| Refrigeration system has been widely used in all aspects of human life,wherein the vapor compression refrigeration system has been very popular.The refrigeration system has many parameters,so it is complex to maintenance,and difficult to assess.Traditionally,in order to debug and maintain the refrigeration system,technicians in the field need to carry many tools to record data manually,and to query a variety of information results in high costs to diagnose fault and maintain the refrigeration system.The commonly-used pressure gauge group does not give substantial help to field technicians yet.Therefore,it is necessary to develop a professional instrument to meet the urgent need for measurement and analysis of refrigeration system.By analyzing the characteristics of existing refrigeration measuring meter and studying the principles of a vapor compression refrigeration cycle,this paper presents the design of refrigeration system comprehensive test instrument.The important issues on data processing,low power consumption and anti-jamming were studied in this paper.The meter uses two temperature sensors and two pressure sensors to measure four parameters of refrigeration system including superheat temperature,subcooling temperature,evaporating pressure,condensing pressure respectively.Combined with built-in saturated steam tables/pressure-enthalpy diagram,and the thermodynamic equation,the refrigeration system performance parameters and thermodynamic parameters can be obtained easily.In order to improve the accuracy of the sampling data and precision of the measurement results,the data processing is divided into four stages,including zero drift suppression,filtering,temperature compensation and calibration.The corresponding data processing scheme is designed for each stage.A simple but efficient baseline-slope method is used in the zero drift suppression stage.In the filtering stage,the frequency domain and time domain characteristics of the data are analyzed;for frequency filtering,a first order inertial filter is designed by simulating the hardware RC filter;for time-domain filtering,the kalman filter is designed;finally series with two filters for data filtering.In the temperature compensation stage,the three methods of two-dimensional interpolation,one-dimensional interpolation and surface fitting are compared,then the optimal one,surface fitting method is selected.In the calibration stage,the calibration line is obtained through the tests,and the results can be further modified by this line.Low power design of the instrument is carried out.The design takes many respects such as,device selection,the device itself low-power modes and low power consumption control strategy and so on into consider.A variety of low-power modes of controller chip are taken advantage bypower management.Anti-jamming design of the instrument is carried out also.Focused on the interference coupling,an effective mean of cutting off its coupling is used to achieve the purpose of suppressing interference.In addition,the suppression schemes of three common transient interference,electrostatic discharge,surge and electrical fast transient burst,were proposed.Refrigeration system comprehensive test instrument is an integrated instrument that expands the variety of functions of instrument in the refrigeration field,such as performance testing,thermodynamic properties measuring,leak detecting,vacuumizing and refrigerant charging.It is suitable for air-conditioning cooling,heating and automatic modes.When using for measuring single refrigerant refrigeration system,it can support up to 64 different refrigerants.It can complete firmware updating,refrigerant data downloading,recorded data online uploading and real-time monitoring by USB interface.the full-scale error of pressure is ±0.3%,and indication error of temperature is ±0.3?.The development of the instrument improves the intelligence level of refrigeration measuring instruments,and brings convenience to the scientific research and maintenance of refrigeration system. |
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