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Water Temperature Sensor Based on Optical Fibre Sensor


It is essential to monitor water temperature to prevent the growth of potentially harmful legionella bacteria. Conventional temperature sensors are often made of metal and are not appropriate for use near or in drinking water. As a result, developing a water-safe temperature sensor is essential. Due to its capacity to monitor temperatures based on the bending of the optical cable and the light escaping from the fiber cable, a polymeric optical fiber sensor was selected as the basis for the design of the water temperature sensor. An optical fiber water temperature sensor requires a transmitter circuit, an Optical Fiber sensor, and a reception circuit.

1.0 Introduction

There is universal agreement that water, particularly the water used daily by humans, is crucial to life on Earth and must be constantly regulated. Since water intended for human consumption must be kept at a temperature of less than 20 degrees Celsius, temperature is one of the most critical parameters to check regularly. As a result, a specialized sensor is required for accurate water temperature readings.

Several different temperature sensors may be used in industrial settings, each with pros and cons in terms of temperature range, quality, reaction time, stability, accuracy, cost, chemical interference, etc.

Although there is no such thing as a perfect temperature sensor, certain guidelines must be followed to select one that will accurately measure the temperature of the target substance (Djaid, 2022). In Table 1, we quickly compare three widely used thermometer sensors in industrial settings.

Comparison of Three Common Temperature Sensors (J. David, 2022)

Table 1: Comparison of Three Common Temperature Sensors (J. David, 2022)

A temperature sensor for drinking water must meet strict criteria to avoid tainting the water with impurities while providing the necessary precision and sensitivity in the allotted amount of time. Traditional temperature sensors, such as those listed in Table 1, are often composed of materials that, with time, may contaminate water, including copper, nickel, aluminum, chromium, silicon, iron, ceramics, and others.

The fiber-optic variety is an essential tool for measuring water temperature since it can transmit data at the speed of light. It has a bandwidth of hundreds of terabits per second. This optical sensor’s most notable and distinctive benefit is its much-increased bandwidth compared to standard metal wires. Features include portability, cheap cost, great precision, complete adaptability, and water-safe materials like plastic or glass (Thyagarajan & Ghatak, 2007). It is also immune to all external electromagnetic interference. In addition, unlike traditional sensors, optical fiber sensors do not need high-tech waterproofing to protect the detecting head, making them the greatest option for water detection due to their inherent stability.

The following are the parts of a sensor device based on optical fibers:

  • Light-emitting diode (LED), laser, or other optical transmitter.
  • Sensing Element may include a sensing head or an optical fiber wire.
  • An optical receiver utilizes a detector (photodiode, phototransistor, etc.) to read the light generated by the detecting area.

The block schematic of an optical fiber sensor is shown in Figure 1.

lock Diagram of Optical Fiber Sensor

Figure 1: Block Diagram of Optical Fiber Sensor

1.1 Problem Statement

Legionella bacteria thrive in water temperatures between 20 and 45 degrees Celsius. However, temperatures in water below 20 degrees Celsius are not favorable for the growth and activation of Legionella bacteria, as these bacteria cannot pose a threat and will be completely inhibited. This makes it crucial to routinely check water temperatures using reliable sensors (J. David, 2022). This project aims to offer a technique for monitoring water temperature utilizing an optical fiber device, which is the primary issue statement. Optical fiber water temperature detection requires three different methods, one of which will be chosen for implementation in this project.

1.2 Aims and Objectives

This research aims to create a novel optical fiber-based water temperature sensor.

The goals of this study include:

• Conducting a thorough literature review on water temperature sensors

• To provide a strategy for employing fiber optics to measure water temperature.

• Each recommended technique suggestion will have three possible answers provided.

• Decide on the best course of action and justify your decision.

1.3 Structure of the Report

This report is organized mostly to discuss the report’s context, problem statement, goals, and objectives. This section discusses the literature, including examples of the many authors’ research on using optical fiber sensors to measure water temperature. Then, relevant theories are used to analyze the optical fiber’s operation and functioning principle for detecting water temperature. Next, we will talk about the solutions presented and why we decided on the one we did. A project strategy is also detailed, along with the report’s progress. The study ends with a conclusion that summarizes the findings and methodology. The report’s layout is seen in Figure 2 below.

