Ectron 441A, Instructions Manual, Page: 40 / 74

changes the analog output to that shown by the smoothed
trace. Note that the second cycle of eight steps is changed
to a steady 5.0 V level. When the frequency abruptly
changes to the 5.4 V level, the digitally-averaged signal
linearly changes so that in eight steps, the 5.4 V level
is reached. As a result of the digital filter, the variation
(noise) caused by the eight-step cycle is eliminated. Dur-
ing and after the transition to a new level, eight-step
averaging continues.
The stair-step wave form during the frequency change
in Figure 4-6 is a result of the update rate of the unit,
which when period averaging is allowed, is longer than
1 ms. That is, period averaging only works below 1 kHz.
The filtering effect of digital averaging is useful in re-
ducing random noise signals as well as periodic signals.
Response time will be reduced in direct proportion to
the Sample Count setting although response time will
change with input frequency. For example, for an eight-
count sample period and an input frequency of 64 Hz
the response time (to reach final value) will be
1
⁄
8
s.
For a frequency of 6400 Hz the response time will be
1
⁄
800
s.
Figure 4-6
Effects of the Digital (Periodic-error) Filter
Applications Model 441A
4-10