
42-21Frequency Measurement
should be connected to the FC’s external time base input. Frequency accuracy can be estimated by using
Eq
uation
42.1, wh
ere
f
meas
is the reading taken from the FC display. e smallest frequency oset that an
FC ca
n
de
tect
wi
th
a si
ngle
re
ading
wi
ll
be de
termined
by it
s
re
solution,
wh
ich
is li
mited
by th
e
nu
mber
of di
gits
on th
e
co
unter’s
dis
play
. Fo
r
ex
ample,
a 10
-digit
FC wi
ll
be una
ble
to de
tect
a fr
equency
cha
nge
sma
ller
tha
n
1 × 10
−9
without averaging when measuring a 10 MHz signal, but a 12-digit counter can
re
duce
th
is
va
lue
by tw
o
or
ders
of mag
nitude
to 1 × 10
−11
.
TI
Cs
ar
e
co
mmonly
us
ed
to me
asure
fr
equency