Standard for measuring humidity in environmental test chamber

Humidity measurement standard in environmental test chamber most of the humidity measurement in environmental test chamber adopts the low-cost wet and dry bulb method In the case of high humidity (80-100% RH), the temperature difference between wet and dry bulb is 1 ℃, corresponding to the relative humidity difference of about 5% According to the principle that the accuracy of the test device should not be less than one third of the tolerance of the test conditions (see the national military standard gjb150.1-86), the temperature difference of 1 ℃ requires that the tolerance of the temperature measurement of the dry ball and the wet ball itself is ± 0.7 ℃, and then the hydraulic pressure of the temperature measurement accuracy reaches 0.2 ℃ By analogy, the relative humidity error of constant damp heat test chamber is ± 3% RH The temperature measurement accuracy shall be ± 0.1 ℃ Therefore, the error of measuring relative humidity by using the wet and dry bulb method is usually ± (3 ~ 5)% RH The temperature measurement accuracy is such that the humidity control accuracy can be imagined In order to overcome the shortcomings of low measurement accuracy of wet and dry bulb method, which is greatly influenced by human operation, solid humidity sensor (such as capacitive humidity sensor) has been applied to environmental test equipment after solving the problem of low temperature (- 55 ~ 70 ℃), and its measurement accuracy can reach ± 1 ~ 3% RH The accuracy of humidity control is not only restricted by the means of humidity measurement, but also related to the way of humidification There are many ways of humidification in the environmental test chamber There are three general ways: 1) water disk humidification It can be divided into natural evaporation and electric heating evaporation, the rate of which is slow The control accuracy is low, and it is mostly suitable for constant temperature and humidity box 2) spray steam for humidification The humidification speed is fast, but the humidification fluctuation is large, it is easy to achieve rapid control, and the control accuracy is good However, due to the injection of 100 ℃ steam, there will be a small amount of interference to the temperature state in the tank 3) atomized water The particle diameter of atomized water is about 10 ~ 50 μ This method has the advantages of steam spraying and humidification, and it does not need external steam boiler, and it can adjust the temperature of spray particles to be the same as the test temperature in the tank, so it is a better humidification method Analysis of the condition of temperature and humidity test equipment 1) the production of temperature and humidity environment test equipment is a mechanical manufacturing industry that has lasted for decades, and its basic technology (such as refrigeration, heating) has been mature However, with the progress and development of industrial technology, many new application technologies are constantly introduced into environmental test equipment, such as computer technology, fuzzy control theory, multi box synchronous operation, etc., so it is difficult to give manufacturers the next arbitrary conclusion which is better or worse The scale equipment produced by each manufacturer with decades of manufacturing experience can be used, and its working principle, applied technology, even structure and material have many similarities As long as the manufacturer is careful in management and responsible for quality (such as through ISO9000 demonstration), its products have existing conditions and use value 2) although the working principle and application technology of environmental test equipment at home and abroad are basically the same, there is still a gap in the following three aspects of drug stability test box, resulting in high failure rate in the use of environmental test equipment produced at home and abroad, and the continuous guarantee period of performance index is shorter than that at home and abroad A) the quality of components and parts is relatively poor, especially the electronic components of refrigeration compressor unit, expansion valve, main channel solenoid valve and control system Most of the failures of domestic environmental test equipment are caused by the quality and service life of components and parts B) the production process is relatively backward Production process and equipment, including the technical level of construction personnel, have a great impact on the service life of products For example, the pipeline layout in the refrigeration system involves the resonance of the pipeline in operation, the loss along the refrigerant process, the convenience of maintenance, and the smooth recovery of compressor oil Such as welding process and quality of pipeline, pipeline cleaning and leak detection technology The production equipment (such as numerical control variable plate, numerical control elbow, nitrogen filled protective welding machine, etc.) can be purchased quickly with money, but the production process is a long-term experience accumulation process, which can not be achieved overnight c) Quality control of production process The quality control of domestic production process is far less strict than that of foreign companies, so there are many hidden dangers of equipment These hidden dangers will be gradually exposed in use and form faults The quality control of the production process is related to the management level and production habits of the manufacturers The demonstration of ISO9000 is a sign that the quality control of the production process is standardized.