Technical Scheme of Vacuum Precision Control in Lunar Soil Environment Ground Simulation Test Device
Abstract: In the lunar exploration project, it is necessary to collect lunar soil samples in the vacuum environment of the lunar surface. It is necessary to establish a ground test device to simulate the vacuum thermal environment of the lunar surface to test the performance of the sample in vacuum thermal environment. Therefore, the degree of vacuum is required and it can achieve precise control. In this article, a technical scheme for accurate vacuum control using FC series proportional flow control valve is proposed for the ground simulation test device of vacuum thermal environment. 1. Question In the lunar exploration project, it is necessary to collect lunar soil samples in the vacuum environment of the lunar surface. Therefore, a ground test device needs to be established to simulate the vacuum thermal environment of the lunar surface to test the performance of sample in the vacuum thermal environment, and accurate vacuum control is required to reach precise control. Due to the particularity of the lunar soil, vacuum control in current lunar soil ground model test device still needs to solve the following problems: (1) Lunar soil and simulated lunar soil samples are generally powdery particles, so the pumping rate in the initial time should be strictly controlled to avoid dust generation. (2) The current vacuum measurement and control also uses a Pirani vacuum gauge, which makes the matching control system unable to reach precise control of the vacuum, resulting in poor repeatability of the test results. (3) The lunar soil ground simulation test device is generally small in size, and it has always been difficult to achieve precise control within a wide range of vacuum degrees. The fluctuation of vacuum degree is large, which is also one of the reasons for the poor repeatability of test results. Aiming at the above problems existing in the lunar soil ground model test device, this article focuses on corresponding technical solutions and introduces the detailed implementation process. 2. Technical Scheme The overall structure of vacuum density control system of lunar soil environment ground simulation test equipment is shown in Figure 1. The whole system mainly includes a vacuum gauge, two proportional flow control valve, a PID controller and a vacuum pump. In order to do the precise control of the full range of vacuum degree, three capacitance vacuum gauges are generally required, and the measurement accuracy of vacuum gauge is 0.25%. In order to match the measurement accuracy of capacitance vacuum gauge, the controller adopts a high-precision PID controller with 24-bit A/D and 16-bit D/A, and the independent dual-channel facilitates the gas flow adjustment and control of the upstream proportional flow control valve and downstream proportional flow control valve control. The precise control of vacuum degree uses dynamic control mode, that is, the downstream proportional flow control valve is adjusted under low vacuum conditions, and the upstream proportional flow control valve is adjusted under high vacuum conditions. This is a typical forward and reverse control method, which can effectively ensure the control accuracy of vacuum degree. In conclusion, with this proven accurate vacuum control scheme, a control accuracy of better than 1% vacuum over the full scale range can be achieved. For further information on different models of proportional flow control valve, please visit https://www.genndih.com/proportional-flow-control-valve.htm