Digital Transducers
Digital Frequency meter
• The signal waveform is converted into a train of pulses, one pulse for
each cycle of the signal
• The number of pulses occurring in a definite interval of time is then
counted by an electronic counter
Digital Frequency meter
• The signal may be amplified before being applied to the Schmitt
trigger.
• The Schmitt trigger converts the input signal into a square wave –
the output from the Schmitt trigger is a train of pulses, one pulse
for each cycle of the signal.
• The output pulses from the Schmitt trigger are fed to a START/STOP
gate
• When this gate is enabled, the input pulses pass through this gate
and are fed directly to the electronic counter, which counts the
number of pulses.
• When this gate is disabled, the counter stops counting the
incoming pulses.
Digital Frequency meter
Digital Frequency meter
• The input signal is amplified and converted to a square wave by a Schmitt trigger
• The square wave is differentiated and clipped to produce a train of pulses, each
pulse separated by the period of the input signal
• The time base selector output is obtained from an oscillator and is similarly
converted into positive pulses.
• The first pulse activates the gate control F/F. This gate control FF provides an enable
signal to the AND gate.
• The trigger pulses of the input signal are allowed to pass through the gate for a
selected time period and counted.
• The second pulse from the decade frequency divider changes the state of the
control FF and removes the enable signal from the AND gate, thereby closing it.
• The decimal counter and display unit output corresponds to the number of input
pulses received during a precise time interval
Digital Tachometer
• The selection of the gate period is in accordance with the rpm
calibration
Digital Tachometer
• The rpm of a rotating shaft is R
• Let P be the number of pulses produced by the pick up for one revolution
of the shaft.
• In one minute the number of pulses from the pick up is R x P.
• The frequency of the signal from the pick up is (R x P)/60
• Now, if the gate period is G s the pulses counted are (R x P x G)/60.
• In order to get the direct reading in rpm, the number of pulses to be
counted by the counter is R, select the gate period as 60/ P, and the
counter counts
