The features and applications of Analog environmental chambers options: choice of volume 2, the choice of the temperature range, 3 humidity range of options, 4 control mode selection, temperature rate select the [the Coors company] professional test chamber 400-6789-291
1, volume selection
Will test products (components, components, parts or whole) placed in the the climatic environmental chamber test, in order to ensure the product around the atmosphere is try to meet the environmental test conditions required by the test specification the climate chamber size of the work with products outside dimensions should follow the following rules:
a) the volume of the test product (W × D × H) shall not exceed the effective working space of the test chamber (20 to 35)% (recommend use 20%). Recommended for fever test selection is not greater than 10%.
b) is the the windward sectional area of the test product on the sectional chamber studio total area ratio of not greater than (35 ~ 50)%, (recommend use 35%).
the outline surface c) were the distance from the wall of the test chamber for at least 100 ~ 150mm, (recommended use 150mm).
These three requirements are actually interdependent and unified. 1 m3 cube boxes, for example, the area ratio of 1: (0.35 ~ 0.5) equivalent to the volume ratio of 1: (0.207 to 0.354). Away from the tank wall 100 ~ 150mm, equivalent to the volume ratio of 1: (0.343 to 0.512).
All in all these three provisions, of climate environmental chambers cavity volume should be at least 3 to 5 times the volume of the outer profile of the test product. For such a provision for the following reasons:
1] test piece placed in the box after crowding smooth channel, the channels the narrowing will lead to increase in airflow velocity. To accelerate the heat exchange between the gas stream with the test piece. This is inconsistent with the reproduction of the environmental conditions, is not realistic because the test chamber around the test piece in the standard tests are predetermined temperature environment involving air velocity should not exceed 1.7m / s, in order to prevent the test pieces and the surrounding atmosphere generator thermal conduction. The average wind speed in the no-load test chamber 0.6 ~ 0.8m / s, no more than 1 m / s, satisfy a), b) The requirement of space under area ratio, the wind speed of the flow field is likely to increase (50 ~ 100)%, with an average maximum wind speed (1 ~ 1.7) m / s. Meet the standard requirements. If the trial is not limited to increase the volume of the test piece or windward basal area, the actual test airflow wind speed will increase to beyond the highest wind speed required by the test standard, the validity of the test results will be suspect.
2] The the climate box working chamber environmental parameters [such as temperature, humidity, salt spray and sedimentation rate, etc.] the accuracy indicators are in the no-load state where the result of detection, once to be a test piece after implantation, Chambers working chamber environment uniformity of the parameter will have an impact, the greater the space occupied by the test piece, this effect is more serious. Measured test data show that the temperature difference between the flow field in the windward side and the leeward side of the 3 ~ 8 ℃, and in severe cases can be as large as 10 ℃. Therefore, it is necessary to try to meet the two requirements of a], b], and to ensure the uniformity of the environment parameter of the test products around.
3] according to the principle of heat conduction, the temperature of the airflow in the vicinity of the tank wall is usually the center of the flow field temperature difference of 2 to 3 ° C, the upper and lower limits of the high and low temperatures, but also likely to reach 5 ° C. The temperature of the walls of the box and the temperature of the flow field near the tank wall and a difference of 2 to 3 ° C (depending on the structure of the walls of the box, and the material) greater the difference between the test temperature and the external atmospheric environment, the above-mentioned temperature difference is greater, therefore, away from the tank wall (100 ~ 150mm) the space within the distance is not the use of space.
2, the temperature range of options
Currently, the range of temperature chambers abroad in general -73 ~ +177 ℃, or -70 ~ +180 ℃. The majority of domestic manufacturers typically -80 to +130 ° C, -60 to +130 ° C, -40 to +130 ° C high temperature to 150 ° C. These temperature range to meet the needs of the overwhelming majority of military, civilian products temperature test, unless there is a special need, such as the installation location near the engine and other heat source, not blindly raise the temperature limit. Because the ceiling higher the temperature, the greater the temperature difference between the inside and outside box, the worse the uniformity of the flow field inside the box. The smaller volume of available studio. On the other hand, the upper limit temperature is higher the value, the higher the heat resistance requirements on the insulation material (such as glass wool or the like) in the tank wall dissection. Case sealability requirements are also higher, so that the increase in the production costs of the case.
