Research And Design Of Capacitive Grating Altimeter

As a kind of high accuracy and long displacement measuring transducer,Capacitive grating sensor was developed in 70-80 period of 20th century.Compared with other grid sensor,it has many merits lied in simple structure,small volume,low power,strong ability in resisting disturbance,better suitability,high accuracy and so on.It was extensively used in distancer,altimeter,electronic digital display calipers and stroke measurement of machine tools.Based on the research of phase demodulation Capacitive grating and amplitude discrimination Capacitive grating principle,the pumping style of signal and discipline of output signal in phase demodulation Capacitive grating sensor were investigated deeply. Then a capacitive Grating Altimeter of phase demodulation was designed through lots of experiment.STC89C52RC was the control nucleus of the designed capacitive grating altimeter. Intel8253,as a programmable counter,was the phase demodulation nucleus.Using digitize phase demodulation,output signal phase change caused by relative displacement of capacitive grating is converted to displacement.Pumping signal generating circuit of phase demodulation Capacitive grating and charge amplify circuit of output signal were detailedly introduced.D-Type Flip-Flop Array output 8 channels of square wave which had 45°phase separation.These signals were the pumping signal of the system.When capacitive grating was droved by pumping signals,it output charge signal at the same frequency of pumping signal.After amplified and shaped, phase demodulation operation can transform phase change into change of counting pulse numbers.Then digital displacement measure can be realized.Measured value was displayed with LED.The measuring range of Capacitive grating altimeter was from-100mm to 100mm,its resolving capability reached 0.00254mm(0.1mil),keyboard operation can initialize or clear displayed data.the displayed value can be transformed between Metric and Imperial synchronously.