winding temperature measurement using fiber optics sensor

1. Winding temperature measurement using fiber optic sensors enables real-time, precise, and reliable monitoring of transformer hot spot temperature, enhancing safety, efficiency, and asset life.
2. Fiber optic temperature sensors offer immunity to electromagnetic interference, distributed measurement, and direct embedding in windings, making them superior to traditional RTD or thermocouple solutions.
3. This guide provides clear answers to all frequently asked technical, working principle, comparison, and application questions surrounding fiber optic winding temperature measurement.
4. At the end, a table lists the top 10 global fiber optic sensor manufacturers for transformer windings, featuring FJINNO (founded in 2011) as the leading brand.

Table of Contents

1. What are optical fiber sensors for temperature measurement?
2. What is OTDR temperature measurement?
3. What is the temperature sensor for transformer winding?
4. Can temperature be directly measured using a sensor?
5. Top 10 Winding Fiber Optic Sensor Manufacturers

What are optical fiber sensors for temperature measurement?

What are the advantages of fiber optic temperature sensors?

1. Electromagnetic Immunity:
   Fiber optic temperature sensors are fully immune to electromagnetic interference (EMI) and radiofrequency interference (RFI). This makes them exceptionally reliable in high-voltage environments such as power transformers, where traditional electrical sensors often fail or give inaccurate readings.
2. Direct Hot-Spot Measurement:
   Unlike surface-mounted or oil-based sensors, fiber optic sensors can be embedded directly into transformer windings. This allows for direct and accurate monitoring of the hottest spots, which is crucial for transformer health and operational safety.
3. Multipoint Capability:
   the entire winding length or at several critical locations within the transformer.
4. Long-Term Stability and Safety:
   Optical fibers are non-conductive and chemically inert, which means they do not degrade in harsh environments and pose no risk of electrical shorting or arcing inside transformers.
5. High Accuracy and Fast Response:
   Fiber optic temperature sensors offer high accuracy (often ±0.1°C to ±1°C) and fast response times, making them ideal for protection and control scenarios where rapid thermal changes must be detected.

What is the optical measurement of temperature?

Optical measurement of temperature refers to the use of light—typically guided through an optical fiber—to sense thermal changes. Instead of relying on electrical resistance or voltage, these systems use variations in light intensity, wavelength, fluorescence decay, or scattering within the fiber. The temperature-sensitive region can be created by doping the fiber with special materials or applying coatings that respond to heat in a measurable, repeatable way.

Which sensors are used to measure temperature?

The main sensors for temperature measurement include fiber optic sensors (such as fluorescent fiber optic sensors, fiber Bragg grating (FBG) sensors, and distributed temperature sensing (DTS) systems), resistance temperature detectors (RTDs), thermistors, thermocouples, and infrared thermometers. Among these, fiber optic sensors are uniquely qualified for transformer winding monitoring due to their immunity to EMI, safety, and ability to be embedded in windings.

What is the temperature rating of optical fiber?

The temperature rating of optical fiber sensors typically ranges from -40°C to +250°C, depending on the fiber material, coatings, and sensor design. Fluorescent fiber sensors can maintain accuracy and stability across this entire range, making them suitable for power transformer and industrial applications. Some specialty fibers can even withstand higher temperatures for short periods.

How does a fiber sensor measure temperature?

1. Fluorescent Fiber Principle:
   Fluorescent fiber optic temperature sensors use a small probe containing a fluorescent material (often a rare earth-doped glass). When excited by a light pulse, the material emits light at a specific wavelength. The decay time or intensity of this emitted light varies with temperature. By measuring this property through the fiber, the sensor system can accurately determine the temperature at the probe location.
2. FBG Principle:
   Fiber Bragg Grating sensors reflect a specific wavelength of light. When the temperature changes, the grating spacing inside the fiber changes, causing a shift in the reflected wavelength. This wavelength shift is proportional to the temperature change and is detected by an optical interrogator.
3. DTS Principle:
   Distributed temperature sensing (DTS) systems use the Raman or Brillouin scattering effect. A laser pulse is sent down the fiber; the backscattered light changes as a function of local temperature. By analyzing the time delay and spectrum of the returning signal, the system provides a temperature profile along the entire length of the fiber.

What do optical sensors measure?

Optical sensors are capable of measuring a range of physical parameters, including temperature, strain, pressure, vibration, and displacement. In transformer applications, temperature and strain measurement are most relevant. The underlying principle is always based on detecting a change in an optical property (such as intensity, wavelength, phase, or polarization) caused by the external parameter of interest.

