Temperature sensors are nothing but measurement instruments that ascertain the exact temperature by sensing certain physical characteristics. These may include electromagnetic fields, thermal radiation or electrical resistance.

The main types of temperature sensors explained

There are different temperature sensors available on the market. Examples of some are bimetal switches, liquid level sensor and thermistors. Thermocouples contain two wires made of different metal each. These wires are soldered to a junction, which is left exposed on the measurement instrument. The other end of the wire is connected to a reference junction. Thermocouples are available in four varieties. There are companies who have Constantan, Chromel and Alumel as trademarks.

Resistance temperature sensors are used to detect changes in temperature. They convert elements into current signals using a thin-film serpentine. Thermistors are very sensitive but have a confined range of temperature. The two main types of thermistors are positive temperature coefficient and negative temperature coefficient. There are other temperature sensors that are available with alarms. Temperature sensors are also available in digital and analogue properties.

Application of temperature sensors

Temperature sensors are used in varied industries. They are commonly used in chemical labs, the manufacturing sector, hospitals, in air conditioning units as well as in alarm systems. They are very important in gauging the correct temperature reading.

Temperature sensors are also used in airplanes and in vehicles to gauge engine temperatures. These sensors help detect overheating of machines. In hospitals doctors use temperature sensors to keep record of a person’s body temperature. Households use temperature sensors to set the room temperature accordingly.

There are many different types of temperature sensor. Be it as basic as a thermometer or highly developed as electrical heat recorders, these temperature sensors are used for a variety of industrial purposes.

The more superior form of contact measuring is known as resistance temperature detectors (RTDs) and thermocouples. The temperatures are typically measured in liquids or through physical contact with the target’s surface.

The functioning of a resistance temperature detector

Contact measurements are not always required and there are other alternate ways to measure heat. There are new temperature sensors in the market that can measure heat without any physical contact. Normally this feat can be established with the use of air ionisation or infra-red technology.

When selecting a sensor you will have to consider a number of possibilities that can make it difficult to make a decision. An important aspect of this process is the temperature range that has to be measured. This depends on the accuracy levels offered by your device and the time taken by it to show you results. For those who want an accurate reading, an RTD sensor will serve their purpose.

Thermocouples, on the other hand, are an affordable and cost effective option.

The RTD uses the increased resistance caused by heat to give us an accurate measurement of the object’s temperature. RTDs are made of metals such as copper, nickel and platinum. The chemical property of the metal is of crucial importance in the selection process. Nickel and copper are used to measure low temperatures, whereas platinum is used to measure extreme temperatures.

As you are now familiar with the temperature sensors, this will help you choose the right type of sensor for your needs.

Temperature sensors are devices that capture complex data related to temperature. These are later converted into simple forms which can be understood by certain devices.

Where temperature sensors are used

Temperature sensors are generally used in science and biological laboratories. They are also used in houses, offices, aircrafts and other places to project temperature levels. Temperature sensors are very accurate. They can pin point the exact temperature within a room or the atmosphere. Scientists use it to gauge chemical reactions, doctors use them to take body temperatures and households use them to regulate room temperature. Pilots also use temperature sensors to gauge altitude while manoeuvring aircraft.

The types of temperature sensor available

Infrared temperature sensors are used to measure the energy given off by two objects. They are used in infrared thermometers. Infrared sensors were first developed in the 19th century and are used in security systems and fire alarms. Analog temperature sensors are important. They are used in the automobile industry to detect motor temperature, battery health and to estimate accurate data. The main features of analog temperature sensors are humidity detectors and digital control panels.

Wireless temperature sensors are available in a variety of versions. They are easily available and come with different features and functions. Wireless temperature sensors have two main components; the remote sensor and the wireless outdoor thermometer. High temperature sensors are another kind available. These are generally used in college and school science laboratories. High temperature sensors are also used in air conditioners and heat control systems.

There are a variety of industries that use temperature sensors in daily procedures. There are two basic types of temperature sensor. They are known as thermocouples and resistance temperature detectors- commonly referred to as RTDs. Temperature sensors are used for the measurement of temperatures of liquids, gases, large surfaces and many substances. Contact is not compulsory as some temperature sensors can operate without touching the substance or object in question.

Non-contact temperature sensors get a reading by measuring the air around the target object. The heat of an object causes the ionization of air. The non-contact temperature sensor measures temperatures from a distance by checking the level of ionization.

Features of RTDs

When accurate results are necessary, opt for RTD sensors. They might be slightly expensive than thermocouples but resistance temperature detectors help to make crucial decisions by minimising risk factors arising out of low accuracy. Resistance temperature detectors depend on the resistance caused due to the increase in temperature of a substance. RTD sensors are manufactured from substances such as platinum, copper and nickel. Thermocouples are cheaper, affordable and can be used for a variety of different purposes.

Features of a thermocouple

Thermocouples are different as they use two different metals for temperature sensing. These metals are joined at one end and help a thermocouple to generate a voltage. This voltage can be converted to a temperature reading. The spot where these two metals meet is known as a sensing junction. This junction can be attached with more wires to increase the physical range of a thermocouple.

The selection of a temperature sensor depends on its use, application and specifications. Once you have clearly understood the needs of your process, you will be in a better position to make the right choice.

