Page 322 - Programmable Logic Controllers, Fifth Edition - Mobile version

4. During the static checkout of a PLC system, a
specific output is forced on by the programming f. How could you tell by observing the program-
ming device monitor if the limit switch was
device. If an indicator other than the expected one stuck closed?
turns on, what is the probable problem? 11. Assume that prior to putting a PLC system into op-
5. The input device to a module is activated, but the eration, you want to verify that each input device is
LED status indicator does not come on. A check connected to the correct input terminal and that the
of the voltage to the input module indicates that no input module or point is functioning properly. Out-
voltage is present. Suggest two possible causes of line a method of carrying out this test.
the problem. 12. Assume that prior to putting a PLC system
6. An output is forced on. The module logic light into operation, you want to verify that each
comes on, but the field device does not work. output device is connected to the correct output
A check of the voltage on the output module terminal and that the output module or point
indicates the proper voltage level. Suggest two is functioning properly. Outline a method of
possible causes of the problem. carrying out this test.
7. A specific output is forced on, but the LED module 13. With reference to the ladder logic program of
indicator does not come on. A check of the voltage Figure 13-38, add instructions to modify the
at the output module indicates a voltage far below program to ensure that the second pump_2
the normal on level. What is the first thing to does not run while pump_1 is running. If this
check? condition occurs, the program should suspend
8. An electronic-based input sensor is wired to operation and enter code identification number
a high-impedance PLC input and is falsely 100 into S2:7.
activating the input. How can this problem be 14. The program of Figure 13-39 is supposed to
corrected? execute to sequentially turn PL1 off for 5 seconds
9. An LED logic indicator is illuminated, and and on for 10 seconds whenever input A is
according to the programming device monitor, closed.
the processor is not recognizing the input. a. Examine the ladder logic and describe how the
If a replacement module does not eliminate circuit would operate as programmed.
the problem, what two other items should be b. Troubleshoot the program and identify what
suspected? needs to be changed to have it operate properly.
10. a. A normally open field limit switch examined for
an on state normally cycles from on to off five Inputs Ladder logic program Outputs
times during one machine cycle. How could you L1 L2
tell by observing the LED status light that the PB1 Pump 1
limit switch is functioning properly?
b. How could you tell by observing the program- PB1 Pump 1 M1
ming device monitor that the limit switch is Pump 1
functioning properly? PL1
c. How could you tell by observing the LED status PL1
light whether the limit switch was stuck open? PB2
d. How could you tell by observing the program- PB2 Pump 2 Pump 2 M2
ming device monitor whether the limit switch
was stuck open?
e. How could you tell by observing the LED status
light if the limit switch was stuck closed? Figure 13-38 Program for Problem 13.

PLC Installation Practices, Editing, and Troubleshooting Chapter 13 303

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