Development of automatic verification / calibration system for temperature and humidity test equipment

Development of automatic verification / calibration system for temperature and humidity test equipment the calibration of temperature and humidity test equipment is an important measurement and calibration project which has developed rapidly in recent ten years, and it is an important source of income for many measurement institutes in thermal or physical and chemical fields Due to the heavy workload and complicated data processing, we began to develop the automatic verification / calibration system of temperature and humidity test equipment in 1997 After years of continuous upgrading of hardware and software of the automatic verification / calibration system of temperature and humidity test equipment, we have gradually accumulated some experience and experience We share with you here, hoping to be helpful for the development of similar automatic verification system 1、 The composition of the system automatic verification / calibration system is mainly composed of data collector, temperature sensor, humidity sensor, laptop (or PDA or smartphone), as shown in Figure 1 The automatic verification system can be connected with notebook computer through RS-232 or USB port, and can also be connected with smart phone (or palmtop computer) by wireless Bluetooth or other communication methods, so the system composition is convenient and flexible Especially with the popularity of smart phones, using smart phones as data display, recording and processing will become more and more convenient and popular The data collector can stack together according to the user's requirements to meet the measurement requirements of dozens of channels 2、 Problems and solutions of software and hardware system: 1) directly reflect the performance of calibrated equipment: In order to intuitively reflect the initial performance of the calibrated equipment, we use the way of real-time curve drawing, which can intuitively reflect the temperature and humidity fluctuation of the calibrated equipment According to the dispersion degree of the curve, we can intuitively reflect the uniformity of the calibrated equipment, judge whether the calibrated equipment has reached the balance through the curve intuitively, and start to record data, etc In order to distinguish the corresponding curves of each channel, we use different colors for marking, and can change the color of each channel curve at any time The system has designed up to 20 curves to meet the requirements of multi-channel temperature and humidity curve recording (as shown in Fig 2) 2) correction of sensors and data collectors: in the automatic detection system, we usually select PT100 or PT1000 platinum resistance of class A as the temperature sensing element, but even the error of platinum resistance of class A at 100 ℃ is allowed to reach ± 0.35 ℃ (Pt100 The allowable error list of platinum resistance is as follows), so it is necessary to correct the sensor and instrument in the automatic detection system The allowable temperature error of standard resistance value of industrial platinum thermal resistance level measurement range 0 ℃ (℃) class A - 200 ℃ ~ 850 ℃ 100 Ω± (0.15 + 0.002|t|) class B - 200 ℃ ~ 850 ℃ 100 Ω± (0.30 + 0.005|t|) When sending the automatic verification system for inspection, we usually use the overall calibration method of sensor and instrument for calibration In the system software, we designed the "system automatic calibration module" to calibrate the system automatically During the calibration, the sensor is placed in the water tank or oil tank After the temperature is balanced, the system automatically reads all the sensor values, inputs the actual value of the standard, and through the calibration of different temperature points, the system can automatically generate the correction values under different temperatures and save them in the database In the detection process, the automatic verification system will automatically call and calculate the correction value under the current temperature according to the sensor number, so as to ensure the accuracy and reliability of the automatic verification results 3) Problems in automatic generation of original records and certificates: The automatic verification system can automatically generate the original records and certificates that meet the requirements of laboratory accreditation However, due to the differences in the format and information content of each unit, in order to make each unit adjust the format of the original records and certificates according to their own habits, we use the database method to make the excel corresponding to the original record information The location of the table is saved in the database As long as the location of the excel table saved in the database is changed, the corresponding information can be filled in the new location, so that the user can adjust the original record and certificate format as required 4) The problem of accurate measurement of relative humidity: the temperature measurement technology is relatively mature, but there are often some problems in the field of relative humidity measurement In the early days, we used the wet and dry bulb method to measure the relative humidity, and obtained the relative humidity value by modifying the parameters such as wind speed and air pressure However, there are some limitations in the use of wet and dry ball method: ① there is no condition to ensure that the wind speed can reach 2.5m/s, so the accuracy of measurement is limited; ② the use of wet ball gauze on site, water supply and other issues need to be considered, which is cumbersome and inefficient; ③ in the environment of low relative humidity, the wet and dry ball method can not accurately measure Therefore, through many years of selection, we choose the imported temperature and humidity sensor (the relative humidity measurement accuracy is ± 1.0%), by collecting the digital signal provided by it, we can ensure the measurement accuracy of the sensor and avoid the error of a / D conversion 5) The