So-called bare wire thermocouples expose the thermocouple wire directly at the probe, which provides rapid response times for the device but also increases the risk of corrosion and device degradation resulting from the exposed junction. An uncommon ungrounded thermocouple is one in which a dual thermocouple arrangement is used with the sheath isolated from the thermocouple wires and each thermocouple is isolated from the other as well. For more on these sensors, check out our guide on types of thermocouples.
Resistance Temperature Detectors , abbreviated RTDs, are temperature sensors that make use of the change in the electrical resistance that occurs in a conductive material to establish a value for the temperature. Conductors of electricity, such as metal, exhibit electrical resistance that is a measure of the relative ease with which electrical current will flow through the conductor when a given voltage or potential difference is applied.
As the temperature changes, the electrical resistance, which is measured in Ohms, also changes, with higher temperatures resulting in an increase in resistance. RTDs consist of a resistive element through which a small electrical current is passed, typically in the range of milliamps, and the resistance is measured.
Any temperature changes will alter the value of the resistance measured, which can be equated to a temperature value by knowing the properties of the materials used for the resistive element. Platinum is a metal of choice used in RTDs owing to the fact that it is highly stable, is chemically inert, can function over a large range of temperature, and exhibits a very strong linear relationship between its resistance and temperature.
This last characteristic simplifies the process of converting electrical resistance into temperature readings. The material used in RTDs is specified by their temperature coefficient of resistance TCR , which is a measure of how the electrical resistance of the material changes with respect to a one-degree change in temperature.
Metals and electrically conductive materials exhibit a positive value of TCR, while semiconductors and non-metallic substances would exhibit a negative TCR, meaning that they become less resistive with increases in temperature. RTDs are built typically constructed as either thin-film or wire wound type. Film type RTDs use platinum that is plated onto a ceramic plate which is encapsulated in glass, while wire-wound RTDs use platinum wire wound around a ceramic core and sealed with glass encapsulant.
Different sensor wiring configurations are used with RTDs, generally 2-wire, 3-wire, or 4-wire. Using 2 wires provides a simple arrangement but suffers from accuracy given that the resistance of the wire leads cannot be isolated from the measured resistance value. The 3-wire configuration allows for two separate measurements to be made, allowing the impact of the wire lead resistance to be subtracted out from the total resistance measurement, providing a net resistance value. The 4-wire configuration allows for direct measurement of the sensor resistance to be made, excluding the impact of the lead wires.
A Wheatstone bridge arrangement is typically used to perform the resistance measurements associated with RTDs to establish temperature values. Thermistors , a term derived from a concatenation of the words THERM ally sensitive res ISTORS , are temperature sensing devices that make use of the property of the change in electrical resistance that occurs with temperature as a means of providing a reading for the temperature value. These passive devices exhibit a precise change in their electrical resistance that is proportional to the changes in temperature of the device.
Negative Temperature Coefficient NTC thermistors are ones whose resistance decreases with an increase in temperature, while Positive Temperature Coefficient PTC thermistors exhibit an increase in electrical resistance with increasing temperature.
The NTC thermistor is most frequently used in temperature sensing applications, while the PTC thermistor has uses in electrical circuit protection applications such as limiting the inrush current or surge protection for a circuit or device.
Thermistors are available in a wide variety of materials, packages, and forms including disk, chip , bead, or rod depending on the need for operating temperature range and response time. They can be packaged or encapsulated in epoxy resin, glass, baked-on phenolic, or painted. Generally, they are small, low cost temperature sensors that offer fast response times over a limited operating temperature range. They also have a larger change in resistance value per unit change in temperature, therefore offering a potential for more sensitivity and accuracy in readings.
Limitations of thermistors are that they feature non-linear temperature response curves, unlike RTDs, and are subject to self-heating if the excitation currents are too high. Accurate measurements are vital in ensuring the success of these processes. There are many applications that are not-so-obvious, which use temperature sensors. Melting chocolate, using a blast furnace, controlling a hot air balloon, freezing substances in a lab, running a motor vehicle, and firing a kiln.
Temperature sensors come in different forms, which are used for different methods of temperature management. There are two categories of temperature sensors which are contact and non-contact. Contact sensors are used mainly in hazardous areas.
The below are contact temperature sensors:. The metal can be made of different materials including platinum, nickel, or copper. However, platinum is the most accurate and therefore carries a higher cost. The Thermocouple is a sensor made up of two wires with two different metals connected at two points.
The voltage between the two wires reflects the change in temperature. An RTD is the most accurate temperature sensor. The platinum RTD has very good accuracy, linearity, stability and repeatability as compared to thermocouples or thermistors. A thermocouple is a type of temperature sensor which is used to measure the internal temperature of an object. If all the wires and the thermocouple are made of the same material, temperature changes in the wiring do not affect the output voltage.
Hence, wires made up of distinct materials are needed. The sum of all the thermoelectric forces in a circuit with a number of dissimilar materials at a uniform temperature is zero.
This implies that if a third material is added at the same temperature, no net voltage is generated by the new material. At Encardio-Rite, we have specialised temperature testing chambers with already known temperature and temperature control systems to test the accuracy and quality of our temperature sensors.
This was all about the temperature sensors, their different types, applications, uses, as well as, working principle. Do let us know your queries in the comments section below. You must have heard about this term many times. Be it with the issue of groundwater scarcity or around the topic of groundwater seepage. When it comes to road and bridges safety, Pennsylvania has always been quick and alert.
Having come into existence from the earliest of human civilizations, tunnels have long been a part of mankind. However, things have changed drastically, when it. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. What are the temperature sensors? What do temperature sensors do? What is a temperature sensor used for? What are the functions of a temperature sensor?
How does temperature sensor work? 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. The contact and non-contact temperature sensors are further divided into: Thermostats 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.
Thermistors Thermistors or thermally sensitive resistors are the ones that change their physical appearance when subjected to change in the temperature.
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. Thermocouples One of the most common temperature sensors includes thermocouples because of their wide temperature operating range, reliability, accuracy, simplicity, and sensitivity.
On being subjected to temperature, a voltage drop is developed across the junction. Negative Temperature Coefficient NTC Thermistor A thermistor is basically a sensitive temperature sensor that reacts precisely to even the minute temperature changes. Semiconductor-Based Sensors A semiconductor-based temperature sensor works with dual integrated circuits ICs. 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. 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 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. They are suitable for remote reading, scanning as well as data logging. Frequently Asked Questions What is the difference between the temperature sensor and temperature transmitter? What is a thermocouple? There are three laws for thermocouples as stated below: Law of homogenous material If all the wires and the thermocouple are made of the same material, temperature changes in the wiring do not affect the output voltage.
Law of intermediate materials The sum of all the thermoelectric forces in a circuit with a number of dissimilar materials at a uniform temperature is zero. Related posts. Tags: encardio , geotechnical instrumentation , sensors , Temperature Sensor.
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