What sensor applications need optical fiber?

Optical fiber sensors are essential in environments where traditional electrical sensors would be unreliable or unsafe due to strong EMI, high voltages, chemical exposure, or the need for very long-distance sensing. Common applications include power transformer winding temperature monitoring, high-voltage switchgear, generator windings, oil and gas pipelines, fire detection in tunnels, and medical equipment.

What is a typical equipment generally used to measure?

A complete fiber optic temperature measurement system typically includes: (1) one or more fiber optic temperature probes (such as fluorescent or FBG probes), (2) an optical interrogator or signal analyzer to send and receive light, and (3) a data acquisition or SCADA system to process and display temperature readings. Modern systems are compact, robust, and often support multiple channels for comprehensive asset monitoring.

Why is a thermocouple used?

Thermocouples are widely used in industry because they are simple, inexpensive, and can measure a very broad temperature range (from -200°C to +1700°C for some types). They generate a voltage proportional to temperature difference at their junction, which is easy to measure. However, they suffer from EMI, limited accuracy, and cannot be embedded inside transformer windings like fiber sensors.

What is a thermocouple in physics?

In physics, a thermocouple consists of two dissimilar metal wires joined at one end. When the junction is heated or cooled, a voltage is produced that can be correlated to temperature. This thermoelectric effect (Seebeck effect) is the fundamental principle behind thermocouple temperature measurement.

How does a temperature sensor work in IoT?

In Internet of Things (IoT) systems, temperature sensors (including fiber optic types) collect temperature data and transmit it via wired or wireless networks to a central controller or cloud platform. This enables remote monitoring, predictive maintenance, and automated alarms for temperature anomalies in smart grids, industrial automation, and building management.

What is a temperature sensor and humidity sensor?

A temperature sensor detects changes in ambient or contact temperature, converting thermal signals into electrical or optical signals. A humidity sensor measures the amount of water vapor in the air, usually by detecting changes in capacitance or resistance of a hygroscopic material. Both types of sensors are critical in environmental monitoring, industrial automation, and smart facility management.

What is OTDR temperature measurement?

What is the difference between OLTS and OTDR?

OLTS (Optical Loss Test Set) and OTDR (Optical Time Domain Reflectometer) are both used for fiber optic testing, but their purposes differ. OLTS measures the total optical power loss along a fiber link between two points, giving an overall insertion loss value. OTDR, on the other hand, injects light pulses into the fiber and analyzes the backscattered signal as a function of distance. This allows OTDR to locate faults, splices, bends, and breaks, and to provide a detailed trace of the fiber’s attenuation profile. In temperature measurement, OTDR is essential for distributed sensing along the fiber length.

What is the temperature range of fiber optic?

The typical working temperature range for fiber optic sensors is from -40°C to +250°C. However, the exact range depends on the fiber material, coatings, and sensor construction. Some specialized optical fibers can withstand higher temperatures, but for transformer winding monitoring, the standard range is more than sufficient, even under overload or fault conditions.

Can an OTDR be used to check the condition of an optical fiber cable?

Yes, an OTDR is a vital tool for checking the health of optical fiber cables. It can detect and locate fiber breaks, microbends, splices, and connectors and measure the loss at each point. In distributed temperature sensing systems, OTDR also analyzes the backscatter data to provide a continuous thermal profile along the cable, identifying hot spots or temperature anomalies.

What is the OTDR test used to measure?

1. Fiber Integrity: The OTDR test measures the condition and continuity of the optical fiber, locating faults, breaks, and excessive losses.
2. Distributed Temperature: In DTS applications, OTDR measures the intensity and timing of backscattered light (Raman or Brillouin scattering) to determine temperature at every point along the fiber.
3. Event Locations: It pinpoints the location of splices, connectors, and defects, which is useful for maintenance and troubleshooting.

What is the difference between OTDR and LSPM?

LSPM (Light Source and Power Meter) is a basic method for measuring end-to-end loss in a fiber optic link. It does not provide information about the location of losses. OTDR offers a time- and distance-resolved profile, showing exactly where within the fiber each loss occurs. For temperature measurement, only OTDR-based systems can provide true distributed temperature data.

What is distributed temperature sensing fiber optic cable?

Distributed Temperature Sensing (DTS) fiber optic cables enable temperature to be measured continuously along their length. DTS technology typically uses the Raman or Brillouin effect: a laser pulse is sent through the fiber, and the backscattered light varies according to temperature at each point. This allows one cable to function as thousands of temperature sensors, making DTS ideal for monitoring transformer windings, power cables, pipelines, and tunnels.

