Ohmmeter circuit

A multi-range ohmmeter. In this circuit, the operational amplifier is powered by a single power supply . The resistor R to be measured is connected across the feedback loop of the operational
  amplifier . The reference voltage VR EF is added to the non-inverting terminal to obtain
    J=VwtR/R1 (R,.+R2)
    ~1,
    it can be seen that the current j is proportional to the resistance being measured. Moreover, the meter head has a linear scale, and
  changing the resistance Ri can change the range of the ohmmeter.
    This ohmmeter does not require a zeroing mechanism because it measures short circuit (i.e. wind =
  0). The circuit becomes a voltage follower. Vo— VR EF, so the meter current is zero, realizing
  automatic zero adjustment.
    The voltage regulator tube plays the role of protecting the meter. If there is vs, when R exceeds the range
  , especially when R - oo, that is, when the measurement end is open circuit, the output voltage of the operational amplifier
  will be close to the power supply voltage. Overload the header. To this end, set vs to implement output clamping to
  prevent overloading of the meter.