Temperature Sensors in Control Systems

Temperature Sensors: Definition, Types, and Applications

Temperature sensors are crucial in modern industrial processes. They enable accurate monitoring and control of thermal conditions. These sensors play a critical role in automation to maintain the optimum temperature. they ensure safety, maximum performance, and efficiency. They contribute significantly to system optimization and operational reliability.

Temperature sensors are the basis for data acquisition in advanced control systems. They deliver real-time temperature readings to controllers such as Programmable Logic Controllers (PLCs), which support regulated processes and ensure operating stability.

In the cement, steel, oil, and gas Industries, temperature sensors work together with pressure and level sensors and modern automation systems to provide extensive monitoring solutions. This integration supports downtime reduction, improves system performance, and ensures process stability.

Temperature sensors are situated at the field level of the automation pyramid, where measured data is collected. Field-level data is transmitted to higher automation layers, such as supervisory control and data acquisition (SCADA) systems. This data is processed for analysis and decision-making. It is also critical in compliance with safety standards, energy management, consumer applications, and industrial automation.

One of the key factors, where temperature sensors play a substantial impact is renewable energy. In solar power systems, temperature sensors monitor the solar modules’ temperature to optimize energy conversion efficiency and improve the thermal response of the overhaul system.

Temperature sensors are also used in wind energy systems to regulate the temperature of gearboxes and generators, preventing overheating and equipment failure. Additionally, temperature sensors help control the runaway of lithium-ion batteries' behavior and ensure the energy storage systems' efficiency and safety.

By integrating temperature sensors with PLC and automation systems, industries can be improved and have control and exceptional optimization of energy consumption and cost reduction. These approaches maximize productivity, increase product quality, and make the overhaul process more intelligent and efficient.

Temperature sensor

In this article, we will explore the role of the temperature sensor in modern control systems and why we need it. We will also explore its history, explain the types of temperature sensors, and how to test them. We will discuss the impact of temperature sensors on renewable energy sources.

What are the definition of temperature sensors?

A temperature sensor is a device used to convert the temperature to an electrical signal. It can be found anywhere, including in the fridge, irons, ovens, heaters, and air conditioners. Temperature sensors are also used in cars to control the temperature of engines and protect them from overheating.

What is the history of temperature measurement?

Measuring the temperature started about 400 years BD by using the human hand to decide whether a person has a fever or not. That measurement developed through the invention of the thermoscope and the glass thermometer (which is used till now). The main difficulties of these old devices are the accuracy and the standardization of the scales (start and end points).

Modern techniques for temperature measurement were developed over time. In 1821 when the Seebeck effect was discovered by a German physicist called Seebeck. The Seebeck effect says that when 2 metals are connected at their ends, there will be a changing of volts across the far away terminals when the temperature changes.

This was the basis for building the most popular temperature sensor devices called thermocouples. There are two main types of sensing criteria as mentioned in the sensor article, digital and analog. We will discuss in detail the various examples and temperature measurement types.

What are the types of temperature sensors?

Temperature sensors have many types. these types depend on the application that uses this specific type of temperature sensor. these types could be classified as:

Thermostat or temperature switch:

One of the main types of digital temperature sensors is the temperature switch or thermostat. it depends on the effect of the temperature on a material like copper. the temperature changes the physical properties such as length to work as an on-off switch to start/stop devices like a heater in the iron, fans in your car, and the A/C of cars and homes.

Normally this thermostat could be adjusted manually by increasing or decreasing the gap between the 2 contacts of sensors to allow more or less temperature to let the sensor change its state causing the device to run or stop. Normally the temperature switch or thermostat is equipped with a safe margin of temperature to protect the contacts from damage due to the fast and rapid change in temperature.

Thermostat (temperature sensor)

Temperature gauge.

The temperature gauge's operation is the same as the temperature switch. The difference is that the temperature gauge contains a pointer slides on a flat or round scale. F and C indicate the temperature unit. This sensor can’t be used in the temperature control circuits because it is not accurate, has no electrical connection, and depends on the visual follow-up of the temperature.

Temperature gauge

Resistance Temperature Detectors RTDs,

Another type of temperature sensor is the Resistance Temperature Detectors RTD. In this sensor, the resistivity changes according to temperature changes this is called the temperature coefficient (TC). These materials could be copper, platinum, and nickel. When the temperature changed the resistance changed based on the temperature coefficient.

Resistance Temperature Detectors

The Positive Temperature Coefficient (PTC) means that the resistance increases when the temperature increases. The Negative Temperature Coefficient (NTC) means that the resistance decreases when the temperature decreases as shown in the next picture.

PTC and NTC temperature sensors

What are the PT100 and PT1000?

PT100 and PT1000 are temperature sensors that change their resistance with the change of temperature (same as the RTDs) but, the difference is that there is a resistance reference values which are (100 Ω and 1000 Ω respectively at 0 o C).

PT 100 sensor

How do we check the RTDs and thermocouples?

Checking the functionality of the resistance temperature sensor is done by using the digital multimeter to determine the value of Ω of the device. increase the temperature and record the measured value of the resistance. There are standard tables for each product of the resistance temperature sensors.

The measured values are compared with the values in this table to confirm the accurate performance of the device. In industrial processes where the working and operation temperature is normally higher than other applications (sometimes exceeding 1500 o C), the temperature needs a temperature controller to monitor and control the temperature. 

In heavy industries such as cement, glass, and steel, there is a special device called thermocouples. These thermocouple devices. It works based on the seebeck effect explained at the start of this article. The output of these thermocouples is mV changes when the changing in temperature. 

These thermocouples are described as special two metals connected together at the end forming the junction. When this junction is heated, the voltage difference in mV is changed also and it can appear at the other terminals of the thermocouple.

The electrical signal that comes from the thermocouple could be used directly as a feedback signal in the control system to control or monitor temperature processes by comparing it with a predefined temperature set point.

In summary, because of the importance of temperature, we have to measure, monitor, and control it. We explored the main role of temperature sensors in controlling and optimizing any industrial processes. we discussed also the history of temperature measurement started in 400 BC and has been developed to reach the current situation.

There are many types of temperature measurements such as temperature switches, temperature gauges, Resistance temperature detectors (RTDs), and Thermocouples. In the coming article, we will complete other temperature measurement techniques and applications