The Mechanism Research And Inhibition Methods Of IFOG Dead Zone

Since the error of IFOG output is large when the input rotation rate is low,it is difficult to meet the satellite,and other areas of the application of high measurement precision.(1)Firstly,it analyzed the detector's errors in main circuit.Then from this,it analyzed the effects of the feedback-loop nonlinearity errors and the electrical cross-coupling performances of closed-loop FOG when the input rotation rate is low,in which the error sources include the electrical cross-coupling,the non-linearity of integrated-optic chip and the non-linearity of digital-to-analog converter.And it is shown that the integral nonlinearity of feedback loop can be eliminated when the input rotation rate is higher than the equivalent rotation rate of integral nonlinearity.(2)Otherwise,the linearity error can cause a dead zone.The simulation and experiment results prove the above conclusion.(3)Finally,a series of methods was given to improve dead zone.The first technique is the dithering technique,which shifts the modulation phase and prevents it from getting locked at one constant level.The second technique is the modifying the modulator circuit boards to reduce the electronic cross coupling between the circuit.The second,a six-state modulation(SSM)technique has present to reduce crosstalk.Compared to conventional four-state modulation(FSM),the SSM reduces the correlation between modulation voltage and demodulation reference by separating their fundamental frequencies,and thus reduces the bias error induced by crosstalk.In addition,improving the AD sampling frequency,making the modulation frequency as far as possible consistent with the intrinsic frequency and random modulation and so on all can effectively suppress dead zone.The measured dead band of a 1000-m and 100-mm of diameter IFOG is reduced from the original 0.1°/h to 0.05°/h through redesigning circuit board.It is also verified that the dead zone of FOG can be effectively reduced when the modulation frequency is consistent with the eigenfrequency.By testing,The measured dead band of the IFOG is approximately 0.05 °/h using FSM and approximately 0.01 °/h using FSM with triangle wave dithering,also approximately 0.03 °/h using SSW,whereas there is no evidence of dead band using SSM in theory.The IFOG using SSM also exhibits better angular random walk(ARW)and bias instability performance compared to the same IFOG using FSM or SWM.These results verify the crosstalk reduction effect of FSM with triangle wave dithering and SSM.