5.8.2 Locating Problems Using Loop Check Tool
When a problem is encountered during testing with input/output equipment
connected to an I/O module, the first thing to do is to check the values of the I/O
modules.
● If Values are Displayed in Loop Check Tool
If values are displayed in Loop Check Tool but the actual input/output values are
different from the values of a device label variable, there are three possible cases.
Case 1: Loop Check Tool and device label variable have the same values,
which are different from the value of process I/O
Given that Loop Check Tool and device label variable have the same values, we
can see from the figure shown in Section 5.8.1, “Values Displayed in Loop Check
Tool” that there is no problem from the CPU module up to A/D conversion or D/A
conversion by the I/O module.
Thus, the problem lies not on the application side but on the I/O equipment side
from A/D conversion or D/A conversion to the I/O equipment. In this case, check
the connection between the I/O module and the equipment, and check the
hardware settings.
Case 2: Loop Check Tool and process I/O have the same values, which are
different from the values of the device label variable
Given that Loop Check Tool and process I/O have the same values, see from the
figure shown in Section 5.8.1, “Values Displayed in Loop Check Tool” that there
is no problem from the I/O equipment up to A/D conversion or D/A conversion of
the electrical I/O signals by the I/O module.
Thus, the problem lies not on the hardware side but on the application side after
conversion. In this case, check Resource Configurator settings, Logic Designer’s
device label variable definitions and other aspects on the application side.
Case 3: Loop Check Tool, device label variable and process I/O all have
different values
This means that there may be problems in application definitions and settings, as
well as hardware connections and settings.
Firstly, check the connections and settings on the hardware side, and after
successfully making the Loop Check Tool and process I/O display the same
values as described in case 2 above, check the definitions and settings on the
application side.
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