Page 499 - Instrumentation Reference Book 3E

482 Electrical measurements

+
L i
-!v
N lnputand - Input cycle
-+ trigger + counter I I
circuitry - ni
Lt. Synchronizing - A +
-
network and Microprocessor
+ maingate +
7 b +
I
10 MHz - A Timer I '
crystal counter
oscillator nOSC Measuring
time

Gating Gating period t equivalent
period ts to nOIC counts %f IO MZ
a
Number of cycles counted ni
Counted with an uncertainty
cycles IIII corresponding to tl count
of input
waveform
n.
Measured frequency fi =
noSc. io-'
t1
Relative resolution = -
"i
Conventional frequency counter

Input
frequency F
to ni counts of hput frequency
Gating
Number of cycles counted nosc
period 1, 's - I with an uncertainty
corresponding to il count
Counted
cycles of
10 MHz
Measured frequency fi =-'kc,
oscillator
n.
- 10-7
1
Relative resolution = k -
nOSC
Reciprocal frequency counter
Figure 20.75 Digital frequency counter.