Structure of the Report

Figure 2: Structure of the Report

2.0 Literature Review

This section reviews various authors’ literature on using optical fiber sensors for measuring water temperature. This portion of the paper also discusses important ideas about detecting water temperature using optical fiber sensors.

2.1 Existing Research Work

2.1.1 First Existing System (Zhou et al., 2015)

A novel optical-fiber ultrasonic transducer system-based sensor for measuring pure water temperature has been publicly documented. In that study, a technique for measuring ultrasonic time-of-flight (TOF) using a small fiber-optic was developed. As the pulse width of ultrasound lasers can be controlled, the ultrasonic generator can provide a broad frequency range. An ultrasonic generator produces ultrasound waves through an optical fiber to detect temperature, and a hydrophone is used to receive the ultrasound waves. The configuration of the water temperature sensor is shown in Figure 3.

Schematic of the Water Temperature Sensor Setup

Figure 3: Schematic of the Water Temperature Sensor Setup

The experiment employed a 532 ns laser as the optical radiation source and an optical cable with a 400 nm core as the ultrasonic generator. A hydrophone is used as the receiver, as was previously indicated. Figure 3 demonstrated a 5mm 0.1mm gap between the hydrophone and the ultrasonic probe. When the laser emits a pulse, it sends a signal to the DAQ (Data Acquisition Card), which samples the data at 50 MHz. The clear water is scanned by the hydrophone for ultrasonic waves. Due to the hydrophone’s maximum operating temperature of only 50 degrees, the experiment considers a water temperature range of 8 to 45 degrees Celsius. The experimental setup is shown in Figure 4.

Photo of the Experiment Temperature

Figure 4: Photo of the Experiment Temperature

According to the observed data and the proposed connection between temperature and time delay, the delay grows by 0.1 s 0.001 s for every degree of temperature rise, assuming a constant distance of 5 mm between the receiver and the generator. The correlation between temperature and trip time is seen in Figure 5.

Water temperature and the travel time relationship

Figure 5: Water temperature and the travel time relationship

The experiment would be more accurate if a receiver with a greater working temperature range linked to water were used instead of the hydrophone, as the hydrophone’s highest working temperature is 50 degrees. In comparison, the boiling point of water exceeds 100 degrees.

2.1.2 Second Existing System

The second project investigates using a novel dual-mode optical fiber sensor in an underwater temperature and pressure sensor. Industrial applications for the dual-mode optical sensor for measuring water temperature and pressure are currently being explored. Optical fiber sensors that measure water temperature and pressure are being developed using cutting-edge technology. In order to detect and measure water pressure and temperature, it is suggested to couple an in-line MZI sensor with an optical fiber sensor. A theoretical investigation is presented with sensor implementation to measure water pressure and temperature in manufacturing settings. Analysis shows that splicing sensor DMF-MZI between its two segments may readily produce sensors with varying physical lengths of 0.18m, 0.34m, and 1.4m. The sensor structures are constructed to examine this process’s solution, as well as to examine various undersea temperatures and pressure, and to examine, finally, the sensors’ efficacy in detecting these parameters. Changing these characteristics at different depths allows us to see how they change over time. As an additional demonstration of the adaptability of sensors for use in various industrial contexts, this sensor has been tested in both liquid and gaseous environments. The sensor installation is shown in Figure 6’s schematic.

Schematic diagram sensor setup.

Figure 6: Schematic diagram sensor setup.

2.1.3Third Existing System (Haroon, Khadijah Idris, Mohd Zain, Abdul Razak, & Salahuddin, 2021)

In this study, we provide the results of an experiment in which optical and electrical characterizations were used to determine the water temperature.

Figure 7 depicts the experimental setup used for optical characterization. The optical source was a red LED set to produce light at 650 nm, the polymeric temperature sensor was constructed, and the sensor’s output was coupled to an optical power detector. In this experiment, a polymeric optical fiber was heated to convey data to an optical power meter. The fiber was approximately 1 meter long, and the sensing head was about 2 centimeters into the center of the fiber cable.

Optical Characterization Experiment Setup

Figure 7: Optical Characterization Experiment Setup

The receiver was constructed using a practical amplifier of the type LM358P, which converts the radiation that is received into easily interpreted electrical signals, and the key component of the receiver is the photodiode LFD91; the voltmeter will be used for determining the output voltage and track any fluctuations due to temperature changes, as shown in Figure 8.

