High and low temperature cold and hot cycle integrated machineAs a core equipment for environmental testing, it is widely used in high and low temperature cycle reliability testing in fields such as electronics, materials, and automobiles. The core calibration objective is to correct key parameter deviations such as temperature control accuracy, temperature uniformity, heating and cooling rate, and cycle timing, ensuring the authenticity and reliability of experimental data. This guide is based on JJF 1101-2019 "Calibration Specification for Temperature and Humidity of Environmental Testing Equipment" and provides a standardized calibration plan for the entire process, taking into account the operating characteristics of the equipment.

1、 Core preparation before calibration

Before calibration, equipment status checks, selection of standard instruments, and environmental control must be completed to avoid calibration errors caused by early factors.

1. Preparation of standard instruments and tools

Core standard instruments: high-precision temperature inspection instrument (accuracy ≥ ± 0.05 ℃, resolution 0.01 ℃), standard platinum resistance thermometer (Pt100, Class A, tolerance ± (0.15 ℃+0.002 | t |)), stopwatch (accuracy 0.01s), temperature and humidity meter (accuracy ± 1 ℃, ± 5% RH); If the device has a humidity function, an additional high-precision humidity generator (accuracy ± 2% RH) needs to be prepared.

Auxiliary tools: calibration bracket (used to fix temperature sensors and ensure accurate measurement point positions), insulated gloves, screwdriver (used to open equipment testing holes), data recording form (including temperature, time, deviation and other fields), equipment operation manual.

Instrument verification: All standard instruments must be CNAS certified and within the calibration validity period. Before calibration, they need to be preheated for 30 minutes to ensure stable performance.

2. Equipment and environmental preparation

Equipment status check: Confirm that the appearance of the all-in-one machine is not damaged, the door seal is well sealed without deformation, and the heat dissipation port is not blocked; After connecting the power, start the machine for trial operation and check that the refrigeration system, heating system, and circulating fan are running normally without any abnormal noise or leakage; Clear the debris inside the test chamber, clean the oil stains and dust on the walls of the chamber.

Environmental control requirements: Calibrate the environmental temperature to 15 ℃~35 ℃, relative humidity to 30%~75%, and no strong airflow direct blowing equipment; The ambient voltage should be stable at 220V ± 10% (380V ± 10% for three-phase equipment), avoiding co line power supply with high-power equipment; Reserve at least 0.5m of operating space around the equipment to ensure heat dissipation and safe operation.

Standard layout of measuring points: The number of measuring points is determined based on the equipment volume (9 measuring points are set for volume ≤ 1m ³, and 15 measuring points are set for volume 1-10m ³), and the "five point method" is used for point layout - the front, middle, and back of the box are distributed in three dimensions, with a distance of ≥ 100mm from the box wall, door, and bottom. Standard sensors are fixed by brackets to avoid direct contact with the box wall.

2、 Key parameter calibration practical process

Calibrate in the order of "temperature accuracy → temperature uniformity → heating and cooling rate → cycle timing", and record the deviation of each parameter after calibration and correct it in a timely manner.

1. Temperature control accuracy calibration

The deviation between the actual temperature and the set value of the calibration equipment at the set temperature covers key nodes throughout the entire temperature range of the equipment.

Step 1: Set the calibration temperature point

Select at least 5 calibration points based on the rated temperature range of the equipment (such as -70 ℃~150 ℃), including lower limit value, upper limit value, intermediate value, and two commonly used test temperatures (such as -60 ℃, 0 ℃, 50 ℃, 100 ℃, 140 ℃).

Step 2: Constant temperature and data acquisition

Set the device to the first calibration point and start running; After the temperature stabilizes (with a fluctuation amplitude of ≤± 0.5 ℃ for 30 minutes), start collecting data, record the temperature values of the standard thermometer and equipment display screen every 10 minutes, and continuously collect 3 sets of data.

Step 3: Deviation Calculation and Correction

Calculate the average temperature value of each measuring point, and the difference between it and the set value of the equipment is the temperature deviation; If the deviation exceeds the equipment tolerance (usually ± 1 ℃), adjust it through the "temperature correction" function of the equipment control system - for example, if the actual average temperature is set to 51.2 ℃ at 50 ℃, set the correction value to -1.2 ℃, and repeat the test after correction until the deviation is qualified.

2. Temperature uniformity calibration

The temperature consistency of different measuring points in the calibration test chamber is a key indicator for evaluating the effectiveness of equipment testing.

Step 1: Constant temperature stability

Select commonly used temperature points for the equipment (such as 25 ℃, 85 ℃, -40 ℃), set the equipment and run it. After the temperature stabilizes, maintain it for 60 minutes to ensure a uniform temperature field inside the box.

Step 2: Multi point synchronous acquisition

Synchronize the collection of temperature data from all measuring points using a temperature inspection instrument, collecting data every 5 minutes for 6 consecutive times, and record the temperature values of each measuring point.

