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Model 5328A
Operation
3-6
CASE
NO. 1
CASE
NO. 2
SIGNAL
INPUT
| |
| |
| |
| |
| |
| |
TO MAIN
GATE
|
{
t
t
4
t
1
i
i
{
1
I
ee
ee
aa
GATE
OPENING
SIGNAL
COUNTED ——
|
ILL
Figure 3-6.
+1 Count Ambiguity
NOTE
The main gate is open for the same time tm, in both
cases. Incoherence between the clock and the input
signal can result in two different counts which for this
example are 1 for case No. 1 and 2 for case No. 2.
3-38.
FREQUENCY MEASUREMENT ERROR. The error caused by the ambiguity is in absolute
terms, +1 of the accumulated count.
For a frequency measurement the signal counted is the
input signal of frequency fj,. Thus the relative error is given by
+1 count error, relative frequency measurement error
Af _ +1
(2)
3-39.
PERIOD MEASUREMENT ERROR. For period measurement, on the other hand, the signal
counted is the internal time base clock of period tc. Hence the relative error becomes
+1 count error; relative period measurement error
AT
+t
3)
T
Tin
3-40.
MAIN GATE REQUIREMENTS. The +1 count error described above assumes the main gate
itself does not contribute any error.
As with any gate, however, the main gate does exhibit
propagation delays and takes finite times to both switch on and off. Any differential between the
times taken for the main gate to switch on and off show up as uncertainties in the length of time
the gate isopen. This uncertainty in turn translates into a measurement error that increases the +1
count. However, the uncertainty in the main gate of the 5328A is substantially less than the period
of the highest frequency counted, so this error is not appreciable.
3-41.
Time Base Error
3-42,
Any error in the time base oscillator directly translates itself into a measurement error.
Thus, if the total of all the oscillator errors amount to 1 x 10°, the total error contributed by the
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