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 digital frequency meter working principle pdf

digital frequency meter working principle pdf
The digital multimeter is an instrument that is capable of measuring a.c. voltages, d.c. voltages, a.c. and d.c. currents and resistances in several ranges. The basic circuit of a digital multimeter is always a d.c. voltmeter. The digital frequency meter is a general purpose instrument that shows the frequency of a periodic electrical signal with an accuracy of three decimals. Counts the number of events that occur within the oscillations during a given time interval. As the preset period is completed, the value in the counter is displayed on the screen and the counter is reset to zero. There are several types of instruments available that operate at a fixed or variable frequency. But if any frequency meter operates at a different frequency than the specified range, it could be carried out abnormally. To measure low frequencies, deflection type meters are widely used. The deviation of the pointer on the scale shows the change in frequency. The instruments of the type of deflection are of two types: one is electrically resonant circuits and another is the ratio meter.

Principle of operation of the digital frequency meter

A frequency meter has a small device that converts the sinusoidal voltage of the frequency into a train of unidirectional pulses. The frequency of the input signal is the displayed count, averaged over an appropriate count interval of 0.1, 1.0 or 10 seconds. These three intervals are repeated sequentially. As units are reset count rings, these pulses pass through gate time base and then enter the main gate, which is opened for a certain period of time interval.

The time base gate prevents a splitter pulse from opening the main gate during the display time interval. The main door acts as a switch when the door is open, the pulses can pass. When the gate is closed, the pulses can not pass, which means that the flow of pulses is obstructed. The operation of the door is operated by the flip-flop of the main door. An electronic counter at the exit of the door that counts the number of pulses passed through the door while it was open. As the next divider pulse is received on the flip-flop of the main door, the counting interval ends and the pulses of the divider are blocked. The resulting value is displayed on a display screen having units of counting rings scale of ten circuits and each unit is coupled to a numeric indicator, which provides the digital display. As the reset pulse generator is activated, the ring counters are automatically reset and the same procedure starts again.
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