One of the most common industrial processes is temperature sensing and measurement. Temperature is the most abundantly found physical property and hence is most widely measured across numerous industrial applications. Temperature sensors are available in a wide range of specifications. Two broad categories of temperature sensors are contact and non-contact temperature sensors. If the fluid or substance in question can be touched, then you need a contact sensor. If it cannot be touched then you need the non-contact sensor. Here we have discussed the features of both these types of sensor.

Features and application of contact temperature sensors

If satisfactory thermal contact is possible with the substance then contact temperature sensors would be the right choice. For contact temperature sensors the temperature range should be between – 40°C to 1700°C. The platinum thermocouples at 1700°C lose calibration almost instantly and the wires begin to sag and soften. For this, use type B platinum and rhenium thermocouples which are stable even at higher temperatures. If the temperature is as low as – 40°C then you may face cryogenic problems. Higher level contact sensors are capable of measuring temperatures below – 40°C. It must be remembered that a high degree of expertise is required for measuring extreme temperatures.

Features and application of non-contact temperature sensors

Non-contact temperature sensors are available in numerous types. Each one suits a different purpose. Some of the common types are optical pyrometers, IR pyrometers, radiation thermometers, radiation pyrometers and thermal imagers.

This type is used for measuring the temperature of objects in motion. Contact with a substance can greatly damage the sensor. The internal temperature of the sensor may change drastically and affect the final readings.

Temperature signal conditioners get DC and AC voltages as signal inputs from different types of sensors. These sensors might include thermocouples, resistance temperature detectors and thermistors. These offer current, frequency and voltage outputs to different devices like counters, timers, potentiometers and relays.

The temperature signal conditioning devices amplify, filter and convert these analogue inputs into digital signals. Devices that include transducers or integral sensors often provide current and voltage excitation.

Temperature signal conditioners often work with two, three or four-wired RTDs made from different metals. These metals also feature a range of reference resistances. Temperature signal conditioners can also receive signal inputs from thermocouples that come integrated with or without cold junction thermocouples.

Some different specifications to consider

If you are buying temperature signal conditioners you must consider the number of differential and analogue channels that the device features. If single-sided outputs are available, most suppliers specify about the maximum number of analogue output channels as double the number of differential outputs available.

Differential channels with two inputs are always defined as the voltage signal between two different inputs. Sampling frequency, filtering and accuracy are some other specifications of temperature signal conditioners to look for. Depending on factors like signal conditioning hysteresis, temperature and linearity, accuracy is mostly defined as a fraction of the full measurement range.

The best feature of signal conditioners with integral filters is the fact that they allow some frequencies to pass through while other are attenuated. Printed circuit boards (PCBs), integrated circuits (ICs) and standard DIN rails are some form factors available for temperature signal conditioners.

Temperature sensing is one of the most common industrial processes. There are many different types of temperature sensors in varied specifications, ranges and prices available.

This guide will empower you with some knowledge on how to choose the right temperature sensor. The two main types we will discuss here are contact and non-contact temperature sensors. Your choice of sensor will depend on whether you can touch the fluid or object in question or not.

When should you go for a contact temperature sensor?

A contact temperature sensor should be used if you can make satisfactory thermal contact with the liquid. The temperature range should be between – 40°C and 1700°C, although the two temperature limits are subjective. Platinum thermocouples will lose calibration quickly at 1700°C and the attached wires will become softer, whilst Type B platinum and rhenium-tungsten thermocouples are stable even at higher temperatures.

You need to have a certain degree of expertise at high temperature measurements. Generally when temperatures are closer to – 40°C, cryogenic issues may arise. Some contact sensors are capable of temperature measurement at temperatures below that also.

When should you go for a non-contact temperature sensor?

Non-contact temperature sensors are available in many versions. A few versions are radiation thermometers, radiation pyrometers, IR pyrometers, optical pyrometers and thermal imagers.

To put it simply, a non-contact temperature sensor should be used for moving objects. Contact will damage the sensor and change its own temperature greatly. This type of sensor is apt for measuring temperatures of large surfaces. A non-contact temperature sensor can also be used to measure the temperatures of distant objects and bodies.

