Based on the current signal measurement project of an aerospace vehicle accelerometer

three methods are discussed for measurement of nA weak current in the range of 8 decuple（160 dB）:current-voltage（I-V）linear conversion measurement

current-frequency（I-F）conversion measurement

and current-voltage（I-V）logarithmic conversion measurement.The comparison model of I-F conversion and high AD conversion is built innovatively.The resolution transformation effect of I-V logarithmic conversion is proposed.The current-voltage（I-V）logarithmic conversion measurement method is used to make the 6-channel acquisition board card

which is proved by Beijing Oriental metrology and testing institute to be able to complete the current measurement within 160 dB and error less than 10 %.