Thermal shock test chamber is a kind of test products to provide extremely high temperature and very low temperature environment and in a short period of time for cold and hot shock environmental test equipment. Mainly used in electronics, communications, materials, instrumentation, scientific research and other fields of product safety and reliability test and product screening test. In order to test the product due to thermal expansion and contraction and resulting in structural and morphological changes or physical damage, is the ideal environmental test equipment for technology development, production and quality control and other scientific research and production.
Depending on the state of the sample during the test. Thermal shock test chamber is divided into static thermal shock chamber (sample stationary) and dynamic thermal shock chamber (sample moves with the sample basket), according to the different ways of moving the sample basket, dynamic thermal shock chamber can be divided into vertical lifting and horizontal translation two types, dynamic vertical lifting thermal shock chamber is mainly used for small load (such as IC module) test, horizontal translation thermal shock chamber is mainly used for temperature shock test of large load samples.
The two-zone thermal shock chamber discussed in this article is as follows:
1) Volume in sample basket: 300 L
2) Limit temperature range: -75 ~ +220 ℃
3) Temperature impact range: -65 ~ +150 ℃
4) Temperature conversion time: < 10 s
5) Temperature recovery time: ≤ 5 min
6) Temperature deviation: ≤ ± 2.0 ℃
7) Temperature fluctuation: ≤ 0.5 ℃
1. Equipment Introduction
The thermal shock test chamber is mainly composed of a high temperature zone, a low temperature zone, a heating system, a cascading refrigeration system, a water circulation cooling system, a sample basket transmission system and a control system. Thermal shock chamber two zone are high temperature zone and low temperature zone, in the high temperature to low temperature shock test, the sample basket is first in the high temperature zone according to the set temperature for high temperature test, at this time the low temperature zone is in a pre-cooling working state. When running to the set thermal shock time, the transmission mechanism will move the sample basket from the high temperature zone to the low temperature zone. After moving to the low temperature chamber, the sample in the low temperature chamber according to the set temperature for low temperature test. At this time the high temperature zone is in the preheating working state, in the process from low temperature to high temperature shock test, the process is the opposite of the above.
The main control requirements of this test chamber are:
1) In order to meet the working requirements of the test chamber pre-cooling temperature of -75℃ and temperature recovery time of <5 min. The refrigeration system adopts the refrigeration method of binary cascading refrigeration cycle, which puts forward certain requirements in the starting sequence of the two compressors and the control of many refrigeration valves and bypass valves, especially in the process of temperature shock, the regulation and control of the cooling amount will directly affect the accuracy of temperature control.
2) The high temperature zone and the low temperature zone are equipped with high-power heaters, in the process of temperature shock, it is necessary to solve the contradiction of rapid heating and precise temperature control, which puts forward higher requirements for the control of the heater, in addition, the low temperature zone heater also needs to have a defrost function.
3) The sample basket transmission system adopts a chain transmission mode with high transmission efficiency, and when the temperature is impacted, strict requirements are put forward for the control of the transmission motor and the accurate positioning of the sample basket movement, and the accuracy of the sample basket positioning will directly affect the sealing of the low temperature chamber and the high temperature chamber, which in turn will affect the temperature reduction speed and temperature control accuracy.
4) In order to ensure the operation safety of the thermal shock test chamber, the control system sets up a large number of alarm protection information, such as chamber door switch, water pressure alarm, overheating protection, compressor overload protection, etc., which puts forward reliability requirements for the alarm signal processing of the control system.
2. Realization of hot and cold temperature shock
The cyclic temperature shock of 85 °C high temperature and -55 °C low temperature is introduced as an example. Before start, the editing test process is first set up through the touch screen interface of the thermostat. When starting, the sample basket containing the sample will automatically determine the direction of movement according to the position. After moving to the high temperature zone, the two side walls of the sample basket will divide the inside of the thermal chamber into two independent closed spaces, and the high temperature zone where the sample basket is located will start the heater for 85 ° C high temperature control test, and at this time the low temperature zone will start the refrigeration unit for -70 °C pre-cooling temperature control test. When the high temperature zone running time reaches the set 60 min, the PLC will receive the end signal of the high temperature test issued by the thermostat, the system will control the mobile motor to drive the sample basket from the high temperature zone to the low temperature zone to move rapidly. In the process of moving, the low temperature zone and the high temperature zone will carry out a short period of cold and hot air convection. While the sample load in the sample basket will also bring the heat in the high temperature zone into the low temperature zone, the temperature in the low temperature zone will rise rapidly in a short period of time. And within the 10 s temperature conversion time, the sample basket will quickly move into place.
When the low temperature test running time reaches 45 min, PLC will receive the end signal of the low temperature test, the system will control the sample basket from the low temperature zone to the high temperature zone to move rapidly. Similarly, during the movement, the high temperature zone temperature will increase due to a large amount of cold into the air. When the sample basket is quickly moved to the position, the system will start the high temperature zone heater at full power to heat up rapidly. And the temperature will return to 85 ℃ within five minutes, at which time the low temperature chamber will carry out -70℃ pre-cooling temperature control test. When the number of cycles is complete, the entire temperature shock cycle experiment ends.
The low temperature zone also has an automatic defrosting function. After the end of the thermal shock test, the defrosting temperature and running time can be set through the touch screen. So the low temperature zone for defrosting work, reduce the occurrence of frost in the low temperature zone. It is conducive to protecting the refrigeration unit.
3. Conclusion
The two-zone thermal shock test chamber control system realizes the working requirements of high and low temperature shock of the test chamber, solves the contradiction between rapid temperature rise and fall and temperature control during temperature shock, and the sample basket transmission is stable and the seal is reliable. At present, the test chamber is running well in the user manufacturer.