Temperature Sensors Types, How It Works, & Applications

1. GUIDE TO TEMPERATURE SENSORS TYPES, HOW IT WORKS & APPLICATIONS

2. HOW DOES TEMPERATURE SENSOR WORK? 1 5 INTRODUCTION WHAT ARE THE TEMPERATURE SENSORS? WHAT ARE THE DIFFERENT TEMPERATURE SENSORS? 2 6 TABLE OF CONTENT WHERE IS THE TEMPERATURE SENSOR USED? 3 7 WHAT DO TEMPERATURE SENSORS DO? ADVANTAGES OF ENCARDIO RITE’S TEMPERATURE SENSOR 4 8 WHAT IS A TEMPERATURE SENSOR USED FOR?

3. 1 INTRODUCTION Temperature sensors are a simple instrument that measures the degree of hotness or coolness and converts it into a readable unit. Temperature sensors are designed to keep a regular check on concrete structures, bridges, railway tracks, soil, etc.

4. 2 WHAT ARE THE TEMPERATURE SENSORS? A temperature sensor is a device, typically, a thermocouple or resistance temperature detector, that provides temperature measurement in a readable form through an electrical signal. Temperature meters are used in the geotechnical field to monitor concrete, structures, soil, water, bridges etc. for structural changes in them due to seasonal variations. A thermocouple (T/C) is made from two dissimilar metals that generate an electrical voltage in direct proportion with the change in temperature. An RTD (Resistance Temperature Detector) is a variable resistor that changes its electrical resistance in direct proportion with the change in the temperature in a precise, repeatable and nearly linear manner.

5. 3 WHAT DO TEMPERATURE SENSORS DO? A temperature sensor is a device that is designed to measure the degree of hotness or coolness in an object. The working of a temperature meter depends upon the voltage across the diode. The cooler the temperature, lesser will be the resistance, and vice-versa. The resistance across the diode is measured and converted into readable units of temperature (Fahrenheit, Celsius, Centigrade, etc.) and, displayed in numeric form over readout units. In geotechnical monitoring field, these temperature sensors are used to measure the internal temperature of structures like bridges, dams, buildings, power plants, etc.

6. 4 WHAT IS A TEMPERATURE SENSOR USED FOR? In geotechnical monitoring, temperature sensors measure the heat of hydration in mass concrete structures. Temperature sensors are also be used to monitor the migration of groundwater or seepage. The most common area where temperature sensor is used is while curing the concrete because it has to be relatively warm in order to set and cure properly. The seasonal variations cause structural expansion or contraction thereby, changing its overall volume.

7. 5 HOW DOES TEMPERATURE SENSOR WORK? The basic principle of working of the temperature sensors is the voltage across the diode terminals. If the voltage increases, the temperature also rises, followed by a voltage drop between the transistor terminals of base and emitter in a diode. Encardio-Rite has a vibrating wire temperature sensor that works on the principle of stress change due to temperature change. The vibrating wire temperature sensor primarily consists of a magnetic, high tensile strength stretched wire, the two ends of which are fixed to any dissimilar metal in a manner that any change in temperature directly affects the tension in the wire and, thus, its natural frequency of vibration.

8. 5 HOW DOES TEMPERATURE SENSOR WORK? The change in temperature is sensed by the specially built Encardio-rite vibrating wire sensor and is converted to an electrical signal which is transmitted as a frequency to the read-out unit. The frequency, which is proportional to the temperature and in turn to the tension ‘σ’ in the wire, can be determined as, f = 1/2 [σg/ρ] / 2l Hz Where: σ = tension of the wire g = acceleration due to gravity ρ = density of the wire l = length of wire

9. 6 WHAT ARE THE DIFFERENT TYPES OF TEMPERATURE SENSORS? The two main types of temperature sensors are: • Contact Type Temperature Sensors There are a few temperature meters that measure the degree of hotness or coolness in an object by being in direct contact with it. Such temperature sensors fall under the category contact-type. They can be used to detect solids, liquids or gases over a wide range of temperatures. • Non-Contact Type Temperature Sensors These types of temperature meters are not in direct contact of the object rather, they measure the degree of hotness or coolness through the radiation emitted by the heat source. the category contact-type. They can be used to detect solids, liquids or gases over a wide range of temperatures.

10. 6 WHAT ARE THE DIFFERENT TYPES OF TEMPERATURE SENSORS? Thermostat A thermostat is a contact type temperature sensor consisting of a bi-metallic strip made up of two dissimilar metals such as aluminium, copper, nickel, or tungsten. The difference in the coefficient of linear expansion of both the metals causes them to produce a mechanical bending movement when it’s subjected to heat.

11. 6 WHAT ARE THE DIFFERENT TYPES OF TEMPERATURE SENSORS? Thermistors Thermistors or thermally sensitive resistors are the ones that change their physical appearance when subjected to change in the temperature. The thermistors are made up of ceramic material such as oxides of nickel, manga- nese or cobalt coated in glass which allows them to deform easily. Most of the thermistors have a negative temperature coefficient (NTC) which means their resistance decreases with an increase in the temperature. But, there are a few thermistors that have a positive temperature coefficient (PTC) and, their resistance increases with a rise in the temperature.

