Development On Non-rotating Piston Gauge And Its Control System

The aim of pressure measurement is to ensure that pressure measuringinstruments can get accurately pressure value, applied in pressure measurement field,piston gauge is a standard pressure metrological verification instrument of highaccuracy, high repetition and high degree of confidence, also used as necessarystandard of the pressure value calibration, verification and dissemination. Itsfunction is based on Pascal’s law and the Fluid static theory, and it is consist ofvalidator,special weight and piston system. The machine uses the balance of weightgravity and the force of liquid on the piston to test pressure, and regulates thepressure through the validator. However, conventional piston gauge still has someaspects to improve, such as: low automatization, the effect of the mechanical frictionof piston system, the step of putting the weight into rotation state, these factors makethe control of piston gauge difficult and measurement accuracy low, also lead tomore error accumulation, putting negtive effects to scientific research, productionand measurement work.This topic is derived from the project cooperated with Jilin Scientific MetrologyInstitute “10MPa non-rotating piston gauge”, and the purpose is to improve theverification precision, automation level and the efficiency of the standard device ofpressure measurement, so we develope a new type rotationfree piston gauge. Inthis paper I have designed the structure and principle of the equipment, and focusedon the development of the control system.The non-rotating piston gauge is also based on Pascal’s law and the Fluid statictheory, uses the balance of weight gravity and the force of liquid on the piston to testpressure, but it adopts piston system with rolling friction, the pattern of laodingweights respectively and the servo pressure calibration. The piston and the pistoncylinder contact at rolling points, throngh which we can change the sliding frictioninto rolling friction, so the effect of friction on precision is lowered. Also in this waycan we ignore the rolling of weights and simplify the manufacturing process of thepiston system. We act the weigh on the piston through the hanging organization,inwhich way we can improve the execution stability, and the use of laoding weightsrespectively makes combination in any form possible. The drive is formed by a cammechanism driven by a motor, driving the weights move along the guide rail vertically, and we use approach switch to control the displacement. We use servomotor to make the plunger type cylinder work and use displacement sensor tocontrol the position. The sensor gives the signal to processing unit，when thepressure is unstable，the PC controls servo system by the singal to fill oil for cylinderthrough adjusting piston moving velocity. By adjusting the servo pressure calibrationcan we make the calibration of the pressure automatically and make the result moreaccurate and reliable.The control system developed in this subject is based on "PC+control card"mode, the hardware is determined according to the function of the equipment andthe compatibility of the components, and the control software is developed inaccordance with the execution flow and control demand of the equipment. Thehardware system includes: computing unit, data acquisition unit, the power sourceand other electrical components, I have introduced the main parameters of thehardware, the design of the electrical connection is from two aspects of the weightloading unit and pressure calibration unit. The control software is developed basingon Windows platform, using VC++as a developing tool. I have designed a moreintuitive and visualizer Man-machine interface. The main aim is to control theproduction and release of the standard pressure value, the scheduling of the modules,the process of experimental data, the track of the state and the detection andprocessof unexpected event.At last, I will demonstrate the feasibility of the control system through thetesting experiment of pressure sensor, tacing the information interaction state of thecontrol software, I have demonstrated that non-rotating piston can work according tothe Verification Regulation of pressure measurement instrument, which meet withthe Measurement standard.