3, the humidity range of options
Humidity index of large domestic and foreign environmental chambers given are 20 ~ 98% RH, or from 30 to 98% RH, heat chamber dehumidification system, the humidity range of 60 to 98%, this type of test chamber can only do high wet test, but it's a much lower price. Is worth noting that in the back of the humidity indicators should indicate the corresponding temperature range, or given to the minimum dew point temperature. 1 kg of dry air containing 5 g of water vapor because the relative humidity is directly related to temperature, for the same absolute moisture content, the higher the temperature, the smaller the relative humidity, such as the absolute moisture content of 5g/kg (means ), when the temperature was 29 ° C, relative humidity of 20% RH, a temperature of 6 ℃, relative humidity of 90% RH, when the temperature was lowered to 4 ° C, relative humidity of more than 100%, to cause condensation in the housing phenomenon. Achieve high temperature, high humidity only need the water to the cabinet air steam or atomized water droplets humidification. The low temperature and humidity is relatively difficult to control, because of the absolute moisture content at this point is very low, and sometimes much lower than the absolute moisture content in the atmosphere, the need for dehumidifying the air flowing on the casing, so that the air becomes dry. Temperature and humidity of the vast majority of domestic and foreign box have adopted the principle of cooling and dehumidifying the preset indoor air in the cabinet plus a group of refrigeration fluorescent tubes. When wet air through the cooling tube, the relative humidity will reach 100% RH, condensation on the optical tube, so that the air becomes more dry air saturation. This dehumidification mode can theoretically reach the dew point temperature, but when the surface of the cold spot temperature reaches 0 ° C, the light pipe to the surface condensation of water droplets will freeze, thus affecting the heat exchange of the optical surface of the tube, so that the dehumidifying capacity decreased below zero. And sealed box not absolute, moist air in the atmosphere will seep into the housing, so that the dew point temperature rise. Other hand, the wet air flows between the light pipe only at the instant contact and the light pipe (cold spots) reaches saturation and precipitation of water vapor, this dehumidification method is difficult to make a casing dewpoint temperature to below 0 ℃. Actually achieve the minimum dew point temperature of 5 to 7 ° C. The dew point temperature of 5 ° C is equivalent to the absolute moisture content of 0.0055g/Kg temperature corresponds to a relative humidity of 20% RH for 30 ° C. If the required temperature is 20 ℃ into relative humidity of 20% RH, the dew point temperature of -3 ° C the cooling mode dehumidifying is very difficult, and must be selected air drying system can be achieved.
4, the control mode selection
Temperature and humidity test chamber constant test chamber and alternating test chamber.
Common high low temperature generally refers to a constant high and low temperature, its control method: set a target temperature, the test chamber having automatic thermostat to the capability of the point of the target temperature.High and low temperature Test chamber has a set of one or more high and low temperature changes, circulation procedures, and the ability to complete the testing process based on a preset curve, and can be in the range of maximum heating, cooling rate capability, precise control of temperature rise The cooling rate, i.e. the slope of the curve can be set to control the rate of heating and cooling. Similarly, the high and low temperature heat chamber also has a preset temperature, humidity curve, and the ability to control according to the preset. Of course, the alternating test chamber with constant test chamber, but higher manufacturing costs, because the the alternating test chamber must be configured curve automatic recording devices, process control instrument, we must solve the high temperature test chamber in the work room under the open refrigerator, etc., alternating chambers Price than constant chambers prices generally higher than 20%. Therefore, we should be realistic to the needs of the test methods as a starting point, the choice of a constant test chamber is alternating test chamber.
5, the choice of variable temperature rate
Ordinary high and low temperature cooling rate indicators, cooling from ambient temperature to the lowest temperature of the nominal time is generally 90 ~~ 120min. High and low temperature test chamber, high and low temperature heat chamber has a variable temperature and speed requirements, variable temperature 1 ° C / min rate of general requirements, speed can be adjusted in the range of this rate. Rapid change in temperature test chamber temperature rate faster heating and cooling rates up to 3 ° C / min ~~ 15 ° C / min, in certain temperature ranges are warming up, cooling rate and even up to 30 ° C / min or more. Chamber temperature range of variety, speed, rapid temperature changes are generally the same, that is -60 to +130 ° C, but the variable temperature range of the assessment of cooling rate is not the same, according to test different test requirements, rapid change in temperature test chamber range plenty of variable temperature -55 ~ +80 ℃, some -40 to +80 ° C
The rapid change in temperature test chamber temperature rate formulation, one is the whole average heating and cooling rate, a linear heating and cooling rate (in fact, every 5 min average speed). The full average speed means within the chamber of variable temperature range, the ratio of the difference between the maximum temperature and the minimum temperature and time. The foreign environmental test equipment manufacturers to provide the technical parameters of the temperature rate refers to the full average rate. Linear heating and cooling rate refers to the rate of every 5 min in an arbitrary period of time, to ensure that the temperature variations. In fact, for the rapid temperature changes Chambers, to ensure the most difficult of the linear ramp speed, the most critical period of the cooling rate in the cooling section Finally a 5 min period, the test chamber can be achieved. In some ways, linear heating and cooling rate (every 5 min average speed) is more scientific. Therefore the best test equipment has two parameters the full average heating and cooling rate and the linear heating and cooling rate (every 5 min average speed). In general, linear heating and cooling rate (every 5 min average speed throughout the average liter cooling rate of 1/2.
