The calibration method of platinum resistance ultra-high precision thermometer is mainly used to ensure the accuracy and reliability of the thermometer. Due to its high accuracy and stability, platinum resistance thermometers are widely used in scientific research, industry, and laboratory environments. The following are common calibration methods for platinum resistance ultra-high precision thermometers:
1、 Calibration preparation work
Prepare standard thermometer
Choosing a high-precision standard thermometer usually uses internationally recognized standard thermometers (such as the International Temperature Scale ITS-90) for comparison.
Ensure that the accuracy and stability of the standard thermometer meet the requirements and have been pre calibrated.
environmental conditions
Calibration should be carried out under constant environmental conditions, with stable temperature and humidity to reduce the influence of external factors on the calibration results.
Usually, temperature fluctuations are required to be within ± 0.1 ° C, and humidity should be controlled between 40% -60%.
Calibration equipment
Use temperature control devices (such as constant temperature bath, dry heater, freezing point bath, etc.) to maintain the test medium (such as water, oil, ice, liquid nitrogen, etc.) within the desired temperature range.
Ensure that the interface of the temperature sensor is clean and undamaged to avoid errors caused by poor contact.
2、 Calibration steps
Zero point calibration (freezing point calibration)
Prepare a freezing point tank: Prepare a mixture of ice and water, ensuring a 1:1 ratio and a stable temperature of 0 ° C (or ± 0.1 ° C). The freezing point trough provides a known and stable temperature reference.
Temperature measurement: Place the platinum resistance thermometer and standard thermometer separately in an ice water mixture, ensuring that the probe is fully immersed and maintaining it for sufficient time until the temperature stabilizes.
Record temperature readings: Compare the readings of the platinum resistance thermometer with the standard thermometer, adjust the zero point of the platinum resistance thermometer (i.e. the deviation at 0 ° C) until the two readings are consistent or close.
Mid point calibration (vapor saturation point calibration)
Prepare steam saturation point: Prepare a boiling water tank to ensure stable boiling point of water. Normally at atmospheric pressure, the boiling point of water is 100 ° C. Its accuracy can be improved by precisely controlling the water temperature and adding sufficient pressure.
Temperature measurement: Place both the platinum resistance thermometer and the standard thermometer into boiling water at the same time, ensuring that both probes are fully immersed and the water surface is stable. Maintain a certain amount of time until the temperature stabilizes.
Record temperature readings: Compare the readings of platinum resistance thermometers with standard thermometers and make necessary adjustments.
High temperature calibration (using a temperature controlled furnace)
Using a temperature controlled furnace: For high temperature ranges exceeding 100 ° C, a high-temperature furnace (such as a metal furnace) can be used for calibration. Ensure that the temperature of the temperature controlled furnace is stable and can be accurately controlled to the desired temperature point.
Calibration point selection: Select multiple temperature points for calibration, commonly used high temperature calibration points include 200 ° C, 500 ° C, 1000 ° C, etc.
Measurement and adjustment: Place the platinum resistance thermometer and standard thermometer together in the furnace, ensuring the stable position of the probe and reaching the set temperature. Record and compare the readings of both, adjust the reading of the platinum resistance thermometer to ensure consistency with the standard thermometer.
Multi point calibration
To ensure the accuracy of high-precision thermometers throughout the entire temperature range, calibration needs to be performed at multiple different temperature points in addition to zero and vapor saturation points. It is usually recommended to choose 5-10 different temperature points (such as -40 ° C, 0 ° C, 50 ° C, 100 ° C, 200 ° C, etc.).
Measure the temperature at each point and adjust the reading of the platinum resistance thermometer to ensure it matches the standard thermometer.
Inspection after calibration is completed
Record the results: Record the temperature readings of each calibration point and calculate their error. If the calibration results meet the requirements, the final calibration can be carried out.
Adjust the instrument: Adjust the platinum resistance thermometer based on the calibration results to ensure accurate readings. For most high-precision thermometers, calibration or adjustment can be done through software.
3、 Verification after calibration
Reverse verification
After completing the initial calibration, the thermometer can be moved to another identical standard environment (such as different temperature control tanks or calibration equipment) to verify whether the previous calibration results are still valid.
If there is a significant deviation in the calibration data, recalibration should be performed.
Periodic calibration
Regularly calibrate and check the thermometer according to its usage and accuracy requirements. Generally speaking, ultra-high precision thermometers are calibrated comprehensively once a year or more frequently according to actual needs.
4、 Common calibration problems and solutions
The reading is unstable
Check if the probe is in sufficient contact with the test medium. Ensure a stable testing environment and eliminate interference from surrounding air flow.
Ensure that all cables are well connected to avoid unstable readings caused by poor contact or interference.
The thermometer deviation is too large
If the deviation of the thermometer exceeds the standard requirements, it may be necessary to adjust the hardware of the thermometer or use a more accurate standard thermometer for recalibration.
Instrument aging
Long term use of platinum resistance thermometers may result in performance degradation. Regularly check its resistance value and update the equipment or perform stricter calibration in a timely manner.
Through these precise calibration steps, it can be ensured that the platinum resistance ultra-high precision thermometer maintains high accuracy during the measurement process, meeting various high demand applications.