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 that has developed rapidly in the past decade. It is an important source of income for many thermal or physical and chemical professions. Due to the heavy workload and complicated data processing, we started to develop the automatic verification / calibration system for temperature and humidity test equipment in 1997. After years of continuous upgrading of hardware and software for automatic verification / calibration of temperature and humidity test equipment , we gradually accumulated some experience and Experience, share with everyone here, I hope to be able to help the development of similar automatic verification system.
First, the composition of the system
Automatic verification / calibration data acquisition system consists of a temperature sensor, a humidity sensor, a laptop (PDA or PDA or smart phone), as shown in Fig.
Automatic verification system can be connected via RS-232 or USB port of a laptop computer, you can also use the wireless Bluetooth (Bluetooth) or other means of communication and smart phone (or PDA) is connected, convenient and flexible system. Especially with the popularization of smart phones, it will become more and more convenient and popular to use smart phones as data display, recording and processing. Data collectors can be stacked together according to user requirements to meet the measurement requirements of dozens of channels.
Second, the problems and solutions solved by the software and hardware systems:
1) Visually reflect the performance of the calibrated device:
In order to visually reflect the initial performance of the calibrated equipment, we use the real-time curve drawing method, which can intuitively reflect the temperature and humidity fluctuations of the calibrated equipment. According to the degree of dispersion of the curve, the uniformity of the calibrated equipment can be visually reflected. You can use the curve to visually determine whether the school equipment is in balance, whether you can start recording data, and so on. To distinguish the curves for each channel, we mark them in different colors and change the color of each channel curve at any time. The system has designed up to 20 curves to meet the recording requirements of multi-channel temperature and humidity curves. (Figure 2 )
2) Correction of sensors and data collectors:
In the automatic detection system, we usually use a Class A Pt100 or Pt1000 platinum resistance temperature sensing element, but even in class A platinum resistance
Industrial Platinum Thermal Resistance Level | Measuring range | Temperature tolerance ( °C ) | |
Class A | 100Ω | ± ( 0.15+0.002|t| ) | |
Class B | 100Ω | ± ( 0.30+0.005|t| ) |
 When sending the automatic verification system, we usually use the sensor and the overall calibration of the instrument to calibrate. In the system software, we designed the “ system automatic calibration module †to automatically calibrate the system. When calibrating, the sensor is placed in the water tank or oil tank. After the temperature is balanced, the system automatically reads all the sensor values ​​and inputs the actual value of the standard. The temperature point is calibrated and the system automatically generates correction values ​​at different temperatures and stores them in the database. During the detection process, the automatic verification system will automatically call and calculate the correction value at the current temperature according to the sensor number, thus ensuring the accuracy and reliability of the automatic verification result.
3) The original record and the certificate automatically generated:
The automatic verification system can automatically generate the original records and certificates that meet the laboratory's approval requirements. However, because each unit's certificate format and information content are different, in order to enable each unit to carry out the original records and certificate formats according to their own habits. adjust the way we use the database, the database will be stored in the original record information corresponding to the position of the excel table, as long as the change in location database stored excel table, you can fill in the corresponding information to a new location, the realization Users can adjust the original record and certificate format as needed.
4) Problems with accurate measurement of relative humidity:
Temperature measurement techniques are relatively mature, but there are often problems with this or that in the field of relative humidity measurement. In the early days, we used the dry and wet bulb method to measure the relative humidity, and obtained the relative humidity value by correcting the parameters such as wind speed and air pressure. However, the use of dry and wet ball method has certain limitations , 1 because there is no condition to ensure that the wind speed can be achieved.
5) The problem of accurate measurement of the temperature of the cold junction of the thermocouple:
In the detection of high-temperature furnaces such as box-type resistance furnaces and industrial annealing furnaces, we choose K -type or S -type thermocouples as sensors. It is well known that the accuracy of the cold junction temperature measurement when using a thermocouple for detection is critical to the accuracy of the overall measurement. Therefore, we use the four-wire Pt100 as the sensor, and the measurement accuracy is better than ±
6) How to connect the sensor conveniently and quickly:
In the temperature field calibration process, a more tedious task is the connection of the sensor. After years of choice, we have used two connections. * A standard connector using European paperless recorder, screwed to the data collector with screws, this method is suitable for on-site inspection of small units; the second method uses 12- core quick connector (Figure 1 ), one connector can be connected to three four-wire platinum resistance sensors, which not only improves the efficiency of on-site inspection, but also makes it easy to find and replace when there is damage to the sensor.
7) The problem of the on-site sensor is difficult to clean up:
In the temperature field calibration process, another cumbersome work is that the sensor leads are relatively long, and the detection process sometimes resembles a mess and is difficult to clean up. We have custom-made three-color four-core wire for the manufacturer of high-temperature wire, which is used for temperature field detection to prevent it from being scattered during use. *The type is four-wire side-by-side flat type, which is covered with a thin layer of high temperature resistant material; the second type is round, and the four lines are covered with a thin layer of high temperature resistant material; the third type is the same as the twisted pair wire by the machine. The four wires are twisted together. The lines of these three methods are easier to clean because the lines of each sensor are not scattered. In addition, if a 12- pin quick connector is used, it is easier to pack one end of the three sensors on one plug.
8) Other problems solved by the software and hardware system:
The software system uses the database method to store the calibrated equipment in the database in the past year. It does not need to input sample information during the period detection, which reduces the workload and saves valuable time.
In order to improve the efficiency of on-site inspection, the system can simultaneously depict the curves of multiple schools, and can also calibrate two devices at the same time without interfering with each other.
In the process of on-site inspection, it is often encountered that the temperature is not balanced yet to leave the meal. In the software system, we solve it by delay (timed) automatic detection or automatic loop detection, so that we only need to pack the sensor after the meal, which improves the work efficiency.
In order to solve the problem that sometimes there is no power supply in the field detection, we design the charging circuit, which is powered by the rechargeable battery. It can work continuously for more than 24 hours without external power supply, which is convenient for on-site inspection.
Considering that the on-site inspection instrument needs to be light, easy to carry, and not afraid of vibration, we have specially developed a plastic mold for the data acquisition device of this system, and carried out reasonable structural design, which also improves the reliability of the instrument while being convenient to carry. .
Third, the application of the system:
The purpose of the automatic verification / calibration system is mainly for constant temperature and humidity chamber ( room ) , high and low temperature test chamber, drying oven, incubator, cement curing box, water bath, refrigerator, cold storage, box resistance furnace, high temperature carbon Furnace ... Verification or calibration of temperature and relative humidity parameters of isothermal and humidity test equipment. Since 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) The collection, recording and processing of temperature and humidity data used in research and development of products. Since the system provides the function of exporting temperature and humidity data recorded by all channels to the excel table, the user can flexibly analyze and process the data.
2) Applied to the GMP certification of the pharmaceutical industry for data recording and processing of the test process.
 3) Temperature rise experiments for electrical equipment, circuit boards, transformers, etc. used in the electrical and electronic industry. Calculate the temperature difference between the specified channels, the difference between each channel and the ambient temperature, and draw an intuitive curve to visually reflect the change in temperature difference.
Fourth, the conclusion:
Compared with similar automatic detection systems at home and abroad, the system has the characteristics of small size, light weight and good stability. Because software and hardware developers have many years of on-site inspection experience, in the process of software and hardware development, it is always convenient to detect. The perspective of personnel use is considered. Therefore, the software system has a friendly interface and meets the characteristics of on-site testing. In the process of system development and improvement, the relevant personnel of the Institute of Metrology, China Institute of Metrology and Quality Measurement, etc., have put forward many valuable opinions. Thank you.
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