The Pt100 sensor is present in virtually all industries that depend on thermal control, from food production to... petrochemistrySo, what exactly is a Pt100 and why has it become a benchmark when it comes to accurately measuring temperature?
What is a Pt100 sensor and what does the name mean?
The Pt100 is a RTD type temperature sensorThe acronym stands for "Resistance Temperature Detector." This means that it measures temperature based on the variation in the electrical resistance of a material.
The name is not random: “Pt” is the chemical symbol for platinum, the metal used as a sensor. The number “100” indicates that this sensor has a resistance of 100 ohms at 0 °C. In practice, this standardization facilitates identification and use in industrial systems. By looking at the abbreviation, the engineer already knows exactly the expected behavior of that sensor.
Unlike sensors made of nickel (Ni) or copper (Cu), platinum offers a more linear and repeatable response over a much wider temperature range, being able to operate from -200°C up to about 850°C in special constructions.
How does the Pt100 measure temperature in everyday use?
The operation of the Pt100 is based on the principle of electrical resistivity of metalsAll conductive metals share a common physical characteristic: their resistance to the passage of electric current increases as the temperature rises.
In practice, when the temperature of the medium increases, the thermal energy causes the platinum atoms to vibrate more intensely, which hinders the flow of electrons. For the Pt-100 RTD, this variation is quantified by... temperature coefficient (Alpha).
For standard platinum, according to IEC 60751, the coefficient is 0,00385 Ω/Ω/°C. This means that for every 1°C increase in temperature, the sensor's resistance rises approximately 0,385 Ω. The relationship between resistance and temperature is described by mathematical formulas that allow the controller to translate Ohms into degrees Celsius with high fidelity. For the range above 0°C, the following simplified formula, known as the Callendar-Van Dusen equation, is used:
Rt = R0 * (1 + A * t + B * t²)
Where:
- Rt: It is the resistance at temperature t;
- R0: It is the resistance at 0°C (which in the Pt100 is 100 Ω);
- A and B: These are constants defined by the technical standard.
Therefore, mathematical predictability is what makes the Pt100 the preferred sensor for industrial automation, ensuring that the signal read by the panel corresponds exactly to the thermal reality of the process.
Why is platinum used in this type of sensor?
The choice of platinum is not only related to tradition, but also to performance. The metal presents a combination difficult to find in other materials: chemical stability, corrosion resistance, and highly predictable electrical behavior. In other words, it responds to temperature without "surprises".
Furthermore, platinum is virtually non-reactive with the environment, which reduces the risk of distorted measurements over time. In industrial processes, where small variations can have large impacts, this characteristic makes a difference.
How is a Pt100 sensor constructed?
Despite the sophisticated result, the sensor's structure is relatively simple. It consists of a very thin platinum wire, wound or placed on an insulating support. This assembly is protected by a metallic sheath, which ensures mechanical resistance and protection against the environment.
In industry, the sensor is usually installed in a protective enclosure, known as a thermowell. This allows for maintenance without interrupting the process.
Why are there versions with 2, 3, and 4 wires?
A critical point in installing a Pt100 is the resistance of the copper cables connecting the sensor to the reading instrument. Since the sensor operates by measuring small variations in Ohms, the resistance of the conductor wire itself can generate reading errors.
Two-wire connection: This is the simplest, but least precise. The resistance of the cables is added to the resistance of the sensor, resulting in a temperature reading higher than the actual temperature. It is only recommended for short distances.
3-wire connection: This is the most widely used standard in the industry. The third wire is used to measure line resistance and automatically compensate for it in the controller. It offers an excellent balance between cost and accuracy for long distances.
4-wire connection: used in laboratory applications and ultra-high precision processes. It completely eliminates the effect of cable resistance, ensuring that only the variation of the sensor element is considered.
What is the difference between a Pt100 and a thermocouple?
When choosing the ideal temperature sensor for an industrial process, the decision between a Pt100 and a... thermocouple It depends directly on the necessary balance between precision, thermal range, and mechanical robustness. Although both fulfill the role of converting heat into an electrical signal, they operate under distinct physical principles that dictate their limitations.
The Pt100, being a resistance temperature detector (RTD), is based on the variation of the electrical resistance of platinum. Its great advantage lies in its long-term stability and very high repeatability. In processes where accuracy is non-negotiable, such as in the pharmaceutical industry or in chemical laboratories, the Pt100 makes more sense because it presents a much smaller reading error and does not suffer from the thermal "drift" so common in other sensors.
