Mitsubishi Electric WS0-CPU0 - EDM (External Device Monitoring)

Chapter 9
162
Logic programming – Function blocks
9.8.7 EDM (External device monitoring)
Function block diagram
General description
The EDM (External device monitoring) function block allows to control an external
device (e.g. a contactor) and to check on the basis of its feedback signal whether it
has switched as expected. To this purpose the external device is connected to Output
1 and/or Output 2. The feedback signal is connected to the EDM feedback input. The
Monitored input is connected to the logic signal that represents the desired state for
the external device, e.g. the Enable output of a Reset function block.
Parameters of the function block
Parameter Possible values
Max. feedback delay
100 to 1,000 ms in 10 ms steps. The value has to be greater than
the logic execution time.
Use fault present  With
 Without
Use Error reset
Output 1 and Output 2
Both outputs have always the same value. This way, two outputs are available to
connect two output elements directly.
Output 1 and Output 2 become High, if the EDM feedback is High and the
Monitored input changes from Low to High subsequently.
Output 1 and Output 2 become Low, if the Monitored input is Low or if an EDM
error is present (EDM error output is High).
EDM error and Fault present
Generally it is expected that the EDM feedback input always takes the inverted value
of the Monitored input before the configured Max. feedback delay (T
EDM
) has
expired.
The EDM error and Fault present outputs become High, if …
 the Monitored input changes from Low to High and the EDM feedback input is
Low (irrespective of T
EDM
), or
 the Monitored input changes from Low to High and the EDM feedback input does
not change from High to Low before T
EDM
has expired, or
 the Monitored input changes from High to Low and the EDM feedback input does
not change from Low to High before T
EDM
has expired, or
 the Monitored input is Low and the EDM feedback input changes to Low for
longer than T
EDM
, or
 the Monitored input is High and the EDM feedback input changes to High for
longer than T
EDM
.
Figure 144:
Function block diagram for
the EDM function block
Table 69:
Parameters of the EDM
function block