Step 3: Uniformity Calculation and Adjustment

Calculate the difference between the maximum and minimum temperatures of all measurement points collected each time, and take the average of the 6 differences as the temperature uniformity; If the uniformity exceeds the tolerance (usually ≤ 2 ℃), check whether the speed of the circulating fan is normal. If the speed is insufficient, adjust the fan parameters; If the local temperature deviation is too large, the position of the guide plate inside the box can be adjusted, corrected, and recalibrated.

3. Calibration of heating and cooling rate

The rate deviation of the calibration equipment from one temperature point to another directly affects the test cycle and effectiveness.

Step 1: Set the speed test interval

Select typical temperature ranges, such as low temperature range (-60 ℃ → 25 ℃) and high temperature range (25 ℃ → 100 ℃), and record the temperature values of the two endpoints (T1, T2).

Step 2: Speed testing and timing

Start the temperature rise and fall program of the device, press the stopwatch to count when the temperature reaches T1, stop timing when the temperature reaches T2 and stabilizes (fluctuation ≤± 1 ℃), and record the time consumption t (minutes); At the same time, the temperature monitoring instrument is used to record the temperature change curve throughout the entire process and verify that there are no abnormal fluctuations.

Step 3: Rate Calculation and Correction

Calculate the actual temperature rise and fall rate: rate v=| T2-T1 |/t; If the deviation from the nominal speed of the equipment (such as 5 ℃/min) exceeds ± 10%, it is necessary to check whether the refrigerant in the refrigeration system is sufficient and whether the power of the heating tube is normal. If the refrigerant is insufficient, it needs to be supplemented. If the heating tube is aging, it needs to be replaced and adjusted before retesting.

4. Cycle timing calibration

Calibrate the accuracy of temperature holding time and transition time for each stage of the high and low temperature cycle mode of the equipment.

Step 1: Set the loop program

Write a typical loop program, such as "-40 ℃ hold for 30 minutes → heat up to 85 ℃ (rate 5 ℃/min) → 85 ℃ hold for 30 minutes → cool down to -40 ℃ (rate 5 ℃/min)", save the program and start it.

Step 2: Time series data collection

Record the key time points of each stage with a stopwatch: the time when the temperature drops to -40 ℃, the time when the temperature starts to rise, the time when the temperature rises to 85 ℃, and the time when the temperature starts to drop. Calculate the actual holding time and transition time of each stage.

Step 3: Timing correction

If the actual time deviates from the set time by more than ± 5% (if the set time is kept for 30 minutes, it is actually 32 minutes), adjust the timing parameters through the device program editing function, and focus on checking whether the rate settings of the heating and cooling stages match the actual situation. After correction, repeat the cycle test until the timing is accurate.

3、 Verification and recording after calibration

1. Comprehensive verification testing

Select three typical calibration points (one low, one medium, and one high) and perform a complete "temperature accuracy+uniformity" joint test to ensure the stability and reliability of the corrected parameters; For devices with loop function, run a complete loop program once to verify the accuracy of temperature and timing coordination.

2. Establishment of calibration files

Establish a "one machine, one file" calibration file to record the following core information:

Equipment information: model, serial number, date of manufacture, user, installation location;

Calibration information: calibration date, calibration personnel, calibration environment temperature and humidity, standard instrument model and calibration certificate number;

Calibration data: deviation values, uniformity data, temperature rise and fall rate test records, and timing test data for each temperature point;

Correction record: Correction parameters, adjustment parts, comparison data before and after;

Verification results: comprehensive verification conclusion, whether it is qualified, and the next calibration date.

4、 Key precautions

Safety protection: When calibrating high and low temperature extreme values, it is necessary to wear insulated gloves and goggles to avoid direct contact with the box door or internal components, which may cause frostbite/burns; It is forbidden to open the box door during equipment operation. If operation is necessary, pause the operation first and wait for the temperature to return to near room temperature.

Calibration cycle: Under normal usage scenarios, it is calibrated once a year; Calibrate every 6 months under high-frequency use (running for ≥ 8 hours per day) or harsh environments (such as high dust and high corrosion); Equipment maintenance (refrigeration system, heating system) requires immediate recalibration.

Exception handling: If there is a sudden rise or drop in temperature, or a shutdown of the refrigeration system during calibration, the calibration should be stopped immediately, the equipment power should be turned off, and faults should be investigated (such as checking overload protection switches and refrigerant leaks). After troubleshooting, recalibration should be performed.

Software calibration taboos: It is prohibited to arbitrarily modify the core parameters of the equipment control system (such as PID adjustment coefficient and fan speed upper limit). If adjustments are needed, contact the technical personnel of the equipment manufacturer for guidance to avoid equipment damage caused by parameter confusion.

This guide is applicable to mainstreamHigh and low temperature cold and hot cycle integrated machineThe model and specific calibration steps need to be refined in conjunction with the equipment operation manual. If third-party authoritative calibration is required, a CNAS qualified metrology institution must be commissioned to ensure that the calibration results can be traced back to the national temperature measurement standards.