See the comparison:
| Criterion | Pt100 (RTD) | Thermocouple |
| Precision | High | Moderate |
| Stability | Excellent in the long term. | It suffers deviations over time. |
| Thermal Range | -200°C to 420°C (on average) | Up to 1800°C (Types S/R/B) |
| Robustness | Sensitive to strong vibrations | Highly robust |
| Cost | Superior | Lower |
Which one to choose, Pt100 or Pt1000?
The difference between Pt100 and Pt1000 sensors begins with the most basic and important piece of data: the electrical resistance at 0 °C, which is already indicated in each sensor's name. The Pt100 has 100 ohms at this temperature, while the Pt1000 reaches 1000 ohms. This may seem like just a numerical variation, but in practice, it completely changes the signal's behavior and how it is read by control systems.
In routine measurement, this difference translates into sensitivity. Because the Pt1000 operates with ten times the resistance, any small temperature variation generates a proportionally more significant change in the electrical signal. The result is an "easier" reading for simple electronics, with better resolution without the need for complex amplification. The Pt100, while less sensitive in this respect, is recognized for its stability and precision in more demanding measurements, especially when combined with appropriate instrumentation.
Pt100 is frequently used in critical applications, such as reactors and systems with strict thermal control, where long-term reliability outweighs ease of reading. In these situations, it is common for the probe to be installed externally and protected by materials such as PTFE, ensuring chemical resistance in environments with aggressive solvents.
On the other hand, the Pt1000 gains ground in more compact systems or those with simplified electronics. In these systems, the higher resistance helps reduce signal loss along the circuit, allowing for stable measurements even without advanced compensation features. Furthermore, these sensors are often integrated directly into the heating point, with stainless steel housings, or even glass when there is a risk of corrosion.
Ultimately, it's not about which is "better," but about suitability.
Where is the Pt100 most commonly used today?
The use of Pt100 extends far beyond a single sector. It appears in different contexts, whenever temperature needs to be monitored precisely. Chemical, food, pharmaceutical industries, and air conditioning systems are some of the most common examples. In all these cases, the sensor acts as a key component to ensure safety and efficiency.
Why is the Pt100 so valued in the industry? The answer lies in the set of features it delivers.
The sensor combines precision, stability, and repeatability. In industrial processes, this means less error, more control, and higher quality in the final result.
Furthermore, its near-linear response simplifies integration with automation systems, reducing project complexity.
The operating range varies depending on the sensor model and construction. In standard industrial applications, it typically operates up to approximately 420 °C. In special versions, this limit can reach 850 °C or more.
For laboratory use, there are models designed for even higher temperatures, but always within the manufacturer's specifications.
Ensuring the sensor's lifespan in harsh environments.
In many industrial applications, the Pt100 sensor cannot be installed directly in contact with the fluid, especially when dealing with high pressure, flow velocity, or chemically corrosive substances. For these cases, the use of a protective well is essential.
The well acts as a mechanical barrier that isolates the sensor rod from the harsh environment, without impeding the heat exchange necessary for reading. In addition to protecting against premature wear and oxidation, this assembly allows maintenance or replacement of the sensor to be performed without interrupting the process or emptying the pipeline.
Investing in a sensor with a suitable protective well is the final step to ensure that your plant instrumentation operates with maximum reliability and minimal unplanned downtime.
Looking for the ideal solution for your production line? A Total We offer complete sets of sensors and thermowells designed to meet the challenges of your industry.
Want to know more about the products? Contact us contact Alutal.
FAQ – PT100
The PT100, a widely used resistive temperature detector (RTD), maintains a resistance of 100 ohms at 0 °C and 138,5 ohms at 100 °C. It is a popular choice for temperature measurement in industrial processes and laboratories, valued for its stability, accuracy, and consistency.
PT100 refers to a type of temperature sensor with a platinum resistive element. "PT" stands for platinum and "100" indicates its nominal resistance at 0 degrees Celsius. PT100 sensors are widely used for precise temperature measurements in various industrial and scientific applications.
The operating principle of the PT100 is based on the variation of the electrical resistance of a platinum (Pt) wire with temperature. The sensor's resistance increases linearly with temperature, following the Callendar-Van Dusen equation. This resistance variation is used to measure temperature accurately, making PT100 sensors widely used in industrial and scientific applications.
