Iwatsu SC7101 - Page 18

SC-7101/SC-7102
Section 3 Measuring Procedures
Errors
in
Measurement
When
average
values
of
input
signals
during
Fi
:
-
Errors
in
frequency
measurements,
there
are
N
period
are
measured:
igure
3-3-2.
Frequency
and
Error
in
Frequency
Measurement
I
errors
due
to
accuracy
of
the
reference
oscil-
2a
1
En
1
(Sinewave;
when
S/N
is 40
dB)
(SC-7101)
lator",
"+
1
count
error"
and
the
"Trigger
error".
NT
7
*
es
*
Ww
.
Showing
1/N
reduction
in
error.
Consequently,
Error
due
to
accuracy
of
the
reference
oscil-
measurements
of
average
values
of
various
periods
My
lator":
are
advantageous
as
they
can
reduce
influence
Since
the
counting
time
(gate
time)
of
the
of
noise.
+
10
MHz
or
more
frequency
measurement
are
determined
by
dividing
1
kH2/1
ms,
10
H2/O.1
sy
1
Hz/1
5,
O61
Hz/10
s
the
oscillation
frequency
of
the
reference
oscil-
How
do
these
errors
appear
in
the
actual
mea-
10
fie
on
Less:
lator
(crystal
oscillator),
this
error
depends
surement.
Figure
3-3-2
and
3-3-3
shous
relation
‘an
aah
ria
tack
aca
shee
on
the
accuracy
of
the
reference
oscillator.
between
input
signal
and
error
frequency
after
cee
calibration
of
the
reference
oscillator
and
[
"Error of + 1 count": errors.
Although the digital measuring instrument is
a
measuring
instrument
of
high
accuracy,
on
in-
Figure
3-3-1.
Trigger
Error
[
struments which count by opening and closing
of gates, a quantization error of + 1 count oc-
curs.
Limit due to accuracy of the internal
reference oscillator
Noiseless
Es signal
"Trigger Error":
Normally the measuring error due to the trigger
error is proportional to the noise level. This
error
is
larger
when
the
slope
of
the
area
set-
———1
period
4
eale
ting the trigger level of the input signal wave-
form is less sharper.
This error is the minimum when the trigger
level of a sine waveform, as shown in Figure
3-3-1, is set in the center level of the waveform.
Relation of the input signal voltage, noise volt-
age and the error can be expressed by the follow-
ing equation.
2aT 1, £0 (..fn 27s,
Teo Es at” TT
A i
H H
H H
1 .
Signals with noise
Figure 3-3-3. Frequency and Error in frequency Measurement II
(Sinewave; when S/N is 40 dB) (SC-7102)
Maximum period -——|
10 MHz or more
| 1 kHz/1 ms, 10 Hz/0.1 s, 1 H2/1 s, 0.1 Hz/10 s
10 Mz or less
4 digits/1 ms, 6 digits/0.1 s, 7 digits/ 1 s,
8 digits/ 10 s
As it is clear from this equation, in case
of the sinewave, this error is solely determined
by the ratio of noiseless signal Es and noise
En, irrespective of the frequency. For example,
the error when S/N is 40 dB, comes to 0.3 % when ghee
60 cB, 0.03 % from the above equation.
Limit due to accuracy of the internal
reference oscillator.
OOMHE
OH: 100Hz~=—«sTkHz ~=—«10kHz_-—=«100kHz»=« MHz © 10MHe
200MHz