How a Pt100 RTD Works

Also known as Platinum100, Pt100 resistance temperature detectors (RTDs) play a crucial role in myriads of process control installations. Repeatable and precise temperature measurement is a key requisite for many processes, such as chemical reactions, pasteurization, cooling and heating, etc.

If you’ve ever used a Pt100, you’ve probably wondered how it works. What is it made of? How does it work? How does it differ from a Pt1000?

In this post, we’ll answer all of these questions and more. We’ll introduce you to the Pt100 resistance temperature sensor and describe the physical properties that make it such a critical component of process control. Lastly, we’ll show you how to integrate Pt100 sensors into the control and measurement system.

So, if you’re interested in learning how a Pt100 works, read on.

What is the Pt100 Sensor, and How Does it Work?

A Pt100 temperature sensor falls in a category of sensors known as resistance temperature detectors (RTDs). RTDs are sensors that can change resistance if the temperature of the object where they’re inserted changes. The resistance change is relative to the temperature, and it differs linearly with temperature.

Generally, the resistance of the RTD rises when the temperature rises. For instance, the resistance of a Pt100 sensor is 100 ohms at 0⁰C and 138.5 ohms at 100⁰C. Therefore, the change in resistance is 0.385 ohms per degree Celsius change.

Therefore, if we can determine the resistance of an RTD, we can identify its temperature. We can derive temperature by determining resistance due to the physical properties of the resistance temperature detectors.

RTDs can be constructed from various metals, including copper and nickel. But platinum has certain physical properties that make it ideal for manufacturing RTD sensors. Let’s discuss these physical properties in detail.

What Are the Physical Properties of Platinum (Pt100)?

• Basic element. Platinum is a basic element, represented by the chemical symbol Pt. Its molecular weight is 195, making it a heavy metal with free-flowing electrons. These properties make platinum a great conductor of electricity – although not as great as silver or copper.
• Linear electrical resistance. Platinum displays an electrical resistance that linearly varies with temperature – its electrical resistance is 100.00ohms at 0⁰C. This property makes it perfect for manufacturing temperature sensors. Although platinum is a precious metal and tends to be quite costly, it offers the best stability and linearity of any material. It’s also very stable at excessive temperatures and resistant to chemical attacks and corrosion.
• Inert. Platinum is quite inert, making it highly valuable for temperature measurement. Being inert means that platinum cannot greatly react with other compounds. This property explains why platinum is also used in high-temperature thermocouples

Application of Pt100 Resistance Temperature Detector

Typically, a Pt100 is constructed by winding a platinum wire around the non-conductive core to support the wire. The whole assembly is enclosed in a sheath to keep the sensor safe and provide it with stability.

In industrial applications, RTDs are mainly encased in protective metal tubes known as thermowell. The instrument engineer determines the design of the thermowell and the length of the Pt100 RTD. Usually, RTDs are manufactured from one platinum wire, providing the sensor with two leads.

These leads are connected to an I/O card specially designed to support RTD inputs. Alternatively, they can be linked to the temperature transmitter to produce an output of 4-20 milliamp signal.

In both cases, the I/O card or temperature transmitter will be equipped with firmware that will denote the temperature from the measured resistance.

How a Pt100 RTD Works: The Bottom Line

In this post, we have introduced you to the Pt100 resistance temperature sensor, its key physical properties, and how they can be used in control systems and industrial measurements. We have also shed light on platinum’s linear relationship between resistance and temperature. These properties make Pt100 sensors accurate, affordable, and reliable for many areas requiring temperature measurement.

Therefore, when you come across the Pt100 sensor next time, you’ll have a clearer view of how the sensor functions.