Technical data

Chapter 3 Digital input modules Manual VIPA System 200V
3-40 HB97E - SM - Rev. 09/19
With very small frequencies, it is convenient to measure the period instead
of the frequency. In the operating mode "Period Measurement", the time
between two rising edges of channel A is measured by counting the
number of rising edges of the selected reference clock occurring between
two rising edges of channel A. Channel B is not used in this mode.
Period measurement is started and ended by using the software gate, that
is: as long as the software gate is open the period of channel A is
measured continuously. The counter can be cleared at any time by
CLEAR="1" in the control byte. The period measurement will then start
again with the next rising edge of channel A.
The recent signal period can be computed by using the following formula:
ValueCounterPeriod ∗=
Frequency Reference
1
Signal A
SW-Gate
Reference Counter
DI Data
next measurement
001234567
n0
0
12345
0
n
n
Example:
Reference Frequency : 1 MHz
Counter Value (n) : 10.000
msPeriod 10000.10
MHz1
1
=∗=
Note!
The counter value stays valid until the next measurement is completed or
the counter is cleared.
If the next measurement is never completed (e.g. because the second
rising edge of channel A never occurs), you will always see the "old"
counter value and not the current value of the Reference Counter.
Period
measurement
(04h)