DC resistance measurement circuit

When the transfer switch is placed in the resistance measurement position, its circuit composition
is as shown in the figure. The ohmic range of the 500-type multimeter uses
a voltage-dividing zero-adjusting resistor. The ohmic
center values ​​of each range from ×1 to ×lOk are iori, ioon, lktl, lOkn, and
lOOkil respectively. For example, in ×l gear, the ohmic shunt resistance is 9.4n, plus
the internal resistance of the battery is about 1n. And considering the parallel connection with other circuits
, the effective internal resistance of this gear is 10S1. Therefore the center ohms
value is also 100.
    ×iok high-resistance gear, the battery voltage is 1-5V-1-9V,
and the shunt resistor is removed, and an 85.2kfl
resistor is connected in series, so the central resistance is 100kfl.
    It can be seen from the above analysis that as the ohmic range
increases, in order to prevent the sensitivity of the meter from being affected,
dual measures are taken to increase the battery voltage and line sensitivity.