VOLTAGE APPLICATION CURRENT MEASURING INSTRUMENT WITH AUTOMATIC CALIBRATING FUNCTION

摘要

PURPOSE:To decrease the number of standard current sources for calibration as much as possible and to calibrate a current measuring circuit in a short time by providing resistors for current detection so that resistance values are switched according to the value of a current which flows through a body to be inspected. CONSTITUTION:Changeover switches (SW) S6-S9, S10 and S12 which are brought under the individual switching control of a microcomputer 10 are provided. The SWs S6-S9 can connect one-end sides of the resistors R1-R5 for current detection from the output side the operational amplifier 32 of a voltage generator 30 to a common potential point 42 selectively and the resistors are usable as a current load when necessary. The SW10 is provided on the output side of an amplifier 32 and when a contact 1 is selected, the output voltage is supplied to each one-end side of a resistor. Consequently, the resistance value of one of the resistors and the gain of the differential amplifier 41 of a current measurement system are measured and known. The current measurement system which has the known gain based upon the resistance value of this resistor is utilized to measure the resistance value of a resistor R used in another current measurement range, so that each measurement range is calibrated according to the measurement result.