• This time interval is measured with an electronic time interval counter and the count is displayed as a number of digits on electronic indicating tubes of the output readout of the voltmeter.
• The conversion of a voltage value of a time interval is shown in the timing diagram of Fig.
• At the start of measurement a ramp voltage is initiated.
• A negative going ramp is shown in Fig. but a positive going ramp may also be used.
• The ramp voltage value is continuously compared with the voltage being measured (unknown voltage).
• At the instant the value of ramp voltage is equal to that of unknown voltage.
• The ramp voltage continues to decrease till it reaches ground level (zero voltage).
• At this instant another comparator called ground comparator generates. a pulse and closes the gate.
• The time elapsed between opening and closing of the gate is t as indicated in Fig.
• During this time interval pulses from a clock pulse generator pass through the gate and are counted and displayed.
• The decimal number as indicated by the readout is a measure of the value of input voltage.
• The sample rate multivibrator determines the rate at which the measurement cycles are initiated.
• The sample rate circuit provides an initiating pulse for the ramp generator to start its next ramp voltage.
• At the same time it sends a pulse to the counters which set all of them to 0.
• This momentarily removes the digital display of the readout.
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