What is the difference between OTDR and OTDR?

All OTDR instruments work on the same principle—injecting light pulses and analyzing backscattered signals. Differences may exist in the wavelength used (single-mode vs. multi-mode), dynamic range, resolution, and whether the instrument is optimized for communication or sensing applications. For temperature measurement, specialized OTDR systems are used in DTS equipment.

What is DTS temperature measurement?

1. Principle: DTS (Distributed Temperature Sensing) sends light pulses along an optical fiber. The backscattered Raman or Brillouin signal changes depending on the local temperature at each point along the fiber.
2. Result: The system produces a real-time temperature profile along the entire cable, allowing operators to monitor the thermal status of large or complex assets with a single sensor cable.
3. Applications: DTS is widely used in transformer windings, oil and gas pipelines, fire detection, and industrial plants where continuous temperature monitoring is required.

What is possible to know when with an OTDR?

1. Cable Health: An OTDR can reveal the presence and location of fiber breaks, splices, bends, and connectors.
2. Loss Profile: It shows the cumulative and localized loss along the fiber, helping to identify weak points.
3. Distributed Temperature: In DTS mode, it provides temperature measurements at every point along the cable, enabling early detection of hot spots or abnormal thermal conditions.

What is the range of the fiber optic temperature sensor?

The sensing range of fiber optic temperature sensors depends on the interrogation technology. For point sensors like FBG or fluorescence probes, the effective range is up to several hundred meters, limited by the fiber and interrogator. For DTS systems, the range can extend from 1 km up to 30 km or more, although spatial resolution and accuracy may decrease with length. In transformer applications, the required range is usually less than 20 meters.

What is the maximum range of OTDR?

High-performance OTDRs can analyze fiber links up to 100 kilometers or more, though most transformer or industrial temperature monitoring applications require much shorter fiber runs. The maximum useful range depends on fiber type, signal attenuation, and instrument sensitivity.

Is OTDR acceptable for certification?

Yes. OTDR is the industry standard for certifying new and existing fiber optic installations. It provides documentation of fiber health, splice quality, and loss points, which is essential for both communication and sensing (including distributed temperature sensing) applications.

How does fluorescent fiber optic temperature sensing work and what are its advantages?

1. Principle of Fluorescent Fiber Sensing:
   Fluorescent fiber optic temperature sensors use a probe containing a fluorescent material—such as a rare-earth doped glass or a phosphorescent ceramic—attached to the tip of an optical fiber. When a pulse of excitation light is sent through the fiber, the fluorescent material absorbs the energy and emits light at a longer wavelength (fluorescence). The decay time (lifetime) of this emission is highly dependent on the local temperature. By precisely measuring the decay time or intensity of the emitted light, the temperature at the probe can be determined with high accuracy.
2. Advantages of Fluorescent Fiber Sensors:
   1. Direct Hot-Spot Measurement: The sensors can be embedded directly inside transformer windings, allowing for true hot-spot temperature monitoring—critical for transformer protection and asset management.
   2. Immunity to EMI and Harsh Environments: The non-electrical nature of fiber optics ensures that the temperature measurement is unaffected by strong electromagnetic fields and electrical surges.
   3. High Accuracy and Fast Response: Fluorescent fiber sensors offer high accuracy (often better than ±1°C) and respond rapidly to temperature changes, supporting real-time protection systems.
   4. Long-Term Stability and Reliability: The optical and chemical properties of the fluorescent probe do not drift over time, ensuring consistent and maintenance-free operation in oil, gas, or other harsh transformer environments.
   5. Multipoint and Distributed Measurement: Multiple fluorescent probes can be attached to a single interrogator, allowing simultaneous monitoring of several locations within the same transformer.
3. Application in Transformer Winding Temperature Monitoring:
   1. Installation: During transformer manufacturing, fluorescent fiber probes are carefully positioned in the winding hot-spot regions. The fiber is routed out of the tank to the interrogator, which is located outside the transformer.
   2. Monitoring: The interrogator sends excitation pulses and reads the fluorescence response in real time, displaying the temperature on a control panel or transmitting it to SCADA or asset management systems.
   3. Protection and Control: If the winding temperature approaches alarm or trip thresholds, the system can trigger cooling fans, alarms, or even disconnect the transformer to prevent catastrophic failure.

