The sensor Pt100 It is one of the most widely used types of resistance temperature detectors (RTDs) in industry. Known for its accuracy, stability, and reliability. But how do you ensure it continues to measure correctly over time? The answer lies in... calibration, an essential procedure for maintaining sensor performance and the quality of the processes in which it is applied.
What is a Pt100 sensor?
a sensor Pt100 It is named as such because it is made of platinum: 'Pt' is the chemical symbol for platinum. Although it is an expensive material, platinum offers greater linearity and stability than other materials. The number 100 indicates the strength of the... temperature sensor at 0 °C it is 100 Ω.
In a typical Pt100 RTD, the platinum wire is wound around a ceramic core or coil. The ceramic core contributes to stability at extreme temperatures and provides good thermal insulation against variations in ambient temperature. Additionally, the ceramic core protects the delicate platinum wire from damage.
Pt100 temperature sensors utilize the principle of electrical resistance to measure temperature. This principle states that the resistance of a metal to the passage of electric current increases with increasing temperature. This variation in resistance with temperature change is predictable, and it is this predictability that allows the temperature to be determined.
The Pt100, a platinum resistance thermometer, is one of the most accurate temperature sensors, capable of offering excellent stability and repeatability. These sensors are also relatively immune to electrical noise and therefore suitable for temperature measurement in industrial environments, especially around motors, generators, and other high-voltage equipment.
But like any high-precision measuring instrument, the PT100 sensor needs to be periodically calibrated to ensure reliable results. But what is the correct calibration method?
How is the Pt100 calibrated?
Unlike other instruments, the Pt100 sensor itself is not adjustable. That is, there is no internal correction mechanism. The process consists of comparing its readings with a high-precision reference sensor under controlled temperature and stability conditions.
Calibration is performed at specific points, for example, 0 °C, 100 °C, and 200 °C, to verify if the sensor shows deviations from the standard. The result is recorded in a calibration certificate, which indicates the error found and the test conditions.
Three methods for calibrating Pt100 sensors.
Calibration can be performed in different ways. Below, learn about the three most common methods: process calibrator, dry block, and calibration bath.
1 – Process Calibrator
The process calibrator is the most practical equipment for field checks. It simulates RTD signals and measures the system response (e.g., a 4-20 mA transmitter).
It is ideal for a quick check, ensuring that the sensor and measurement system are responding correctly. However, this method does not provide the same accuracy as a laboratory calibration.
2 – Dry block gauge
The dry block calibrator is widely used in industry. It has a metal block with holes where probes are inserted. The block is heated or cooled electrically until it reaches the desired temperature.
This method offers good stability and repeatability, making it suitable for routine calibrations of industrial sensors. However, it is important that the probe has the correct diameter for the orifice, ensuring good thermal contact.
3 – Calibration bath
The thermostatic bath is the most accurate method. In this method, the probes are immersed in a fluid under agitation, such as silicone oil, water, or ethanol, which ensures excellent thermal homogeneity.
It is the preferred method in accredited metrology laboratories because it allows calibrations with very low uncertainties, ideal for reference standards and high-accuracy sensors.
Basic calibration procedure
The process follows rigorous steps to ensure reliable results:
- Preparation: The sensor is cleaned and inspected to remove any residue or oxidation.
- Immersion: In a thermal bath, it is not mandatory that the sensor to be calibrated and the standard sensor be at the same depth, and this is not always possible. In a dry block, it is mandatory that both have their tips at the bottom of the equalization block.
- Stabilization: Wait until the temperature of the system and probes reaches stability, a step that can take 10 to 30 minutes, depending on the temperature range.
- Reading: the temperatures measured by the standard and the Pt100 are recorded at each defined point.
- Error calculation: the differences between the readings indicate the sensor's deviation from the standard.
- Issuance of the certificate: the results are documented, including test conditions, equipment used, and measurement uncertainty.
- Comply with the international standard IEC 60751, which specifies the requirements and temperature/resistance relationship for industrial platinum temperature sensors.
For a calibration to have technical validity and meet audit requirements, it needs to be traceable to national or international standards, such as Inmetro in Brazil or NIST in the United States.
Laboratories accredited according to ISO/IEC 17025 ensure that the calibration process follows rigorous criteria for control, traceability, and metrological quality.
Why calibrate the Pt100?
Even though it is a robust and reliable sensor, the Pt100 can suffer small deviations over time due to continuous use, vibration, contamination, or aging of the material. These deviations compromise the accuracy of the measurements.
Calibration is the process of comparing sensor readings to a traceable reference standard, adjusting or verifying that performance is within specified tolerances.
The main reasons for regular calibration are:
- Ensuring accuracy: incorrect readings can lead to process errors and production losses.
- Maintaining quality: incorrect temperatures directly affect the safety and performance of products.
- Meeting standards and audits: regulated sectors, such as pharmaceuticals and food, require documented periodic calibration.
- Avoid unexpected shutdowns: miscalibrated sensors can cause false alarms and control failures.
- Reduce operational costs: reliable data enables better process control and energy savings.
Where to calibrate? Alutal Calibration Laboratory
Alutal is a national leader in the manufacture of temperature sensors and also offers accredited calibration services, ensuring that each piece of equipment maintains its accuracy and compliance with market standards.
Our thermal metrology laboratory is equipped with dry block calibrators, high-stability thermostatic baths, and certified reference instruments, capable of performing calibrations across a wide range.
We have a specialized technical team, comprised of professionals trained in metrology and process control, capable of performing calibrations with traceability and issuing certificates in accordance with the standard. ISO / IEC 17025.
In addition to the calibrations in Alutal laboratoryWe also provide on-site services, reducing equipment downtime and ensuring the continuity of industrial operations.
Our technical team is ready to offer the support and precision that your process demands.