Temperature sensors are devices that are used to monitor temperature changes. Temperature sensors are also used in thermometers to gauge the temperature. There are different types of temperature sensors. Some common types are explained below.

Resistive temperature devices

Resistive temperature devices are a type of temperature sensors in which the resistance increases as the temperature rises. The increase in temperature can be expressed in relation to degrees. Resistive temperature devices can measure temperatures ranging between 400 degrees F and 1200 degrees F. They give accurate measurements. RTDs are used in a number of industrial applications as they can effectively measure fluid and surface temperatures.

Thermistors

Thermistors are designed in a way that the semiconductor inside the device fluctuates with every change in temperature. As the temperature increases, the resistance decreases and this can be expressed in degrees. These temperature sensors are used in a wide number of household appliances that get affected with any change in temperature. Thermistors are sensitive compared to other temperature sensors. For recording any temperature changes, they have a medium to fast response time.

LM35 temperature sensors

These temperature sensors are more precise compared to thermistors. The voltage does not have to be boosted as these temperature sensors use a higher voltage. It is designed in way to be included in an incorporated circuit on a circuit board. The voltage measured by this device can be expressed in Celsius temperature. It does not require any adjustments to give accurate readings. A good thing about LM 35 temperature sensors is that it works with minimum power so the device does not heat up. When it is included in circuits, it can give rise to many events like activating a relay when the device reaches a certain temperature.

Temperature sensing technology is widely used in industrial processes. There are two different versions of contact sensors for this purpose. They are known as thermocouples and resistance temperature detectors or commonly referred to as RTDs. There is also another type called a non-contact temperature sensor. These measure temperatures of substances and surfaces which are too hot to be touched by contact temperature sensors.

Usually contact temperature sensors are used for liquids and large surfaces. Here we have discussed some important considerations that need to be made while selecting a temperature sensor.

Selection of a temperature sensor – vital considerations

You must consider many vital aspects before selecting a particular temperature sensor. You must first check the range of temperature it can measure. Other crucial aspects are accuracy levels and response time. The reason you need to consider accuracy and response time is because these measurements will vary with differences in methods of measurement. If accuracy is what you are looking for then an RTD sensor is the best option. It may be a slightly expensive option but if you are looking for a cheaper contact sensor alternative then you should go for a thermocouple.

RTD temperature sensors are made of platinum, copper or nickel. RTD sensors have a non-conducting material such as glass or mica which is connected to the sensing metal. Resistance from the non-conducting material is measured and displayed as a reading.

Thermocouples are made of two different metals which join to produce a voltage which can be converted into a temperature reading.

Thermocouple temperature transmitters are temperature sensing devices. They are widely used for transforming small milli-volt (mV) output into a current signal (usually 4-20mACD). The current signal received from thermocouple temperature transmitters is resistant to noise and voltage drops over a long distance.

Thermocouple temperature sensors are used with bimetallic devices such as thermocouple temperature probes. They can be used for a number of temperature sensing applications. Isolated thermocouple temperature transmitters greatly help to eliminate ground loop problems. This is made possible by separating the input of the transmitter from its output.

Output options for thermocouple temperature transmitters include analogue current, analogue voltage and relay/switch output. While choosing thermocouple temperature sensors, gauge is a crucial consideration factor.

Types and functioning of thermocouple gauge

Thermocouple gauge corresponds to the small diameter of thermocouple wire used. Some thermocouple temperature probes also come with multiple or optional gauges. Different styles of thermocouples include:

Flexible thermocouples – These are thermocouple elements that utse a flexible sheathing or section(s).

1-hole full-length thermocouples – They are insulators that offer insulation to each wire.

2-hole full-length thermocouples – These insulators are used to position both wires in a single insulator.

Bare wire thermocouples – These devices consist of a bare wire element devoid of any protective insulation.

Performance specifications of thermocouple temperature probes

When you are looking to purchase thermocouple temperature probes or transmitters, it is important to consider their performance specifications. These include analogue voltage, resistance, temperature and analogue current. Thermocouple temperature probes are devices that receive analogue voltage input in the range of 0-10 VCD. Other devices receive analogue current inputs in the range 4-20mA.

Temperature indicators and instruments are specially designed for temperature monitoring and analysis. They either come equipped with a sensor or need a sensor input.

In most industrial applications, collecting temperatures as a permanent record for manufacturing needs is important. These devices provide historical data which can be used to find out problems within a system. These data collection methods vary from using simple, inexpensive and portable indicators to more sophisticated DCS (Distribution Control Systems) that can both log and control data.

The most cost-effective and portable indicators do not offer any kind of memory or recording features. Readings from these portable temperature indicators and instruments are required to be recorded by hand. On the other hand, some portable indicators do come with memory. This allows users to store the data in the memory and then download it onto a computer.

Other devices used for temperature measurement

Chart recorders are other devices used for recording temperature data. These recorders provide digital readouts. They also offer a digital indication of a process temperature at scanned and selected points. The DCS also provides a data-logging feature as a part of its operating capability. As these systems are mostly computer based, data-logging functions can be programmed to any required configuration.

When looking for temperature instruments and indicators, input options, sensed temperature range and number of channels or inputs are some important points to consider. Input options include permanent probe or sensor, RTD inputs, thermocouple inputs, solid-state inputs and thermistor inputs.