS),
which calculates a power cable conductor’s temperatureand maximum allowable load current in real time based on
the OPTHERMO data and the load current. Currently,
investment in infrastructures is active in emerging markets,and thus demand for OPTHERMO is expected to grow.
OPTHERMO utilizes the optical time-domain reflectometer (OTDR) technology that is widely used in opticalfiber testing. OPTHERMO injects light pulse into theoptical fiber, and then extracts the Raman back-scattering
light of which intensity varies by the temperature where thescattering occurs. The temperature can be calculated basedon the ratio of the Stokes and anti-Stokes light intensity(Fig. 1). At the same time, the distance is calculated fromthe time between the injection of light pulse into the opticalfiber and the arrival of the Raman-scattering light. The
intensity of the Raman-scattering light is extremely weak—less than 1/100,000 of the light source. To detect the62 · SEI TECHNICAL REVIEW · NUMBER 89 · OCTOBER 2019

OPTHERMO

CPUScattering

Light pulse

Lightsource

Distance (time)

Photo
detector

Optical ﬁber

Back-scattering light spectrum
Rayleigh-scattering lightIntensity

1. Outline

Raman-scatteringlight

Brillouin-scatteringlight

Anti-Stokes lightHightemperatureLow
temperature

Stokes light

Wavelength

Fig. 1. OPTHERMO measurement mechanismRaman-scattering light effectively, OPTHERMO uses alarge core diameter graded-index (GI) fiber, which has highcoupling efficiency, as its optical fiber thermal sensor. TheFTS3500 is designed to be exclusively used with this GIfiber. Note that we also offer different product lineups that
support single-mode (SM) fiber designed for opticalcommunications as some customers prefer to use their
existing optical cables for monitoring purposes.

3. Features of the FTS3500
Table 1 shows the specifications of the FTS3500 andits predecessor, the FTR3000. As the FTS3500 may bechosen to upgrade an existing FTR3000, the casing dimensions and the interfaces of the FTS3500 are compatible
with FTR3000. The external appearance of the FTS3500 isshown in Photo 1.
In the course of developing the FTS3500, the technologies gained through development of the FTR3000X, theexisting higher model, have been incorporated into theFTS3500 to achieve a better spatial resolution andsampling interval. The spatial resolution is the minimum
distance needed to detect temperature changes and theperformance improvement of this function is particularlysignificant. Figure 2 provides a definition of the spatial

New Products and Techniques

Table 1. Specification of the FTR3000 and FTS3500
FTR3000

FTS3500

Operation temperature [°C]

0 - 40Same as the left

Power supply voltage [V]DC:10.5 - 13.5
AC: 90 - 264

Same as the left

Dimension W×D×H [mm]300×160×37

Same as the left

Weight [kg]

2.5

2.0

Optical fiber type

GI 50/125

Same as the left

Measurement range [m]2200Same as the left

Sampling interval [m]1.00.25/0.5/1.0

Temperature accuracy*1@2 km [°C]

≤ ±1.0 (Typ)≤ ±2.0 (Max)Same as the left

Spatial resolution [m]3.0

1.0/1.5/3.0

Temperature resolution*2@2 km [°C]

≤ 1.0 (Typ)≤ 2.0 (Max)Same as the left

*1 Temperature accuracy: Maximum Deviation between true temperature and average value of 50
temperature OPTHERMO measured.
*2 Temperature resolution: One standard deviation of 50 temperature OPTHERMO measured.

meter in the new model. In the FTR3000, the samplinginterval was fixed at 1.0 meter and now the FTS3500
offers a range of sampling intervals of 0.25, 0.5, and 1.0
meter in the same way as the FTR3000X. We were able toconfirm that the FTS3500’s functions were equivalent toor better than those of the FTR3000, and that it is a trustworthy upgrading of the FTR3000 or equivalent thirdparty products.

4. Conclusion
We have developed the OPTHERMO FTS3500, asuccessor model to the FTR3000. The dimensions andinterfaces of the FTS3500 are compatible with theFTR3000, and, therefore, the FTS3500 can be upgradedfrom the older model without adjustment. The priceremains as the lowest in Japan, which was one of thesignificant benefits of the FTR3000. In terms of performance, the new model offers temperature detection inmuch finer intervals compared to its predecessor throughimprovements in the spatial resolution and samplinginterval. We plan to actively promote this product for
general long-distance temperature monitoring, as withprevious models, but also for a wider range of purposessuch as for belt conveyers, which need temperature detection in smaller intervals, or for fire detection in tunnels.
• OPTHERMO is a trademark or registered trademark of Sumitomo ElectricIndustries, Ltd.

Photo 1. External appearance of FTS3500

Temperature

Spatial resolution
60℃

90%

Sampling interval
10%： Measurement results： Actual temperature change20℃

Distance
Fig. 2. Spatial resolution

resolution. There has been great demand for an improvement in the spatial resolution and this was one of the major
functional enhancements required for the FTS3500. By
narrowing the pulse width of the input light, the spatial
resolution that used to be approximately 3.0 meters inconventional models was significantly shortened to 1.0

SEI TECHNICAL REVIEW · NUMBER 89 · OCTOBER 2019 · 63