Electrical characterization experiment setup

Figure 8: Electrical characterization experiment setup

As seen in Figure 9, the outcome of this experiment demonstrates a correlation between temperature and the extracted voltage, as a rise in water temperature would always result in a commensurate voltage increase.

Voltage output against temperature

Figure 9: Voltage output against temperature

The polymeric optical fiber’s unique properties as a flexible, small, light, cheap, and Arduino-operable temperature measurement device for pure water make it exceptional. As a result, if efforts are being made to enhance the water temperature, this monitoring method is ideal.

3.0 Possible and Proposed Solutions

The use of fiber optics to measure water temperature has advantages over other methods since both plastic and glass fibers may be submerged without harming the water’s quality. Glass fiber is regarded to be most suited for this experience because of its brittle flexibility, non-folding nature, and high cost in compared to plastic fiber (Werneck & Allil, 2020). Due to the nature of the experiment, the fiber will unavoidably be folded, necessitating a low-cost, extremely flexible, and non-breakable sensor system.

3.1 Components and Devices for the Solution:

Transmitter Circuit:

  • 555 Timer circuit.
  • An optical LED (SIEMENS SFH 750V)
  • LED Driver circuit using an NPN transistor.

Fibre Optic Sensor:

  • A polymeric Optical Fiber (POF) cable with a PMMA core of 980 μm and a diameter of 1 mm.

Receiver Circuit:

  • Photodiode IF-D91
  • Transimpedance amplifier Circuit
  • Analog to Digital Converter


  • The microcontroller of Arduino Due Board
  • PC Device

Polymeric optical fibers (POF) are the preferred method for measuring water temperature due to their low cost, absolute flexibility, and lightweight; the block diagram of this system can be seen in Figure 10; it is based on the macro-bend of the POF temperature.

Polymeric optical fibers (POF)

This POF uses the fact that macro-bending causes optical fibers to lose some radiance (Pakdeevanich, 2007). Light leakage due to the fiber cable’s bending is, as shown in Figure 11, a critical component of this system’s operation. Therefore, there is a one-to-one correspondence between the water density and the voltage the bending fiber cable receives.

Light leakage

5.0 Conclusion

An intermediate report on using an optical fiber sensor to measure water temperature is offered. Some background information is provided. This report presents the research’s purpose, goals, and problem description, all of which must be resolved via an examination of the answers offered at the end of the study. The general theory related to this issue is explained, considering the experimental procedure and assessing the outcomes. Then the literature review is reviewed to evaluate past and current work undertaken on this research topic.

The feasibility of designing a water temperature sensor circuit has been established using one of the various options. Since bending an optical cable causes radiation losses, a cheap polymeric optical fiber was developed as a solution.


Djaid, D. (2022, Feb 14). Blackboard. Retrieved from Instrumentation and Measurement Module:

Haroon, H., Khadijah Idris, S., Mohd Zain, A., Abdul Razak, H., & Salehuddin, F. (2021). Temperature monitoring using polymer optical fiber with integration to the Internet of Things. ISSN: 2302-9285, 357-363.

  1. K. (2022). Legionella and the Role of Dissolved Oxygen in Its Growth. Water.

LEI, X., DONG, X., LU, C., SUN, T., & T. V. GRATTAN, K. (2020). Underwater Pressure and Temperature Sensor. IEEE, 146463-146469.

Pakdeevanich, P. (2007). Optical fiber sensor based on a polymer optical fiber macro bend to study the thermal expansion of metals.

Rajan, G. (2015). Optical Fiber Sensors Advanced Techniques and Applications. Ginu Rajan.

Thyagarajan, K., & Ghatak, A. (2007). Fiber optic essentials. Canada: John Wiley & Sons.

Werneck, M. M., & Allil, R. C. (2020). Plastic Optical Fiber Sensors. Taylor & Francis Group, LLC.

Zhou, J., Wu, N., Wang, X., Liu, Y., Ma, T., Coxe, D., & Cao, C. (2015). Water temperature measurement using a novel fiber optic ultrasound transducer system. IEEE, pp. 2316–2318.


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