What is the temperature sensor for transformer winding?

How to measure transformer winding temperature?

1. Direct Embedding: The most accurate method is embedding fiber optic temperature sensors—especially fluorescent probes—directly into the winding’s hottest spots during transformer assembly. This enables real-time monitoring of the actual hot-spot temperature, which is a key indicator of insulation health and transformer longevity.
2. Indirect Estimation: Traditional methods estimate winding temperature using a combination of top-oil temperature and load current, but these can miss rapid or localized heating. Fiber optic sensors eliminate this guesswork by providing direct and immediate hot-spot data.
3. Data Integration: The measured temperature is fed into transformer control, protection, and SCADA systems for automated cooling, alarms, and condition monitoring.

What is the working principle of winding fiber optic temperature sensor?

The working principle depends on the sensor type. For fluorescent fiber optic sensors, a probe at the winding hot-spot is excited by a light pulse via the fiber. The probe’s fluorescent material emits light with a decay time that varies with temperature. This decay signal is sent back through the fiber and interpreted by the interrogator to extract the exact winding temperature. Fiber Bragg Grating (FBG) sensors rely on changes in the reflected wavelength, also proportional to temperature. Both methods are immune to electromagnetic interference and safe for direct embedding in high-voltage windings.

What is the standard winding temperature for a transformer?

The standard maximum winding hot-spot temperature for most power transformers is 120°C to 140°C, depending on insulation class (typically Class A, B, or F). Exceeding this temperature accelerates insulation aging, reduces transformer life, and increases risk of failure. For each 6–8°C rise over the recommended hot-spot, insulation life is roughly halved; hence, accurate hot-spot monitoring is critical.

How is a RTD for motor winding temperature?

RTDs (Resistance Temperature Detectors) are sometimes used for motor or generator windings, but they are rarely embedded within transformer windings due to their electrical nature and susceptibility to EMI. They are less accurate than fiber optic sensors for transformer hot-spot monitoring. RTDs are, however, useful for surface or oil temperature measurement.

How do FBG (Fiber Bragg Grating) sensors work?

FBG sensors are a type of fiber optic temperature sensor. A periodic grating is inscribed into the fiber core, reflecting a specific wavelength of light. When the local temperature changes, the grating spacing alters, causing a shift in the reflected wavelength. The interrogator detects this shift and converts it into a temperature reading. FBG sensors can be multiplexed along a single fiber, allowing multiple points to be monitored simultaneously.

Which type of temperature sensor is best for 1st vs. 2nd motor windings?

For both primary and secondary windings in transformers or motors, fiber optic temperature sensors—especially fluorescent or FBG types—are preferred due to direct measurement, electrical safety, and immunity to electromagnetic noise. For less critical or surface monitoring, RTDs or thermistors may be sufficient.

What is expected output of temperature sensor?

Fiber optic temperature sensors output either an optical signal (such as fluorescence decay or wavelength shift), which is then converted by the interrogator into a digital temperature value. This value can be displayed locally, transmitted to SCADA, or used for automated protection logic.

What can be used to check the winding of a temperature sensor?

The health and calibration of winding temperature sensors can be checked using the fiber optic interrogator. Modern interrogators can diagnose sensor connection, signal quality, calibration drift, and provide self-diagnostics for the entire monitoring system. Regular verification ensures reliable operation over the transformer’s life.

What is a winding mechanism?

In transformers or motors, a winding mechanism refers to the process and structure of winding insulated copper or aluminum conductors into coils. The windings carry current, produce magnetic flux, and are the hottest parts of the transformer—thus requiring precise temperature monitoring to prevent overheating and insulation breakdown.

What is the role of winding temperature indicator in transformer?

The winding temperature indicator displays the measured hot-spot temperature. It is essential for transformer protection, as it allows operators or automation systems to trigger alarms, activate cooling, or disconnect the transformer before dangerous overheating occurs. Modern indicators integrate with digital control systems and can also record temperature trends for predictive maintenance.

Where is winding temperature sensor used?

Winding temperature sensors are used in power transformers, distribution transformers, generator and motor windings, reactors, and sometimes in industrial furnaces. Their main function is to provide continuous, direct, and accurate hot-spot temperature data for safety, reliability, and asset management.

What is winding temperature?

Winding temperature is the actual temperature at the hottest point inside the transformer’s windings. This value is the best indicator of insulation health and transformer aging, as excessive temperatures accelerate degradation and risk catastrophic failure. Accurate winding temperature monitoring is a critical parameter for modern transformer management.

