Programming the Local Host
Chapter 5
539
Figure 5.24
Typical UserProgrammed Timeout
032
12
/
Remote Fault
TON
060
0.1
032
12
Start
010
02
060
15
Timed Bit
Indicator
Output
032
02
/
Done
PR 100
AC 000
033
02
/
Local Fault
In the first rung of this figure, Timer 060 times the interval between the
setting of the start bit for a command and the done, local fault, or remote
fault response of the PLC-2/DHII interface. If no response is received
within the preset interval of this timer, here 10 seconds, a fault may be
indicated and Bit 06015 is set ON. The second rung examines this bit to
turn on an annunciator. Depending on the individual application, you
could also use this bit to enable or disable various parts of the program.
The preset value of this programmed TON instruction is not critical. For
this type of backup monitoring, the programmed preset must exceed the
timeout preset interval entered as a code in the header rung. (Remember
that the automatic timeout of the PLC-2/DHII interface gives a local fault
response to a command which would indicate normal interface/host
communication, but faulted communication with some other node.)
As with automatic timeout preset monitoring, a user-programmed timeout
is useful as a backup to the other monitoring functions of the PLC-2/DHII
interface. Remote and local fault bits at other nodes indicate the same
types of faults that can be detected using a user-programmed timeout. A
programmed timeout would not be necessary for each command from a
node. Instead, you can monitor a single command at each node in this
manner. For this type of monitoring, select a command that is sent
regularly.