As an essential part of most industrial operations, temperature measurement is usually accomplished with the help of a temperature sensor.

When selecting temperature sensors, there are many considerations that have to be made according to the application of the device. Mentioned below are two types of temperature sensors that are used in many applications.

RTD- These temperature sensors are commonly made from copper, platinum and nickel. The basis of their operation relies on the increase in resistivity which takes place when the temperature of the material increases. Generally, RTDs are constructed using basic techniques that include connecting a sensing element to a non-conducting element made from mica, glass or ceramic. The element is capable of measuring the resistance and the temperature is obtained from this result.

Thermocouples- These differ from RTDs in terms of structure as they consist of two metals, joined at one end. This produces a voltage which can be converted to a temperature reading depending on the temperature the metals come into contact with. The physical ranges of temperature sensors are quite large as extension wire can be connected to the sensing junction (the meeting point of both metals). Thermocouples are more affordable than RTDs; however they may produce imprecise results if there are other components in the electric circuit.

Understanding which type of temperature sensor suits your application best can help to make your process control application run smoothly.

Temperature controllers accept inputs from the thermometers or temperature sensors and offer output to a control switch. They are used in many different control techniques. Similarly, limit controllers create set points that send a signal to start or stop a process variable when it reaches a predefined set point.

Linear controllers are equivalent to the variable input signal. The PID or proportional, integral and derivative control needs real-time system feedback. These PID controllers monitor the error between the actual value and desired variable value and regulate the control accordingly.

Fuzzy logic is a control method wherein the variables have imprecise values (partial truth) instead of a binary status (completely false or completely true). Temperature controllers use non-linear or advanced controls such as adaptive gain, neural networking and emerging algorithm are also available.

Specifications of temperature controllers

Some crucial specifications of temperature controllers include number of outputs, inputs, number of zones, output types and input types. The number of outputs is the addition of all outputs used for compensating, correcting or controlling the process. Similarly, the number of inputs is the sum of signals that are sent to temperature controllers.

The output types of temperature controllers include current loops, analogue voltage, relay or switch outputs, and frequency or pulses. On the other hand, input types of temperature controllers include current loops, analogue signals, direct current (DC) voltage from potentiometers or resistors, relay or switch inputs and frequency inputs.

While looking for temperature controllers, you should consider the above specifications and application for selecting the best one.

Temperature sensors are used to monitor and control the temperature of your company’s equipment. The primary function of these devices is to trigger an alarm and inform the operator of the rising temperature in the equipment. Special heat-resistant materials are used to manufacture these sensors.

There are many different kinds of pressure sensors available on the market. Outlined below are the two basic types of temperature sensors.

Non-contact pressure sensors

These devices are commonly used in a wide range of different industries. A distinct feature of non-contact temperature sensors is that they can read the temperature of a device without actually having to come into contact with it. They use infrared energy to monitor the temperature of the equipment. Non-contact temperature sensors can also be used to monitor the temperature of different kinds of metals, plastic, ceramic and semi conductors.

Contact temperature sensors

These temperature sensors are more accurate than non-contact sensors, as they come in direct contact with the device that needs to be monitored. There is no heat flow between the units and the sensors; however, you have to make sure that the surface used for monitoring the temperature is stable.

They are cost efficient and do not need regular maintenance due to the lack of movable parts. They are highly versatile in nature and can be subject to harsh conditions as the sensors have built-in strong steel covers and cooling jackets.

Temperature sensors are devices commonly used by industries to protect their expensive equipment from damage due to overload. With different kinds of equipment being manufactured on a regular basis, it has become mandatory for businesses to have temperature sensors installed.

Some temperature sensors work by making contact with the device to be monitored, while other sensors use infrared energy and work wirelessly to monitor temperature.

Temperature sensors are classified into two basic types – thermocouples and resistant temperature sensors.

Thermocouples

Thermocouples make use of two metals that are connected at one end to monitor the current generated, which in turn is used to register the temperature of the device. The point at which the two metals meet is called the sensing junction.

