Calibration and maintenance of environmental testing equipment

Calibration

Environmental test equipment is calibrated according to JJF1101-2003, “Specifications for Temperature and Humidity Calibration of Environmental Test Equipment.” This specification applies to the calibration of the temperature and humidity measurement performance of environmental test equipment, and other similar equipment can also be calibrated according to this specification. Therefore, for environmental test equipment using liquids (such as water or oil) as heat transfer media, for which relevant national calibration specifications have not yet been issued, JJF1101-2003 can also be used for calibration. Calibration of parameters other than temperature and humidity in environmental test equipment (such as gas concentration and light intensity) can be performed using a gas concentration detector and an illuminometer.

Before calibration, the equipment being calibrated should be powered on to ensure that it has reached a constant temperature and humidity state. Only then should standard temperature and humidity sensor probes be deployed for calibration. When calibrating conventional air-based environmental test equipment, sensor probes should be deployed according to the calibration specifications, ensuring rapid, accurate, and even placement. The spacing between probes and between probes and the inner wall should be carefully controlled (generally no less than 1/10 of the length of each side). Try to avoid opening the door of the equipment for a long time, which will cause the temperature and humidity inside and outside to exchange too long and too frequently, thus affecting the storage and cultivation of the specimens inside, or causing the re-regulation of constant temperature and humidity to take too long, affecting the calibration efficiency. During calibration, environmental test equipment with controllers that have parameter settings and displays, such as electric constant temperature incubators (drying) boxes, biochemical incubators, and cement concrete constant temperature and humidity curing boxes, are usually calibrated for their set points or set ranges; environmental test equipment that has no temperature controller setting and temperature display functions and only mechanical or analog temperature adjustment devices, such as drug refrigerators and freezers used in medical institutions, should be calibrated according to their actual use and customer needs. For example, refrigerators used for cold chain storage of drugs, reagents, and vaccines are calibrated at 2°C to 8°C, blood refrigeration is 3°C to 5°C, and plasma is frozen and stored at less than -18°C. For the two types of environmental testing equipment mentioned above, if the measured temperature exceeds the set or required error range during calibration, the customer should be notified promptly and, if necessary, commissioned. For controllers equipped with a calibration function, error correction can be performed within the controller. For those without a calibration function and only with an adjustment device, gradual adjustments and measurements should be made until the temperature reaches the specified requirements and error range.

Due to the high thermal conductivity and high fluctuations of liquid media, many medical, pharmaceutical, and food laboratories utilize temperature measurement equipment (such as constant temperature water baths, blood circulation thawing chambers, and disintegration apparatus) that uses water or oil as a heat transfer medium. These devices are typically set to operate at temperatures between 36°C and 37°C, simulating human body temperature. This allows specimens (such as body fluids and biopsy specimens) to be stored in test tubes or other containers for temporary preservation, or for thawing and reconstitution of frozen blood. If the required operating temperature exceeds 100°C, oil is used as the heat transfer medium. During calibration, due to the excellent temperature uniformity and fluctuations after constant temperature operation and its relatively small size, the measurement points can be arranged based on JJF1101-2003. Depending on the actual situation, the number of measurement points can be reduced to one central point plus two or four peripheral points.

II. Operation and Maintenance

For equipment that uses electric heating coils to control temperature, such as desiccators and incubators, the heating coils are typically installed at the bottom of the equipment. During operation, sample containers should be placed in the middle layer, and items should not be overcrowded. The fan function should be enabled as much as possible to circulate air within the equipment to ensure good temperature uniformity. For equipment that uses a refrigeration compressor to control temperature, such as refrigerators and mold incubators, the equipment should not be placed too close to the wall during operation, with a distance of at least 10 cm. Avoid excessive items stacked around the equipment to prevent heat dissipation. Especially in environments with high operating temperatures, proper ventilation is essential to ensure proper cooling performance. Household items, food, and water should not be placed inside the device. First, they can contaminate the internal environment. Second, excessive moisture can cause severe ice formation in the refrigerator and freezer compartments, affecting normal operation. If significant deviations or refrigeration failure occur, check the gear adjustment for proper adjustment and the refrigerant in the compressor for leaks. Therefore, regularly check the water level in the small water bottle and humidifier during use and refill water regularly. If the actual humidity inside the device is significantly lower than the displayed value, first check for condensation on the exposed air sensor or a lack of water in the small water bottle. If so, wipe the exposed air sensor dry or refill the small water bottle. If the humidity consistently fails to reach the preset value, open the device and check the humidifier for damage or a lack of water. Regularly clean the interior and exterior of the device and the surrounding environment, especially the drying (incubation) chamber. Keep the surrounding environment clean to prevent mice from entering the device and chewing through internal wiring, potentially damaging the device.

For liquid-based environmental testing equipment, due to its operating principle, the internal liquid level should be constantly monitored during use. At a minimum, the liquid level should submerge both the sensor and the heating element to prevent burnout. For example, in a water bath, when the sensor loses contact with the water, the object being monitored becomes air. The temperature controller will not receive the correct temperature signal feedback from the water, causing it to continuously control the heating element, ultimately causing it to burn out or even cause a fire. Repairs to the above equipment, including replacements of temperature controllers, sensors, and other components, require re-commissioning and recalibration.