problem of accurate measurement of thermocouple cold end temperature: in the detection of box resistance furnace, industrial annealing furnace and other high temperature furnaces, we choose K-type or S-type thermocouple as the sensor As we all know, the accuracy of cold end temperature measurement is very important for the accuracy of the whole measurement results Therefore, we use the four wire PT100 as the sensor, and the measurement accuracy is better than ± 0.05 ℃ A sealed constant temperature area is designed at the terminal of the temperature data collector to ensure that the cold end temperature is relatively stable Because it is a closed space, it is less affected by the ambient temperature The cold end temperature sensor can be easily stretched by using four wire platinum resistance measurement, which reduces the use of compensation wire, and the measurement is accurate and reliable 6) How to connect sensors conveniently and quickly: in the process of temperature field calibration, one of the more tedious work is the connection of sensors After years of choice, we have adopted two ways of connection *The standard connector of European paperless recorder is used to fix the sensor on the data collector with screws, which is suitable for units with small field detection tasks; the second method is 12 core fast connector (as shown in Figure 1), one connector can be connected to 3 A four wire platinum resistance sensor is set up, which not only improves the work efficiency of field detection, but also is easy to find and replace when there is sensor damage 7) Difficult to clean up the field sensor: in the process of temperature field calibration, another relatively cumbersome work is because the sensor leads are relatively long, sometimes like a mess in the detection process, which is difficult to clean up We have customized three kinds of two-color four core wires with manufacturers of high-temperature resistant wires, which are specially used as leads for temperature field detection, so as to prevent them from being scattered during use *The second type is round, and the fourth type is covered with a thin layer of heat-resistant material; the third type is the same as the twisted pair wire, which is twisted together by the machine Because the wires of each sensor in these three ways are not scattered, they are easier to clean up In addition, if 12 core quick connector is used, one end of the three sensors is fixed on a plug, which is easier to clean 8) Other problems solved by the software and hardware system: the software system uses the database mode to save the calibrated equipment in the database During the periodic test, it does not need to input the sample information, which reduces the workload and saves the precious time In order to improve the work efficiency of the on-site detection, the system can not only draw the curve of several calibrated equipment at the same time, but also calibrate the two equipment at the same time, without mutual interference In the process of on-site inspection, we often encounter the problem that the temperature is not balanced but we have to leave the dining room In the software system, we solve the problem by the way of delay (timing) automatic detection or cycle automatic detection, so that we only need to clean up the sensors after dinner, and improve the work efficiency In order to solve the problem that sometimes there is no power supply for on-site detection, we design a charging circuit, which is powered by a charging battery, and can work continuously for more than 24 hours without external power supply, which is convenient for on-site detection Considering that the field testing instrument needs to be portable, easy to carry, and not afraid of vibration, we specially developed a plastic mold for the data collector of this system, and carried out a reasonable structural design, which improved the reliability of the instrument while being convenient to carry 3、 Application of the system: the purpose of the automatic verification / calibration system is mainly used in constant temperature and humidity box (room), high and low temperature test box, drying box, incubator, cement curing box, water bath pot, refrigerator, cold storage, box type resistance furnace, high temperature carbon furnace Verification or calibration of temperature and relative humidity parameters of isothermal humidity test equipment As the system is actually a multi-channel high-precision temperature and humidity data acquisition and processing system, it can also be applied to the following aspects: 1) it can be used to collect, record and process temperature and humidity data in the process of research and development of products Because the system provides the function of exporting the temperature and humidity data recorded in all channels to excel, users can analyze and process the data flexibly 2) It is applied to the data recording and processing of GMP certification in pharmaceutical industry 3) it shall be used for temperature rise test of electrical equipment, circuit board, transformer, etc in electrical and electronic industry Calculate the temperature difference between the specified channels and the difference between each channel and the ambient temperature, and draw an intuitive curve to reflect the change of temperature difference 4、 Conclusion: Compared with the similar automatic detection system at home and abroad, the system has the characteristics of small size, light weight and good stability Because the software and hardware developers have many years of on-site detection experience, in the process of software and hardware development, they always consider the problems from the perspective of convenient use of the detection personnel, so the software system has the characteristics of friendly interface, in line with the on-site detection habits In the process of system development and improvement, many valuable opinions have been put forward by relevant personnel of metrology institutes such as China Academy of metrology, Shenzhen Institute of Metrology quality inspection, etc thank you