Infrared sensors

These are commonly used in industries and preferred over other types of pressure sensors as they use a no-contact mechanism for monitoring the temperature of certain devices. Infrared energy is used by these sensors. The cost incurred by the company on the maintenance of these temperature sensors is almost negligible due to the lack of any wires or moving parts within the device.

Resistance Temperature Detectors (RTD)

Resistance Temperature Detectors (RTDs) use the resistor that changes the resistance value when there is a change in the temperature of the device being monitored. They are commonly used in laboratories and industries. They have gained a good reputation for their accuracy, repeatability and stability.

Industries have started to realise the importance of temperature sensors in protecting equipment. The use of these devices ensures that the equipment remains in a functional condition for as long as possible.

There are a number of industries that depend on temperature indicators to ensure the good quality of their end product. Platinum Resistance Temperature Detectors (RTDs), thermistors and thermocouples are some of the best sensors available for measuring temperature rates.

Different features of temperature sensors

Platinum RTDs

Platinum RTDs operate on a simple principle, wherein the changes in electrical resistance of certain metals can be calculated depending on the rise or drop in temperature levels. While RTDs can be constructed from a range of different metals, platinum is most commonly used due to its increased resistance to temperatures. Furthermore, RTDs are easy to recalibrate, offering a stable output over a longer period of time.

Thermocouples

Thermocouples are arguably one of the most popular and easiest indicators used today. The temperature measurement range of thermocouples ranges from -300 Fahrenheit to 2300 Fahrenheit.

Thermocouples function using a connection of two different metals that create different voltage levels according to the temperature level. They are affordable and highly user-friendly instruments. They are well known for their fast response times and are also able to withstand high levels of use.

Thermistors

Similar to thermocouples, thermistors are also adaptable, affordable and easy to use. They are mostly used for simple temperature readings.

As each of the above indicators are regarded as quality instruments for measuring temperature rates, it is up to you to decide the one that best suits your application needs.

Temperature indicators and temperature instruments are designed for analysing and monitoring temperature. They are either equipped with an integral sensor or need a sensor input. Nearly 16% of the process instrumentation currently available measures, controls or indicates temperature readings.

In most industrial applications, it is essential to monitor temperatures due to the manufacturing needs. This data can also be used to offer historical data that can be used for finding out problems in a control system. Data collection in industry can vary from the sophisticated DCS (Distributed Control Systems) for both control and logging data to simple manual systems using portable indicators.

Temperature measuring instruments

Affordable portable temperature indicators do not offer any memory or recording features. The readings from these portable temperature indicators and instruments need to be recorded by hand. Some portable indicators can however come with a small amount of memory so that measurements can be collected and later on downloaded to a personal computer.

A chart recorder is also another device that is used for recording temperature data. Usually, these recorders offer a digital indication and digital readouts of the process temperature of the scanned or selected points.

Distributed control systems are also available that provide data-logging as a part of their measuring capabilities. As these systems are computer based, the data-logging function is programmable to nearly any configuration. If you are looking for temperature instruments and indicators you must consider some general specifications such as input options, the sensed temperature range and the number of channels or inputs.

Similar to pressure switches and transducers, temperature sensors are also used extensively in utility and manufacturing plants today. The main function of these sensors is to check the temperature levels of different applications. After installing these sensors you can check when temperature levels fall below acceptable levels.

To fulfil various industrial needs, two different types of temperature sensors are used. The following is some information about the two most popular kinds of temperature sensor:

Contact temperature sensors

These temperature sensors are commonly used in many industries and manufacturing plants because they are so affordable. If you are buying them then you must know that contact sensors must be kept in contact with the specific application to monitor the temperature. Contact temperature sensors can only be used in applications which have stable surfaces.

Non-contact temperature sensors

As the name of these sensors suggests, they can read the temperature of different applications from a far away distance. This means that you do not have to keep non-contact sensors near the application to monitor temperature levels. Temperature reading is thus possible using infrared energy to check temperature levels.

Consider the maximum temperature sensing limits and then buy a sensor to suit your requirements.