This circuit will provide an indication whenever the input voltage differs from two defined limits, V1 and V2. The supply voltage, Vcc must be higher than the highest input voltage by at least 2 volts. One application here is to monitor a 12V car battery. V1 could be set to 14V and V2 to 11V thus giving an indication of over charge or a weak battery.
The op-amps used here are MOSFET CA3140. They are used to advantage as they have very little output offset voltage and can switch down to near 0volts. If any other op-amp is used such as LF351 or CA741 then it will be necessary to have an offset null cont