Can temperature be directly measured using a sensor?

How to use PT100 temperature sensor?

The PT100 is a platinum RTD (Resistance Temperature Detector) with a nominal resistance of 100 Ω at 0°C. To use it, connect the PT100 to a measurement circuit (usually a Wheatstone bridge or dedicated RTD module). As the temperature rises, the resistance increases linearly. The voltage drop across the sensor is measured and converted to temperature. PT100s are widely used for industrial temperature measurements but are less suitable for embedding in transformer windings due to their electrical nature and EMI susceptibility.

What is the difference between thermistor and a RTD sensor?

RTDs use pure metals (typically platinum) and have a nearly linear and predictable resistance-temperature relationship, offering high accuracy and stability. Thermistors use semiconductor materials, providing much greater sensitivity (large resistance changes for small temperature shifts), but their response is highly nonlinear and they have a narrower temperature range. RTDs are preferred for precise, wide-range measurements; thermistors are often used where high sensitivity is needed within a limited range.

What are the three ways that temperature sensors can be tested?

1. Calibration Bath: Place the sensor in a temperature-controlled bath and compare its reading to a certified reference thermometer at various set points.
2. Reference Comparison: Install the sensor alongside a standard sensor in the application environment and compare readings over time to assess accuracy.
3. Electrical or Optical Simulation: For RTDs, use precision resistors to simulate known temperatures; for fiber optics, use optical signal simulators or reference probes to verify system response.

What is the difference between thermocouple and RTD?

A thermocouple generates a voltage based on the temperature difference between two different metal junctions (the Seebeck effect). It works across a very wide temperature range and is durable but less accurate and more prone to noise. An RTD operates on the principle that the resistance of a pure metal (like platinum) increases with temperature. RTDs are more accurate, stable, and repeatable but have a narrower range and require a current source for measurement.

Which sensor is used to detect skin temperature?

Thermistors and infrared (IR) sensors are most commonly used for skin temperature measurement in medical and wearable applications. These sensors offer high sensitivity and quick response, but are not suitable for transformer winding hot-spot monitoring.

How does the SHIMT sensor work?

While SHIMT is not a standard sensor acronym, in general, modern temperature sensors work by converting a physical property change (resistance, voltage, wavelength, intensity) directly into an electrical or optical signal that can be measured and interpreted as temperature.

How do you measure temperature directly?

Direct temperature measurement involves placing a sensor—fiber optic probe, RTD, thermistor, or thermocouple—in physical or thermal contact with the point of interest. The sensor’s signal is then processed to provide a real-time temperature reading. For transformer windings, fiber optic probes are embedded in the windings for the most accurate and responsive results.

How does a 2-wire temperature sensor work?

In a 2-wire sensor setup, both measurement and excitation current pass through the same wires, which introduces a small measurement error due to lead resistance. This is acceptable for short runs and moderate accuracy. For high-precision applications (such as transformer winding temperature), 3-wire or 4-wire configurations or optical sensors are preferred.

What is the difference between thermocouple and thermistor sensor?

Thermocouples generate a voltage based on temperature difference at two metal junctions, providing a wide measurement range. Thermistors use semiconductor materials, showing a large resistance change with temperature but only over a limited range. Thermistors are more accurate over short ranges, while thermocouples are robust for extreme temperatures.

How to measure temperature using RTD?

Pass a precise, constant current through the RTD and measure the resulting voltage drop. This resistance is proportional to temperature and is converted using a calibration curve. For direct winding hot-spot measurement, fiber optic sensors are generally preferred over RTDs due to safety and immunity to EMI.

What are the different types of non contact temperature sensors?

Non-contact temperature sensors measure temperature remotely without touching the sample. Common types include infrared (IR) thermometers, thermal imaging cameras, and optical pyrometers. These are useful for surface temperature monitoring but not suitable for internal transformer windings, where fiber optic probes are required.

How to make a temperature sensor?

For a basic electronic temperature sensor, use a thermistor or RTD connected to a microcontroller or measurement circuit. For a fiber optic temperature sensor, use a length of optical fiber and a temperature-sensitive probe (fluorescent or FBG), and connect it to an optical interrogator. For precise and reliable transformer winding monitoring, commercial fiber optic solutions are recommended due to their calibration, durability, and integration features.

Top 10 Winding Fiber Optic Sensor Manufacturers

Fiber optic temperature sensor, Intelligent monitoring system, Distributed fiber optic manufacturer in China