Technical data

Manual VIPA System 200V Chapter 3 Digital input modules
HB97E - SM - Rev. 09/19 3-39
In frequency measurement mode, the module counts the number of rising
edges of channel A received within a specified time window.
Channel B is not used in this mode.
The time window T
W
is specified indirectly by selecting a reference fre-
quency with DO byte 5 and defining a load value in DO bytes 0 to 3:
ValueLoadT
W
∗=
Frequency Reference
1
By setting the Bit 2 of the control byte, the time window is transferred.
When the counter is enabled (software gate is open), the reference counter
is started with the first rising edge of channel A and is incremented with
every rising edge of the reference clock.
When the reference counter reaches the load value (time T
W
has expired),
the current counter value is copied to DI byte 0 to 3 and can be read.
Then the counter and the reference counter are cleared automatically and
the next frequency measurement is started with the next rising edge of
channel A. If there aren’t at least two rising edges of channel A within the
time window T
W
, the counter value will be read as 0 for this measurement.
Frequency measurement is started and ended by using the software gate
that is as long as the software gate is open, the frequency of channel A is
measured.
The counter can be cleared at any time by CLEAR=’1’ in the control byte
while the load value stays valid until a new value is loaded or a Reset is
detected.
The recent frequency can be computed by using the following formula:
ValueLoad
ValueCounter
Frequency ∗= Frequency Reference
Signal A
SW-Gate
Counter
Reference Counter
DI Data
next measurementTw
012
m
01
001234567
n
0 12345
m
0
Example:
Reference Frequency : 1 MHz
Load Value (n) : 1.000.000
Counter Value (m) : 10.000
kHzMHzFrequency 10
000.000.1
000.10
1 =∗=
Frequency
measurement
(03h)