Integrating Type DVM (Voltage to Frequency Conversion):

The principle of operation of an Integrating Type DVM is illustrated in Fig. 5.5.

A constant input voltage is integrated and the slope of the output ramp is proportional to the input voltage. When the output reaches a certain value, it is discharged to 0 and another cycle begins. The fre­quency of the output waveform is proportional to the input voltage. The block diagram is illustrated in Fig. 5.6.

The input voltage produces a charging current, e_i/R₁ that charges the capacitor ‘C’ to the reference voltage e_r. When e_r is reached, the comparator changes state, so as to trigger the precision pulse generator. The pulse generator produces a pulse of precision charge content that rapidly discharges the capaci­tor. The rate of charging and discharging produces a signal frequency that is directly proportional to e_i.

The voltage-frequency conversion can be considered to be a dual slope method, as shown in Fig. 5.7.

Referring to Eq. 5.3 we have

But in this case e_r and t₂ are constants.

Let

The output frequency is proportional to the input voltage e_i. This DVM has the disadvantage that it requires excellent characteristics in linearity of the ramp. The ac noise and supply noise are averaged out.