voltage prescaler

If one wants to measure a voltage which is greater than the range (full-scale deflection) of a meter, there are two things which can be done. On the one hand, the input voltage can be reduced to an acceptable value by employing a voltage divider. This is• tantamount to `compressing` the entire range of voltages to be measured. Alternatively we can arrange for the meter scale to cover only a certain portion of the total range of input voltages, depending upon the amplitude of the input signal. For example, with a voltage of 26 V, a 10 V meter will `look at` the 20 V -30 V range, and a reading of 6 V will be obtained. The circuit described here performs the function of `prescaling` a 10 V meter auto-matically, and can be used to measure input voltages between 0 and 30 V.