12. 6 WHAT ARE THE DIFFERENT TYPES OF TEMPERATURE SENSORS? Resistive Temperature Detectors (RTD) RTDs are precise temperature sensors that are made up of high-purity conducting metals such as platinum, copper or nickel wound into a coil. The electrical resis- tance of an RTD changes similar to that of a thermistor.

13. 6 WHAT ARE THE DIFFERENT TYPES OF TEMPERATURE SENSORS? Thermocouples A thermocouple usually consists of two junctions of dissimilar metals, such as copper and constantan that are welded or crimped together. One of these junctions, known as the Cold junction, is kept at a specific temperature while the other one is the measuring junction, known as the Hot junction. On being subjected to temperature, a voltage drop is developed across the junction.

14. 6 WHAT ARE THE DIFFERENT TYPES OF TEMPERATURE SENSORS? Negative Temperature Coefficient (NTC) Thermistor A thermistor is basically a sensitive temperature sensor that reacts precisely to even the minute temperature changes. It provides a huge resistance at very low temperatures. This means, as soon as the temperature starts increasing, the resistance starts dropping quickly. Even a small temperature change is displayed accurately by the Negative Tempera- ture Coefficient (NTC) Thermistor Because of this exponential working principle, it requires linearization. They usually work in the range of -50 to 250 °C.

15. 6 WHAT ARE THE DIFFERENT TYPES OF TEMPERATURE SENSORS? Semi-conductor based sensors A semiconductor-based temperature sensor works with dual integrated circuits (ICs). They contain two similar diodes with temperature-sensitive voltage and current characteristics to measure the temperature changes effectively. They give linear output but are less accurate and exhibit the slowest responsiveness (5 s to 60 s) across the narrowest temperature range (-70 °C to 150 °C).

16. 6 WHAT ARE THE DIFFERENT TYPES OF TEMPERATURE SENSORS? Model ETT-10V Vibrating Wire Temperature Sensor The Encardio-rite Model ETT-10V vibrating wire temperature meter is used for the measurement of internal temperature in concrete structures or water. It has a resolution of better than 0.1°C and works similar to that of Thermocouple Tempera- ture Sensors. It also has a high temperature range from -20oto 80o C.

17. 6 WHAT ARE THE DIFFERENT TYPES OF TEMPERATURE SENSORS? Model ETT-10TH Resistance Thermistor Probe The Encardio-rite Model ETT-10TH resistance temperature probe is a low mass waterproof temperature probe for measurement of temperature between –20 to 80°C and has a fast response time. Model ETT-10TH resistance temperature probe is specially designed for the mea- surement of surface temperatures of steel & measurement of the surface tempera- ture of concrete structures. ETT-10TH can be embedded in concrete for measurement of bulk temperature inside the concrete and can even work submerged underwater. ETT-10TH resistance temperature probes are fully interchangeable.

18. 6 WHAT ARE THE DIFFERENT TYPES OF TEMPERATURE SENSORS? Encardio-rite’s model EDI-51V vibrating wire indicator when used with ETT-10TH directly shows the probe temperature in degree Celsius.

19. 6 WHAT ARE THE DIFFERENT TYPES OF TEMPERATURE SENSORS? Model ETT-10PT RTD Temperature Probe The ETT-10PT RTD (Resistance Temperature Detector) temperature probe consists of a ceramic resistance element (Pt. 100) with DIN IEC 751 (former DIN 43760) Euro- pean curve calibration. The resistance element is housed in a closed-end robust stainless steel tubing which protects the element against moisture.

20. 6 WHAT ARE THE DIFFERENT TYPES OF TEMPERATURE SENSORS? Encardio-Rite Thermocouple https://www.encardio.com/geotechnical-instruments/inclinometers/ The Encardio-rite offers T-type thermocouple (Copper-Constantan) for the measurement of internal temperature in concrete structures. It consists of two dissimilar metals, joined together at one end. When the junction of the two metals is heated or cooled a voltage is produced that can be correlated back to the temperature.

21. 7 WHERE IS THE TEMPERATURE SENSOR USED? • • • • • • The temperature sensors are used for verifying design assumptions that will promote safer and economical design and construction. They are used to measure the temperature rise during the process of curing concrete. They can measure rock temperatures near liquid gas storage tanks and ground freezing operations. Temperature sensors can also measure water temperatures in reservoirs and boreholes. It can be used to interpret temperature related stress and volume changes in dams. They can also be used to study the temperature effect on other installed instruments.

22. 8 ADVANTAGES OF ENCARDIO RITE’S TEMPERATURE SENSOR • • • • • • • • The Encardio-Rite temperature sensor is precise, low cost, and extremely reliable. They are suitable for both surface mount and embedded applications. The low thermal mass results in faster response time. The vibrating wire temperature sensor is fully interchangeable; one indicator can read all sensors. It has a weather-proof body rated IP-68. They come with indicators that are readily available for direct temperature display. The temperature probes have excellent linearity and hysteresis. The vibrating wire technology assures long term stability, quick and easy readout.

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