Page 307 - Programmable Logic Controllers, Fifth Edition - Mobile version

associated wiring operate according to specifications. Be-
AC or DC the PLC, the ladder logic program, the I/O devices, and all
output module fore commissioning any control system, you should have
MOV
VAC/VDC +DC or L1 a good understanding of how the control system operates
OUT 0 and how the various components interact. The following
OUT 1 are general steps to be followed when commissioning a
OUT 2 PLC system:
OUT 3
Inductive load
OUT 4 • Before applying power to the PLC or the input
OUT 5 devices, disconnect or otherwise isolate any output
OUT 6 device that could potentially cause damage or injury.
OUT 7 Typically this precaution would pertain to outputs that
COM
DC Com or L2 cause movement such as starting a motor or operating
a valve.
Figure 13-13 Metal oxide varistor (MOV) surge
suppressor. • Apply power to the PLC and input devices. Measure
the voltage to verify that rated voltage is being
applied.
diodes connected back-to-back. The operation of an MOV
can be summarized as follows: • Examine the PLC’s status indicator lights. If power
is properly applied, the power indicator should be
• The device acts as an open circuit until the volt- on, and there should be no fault indication. If the
age across it in either direction exceeds its rated PLC does not power up properly, it may be faulty.
value. PLCs rarely fail, but if they do fail, it usually
• Any greater voltage peak instantly makes the device happens immediately upon powering up.
act like a short circuit that bypasses this voltage • Verify that you have communication with the PLC
away from the rest of the circuit. via the programming device that is running the PLC
programming software.
13.6 Program Editing • Place the PLC in a mode that prevents it from
and Commissioning energizing its output circuits. Depending on the
make of the PLC, this mode may be called disable,
After you have entered the rungs for your program, you continuous test, or single-scan mode. This mode
may need to modify them. Editing is simply the ability to will allow you to monitor input devices, execute
make changes to an existing program through a variety of the program, and update the output image file while
editing functions. Using the editing function, instructions keeping the output circuits de-energized.
and rungs can be added or deleted; addresses, data, and
bits can be changed. Again, the editing format varies with • Manually activate each input device, one at a
different manufacturers and PLC models. time, to verify that the PLC’s input status lights
Today, most PLC programming software is Microsoft turn on and off as expected. Monitor the associ-
Windows based, so if you are familiar with Windows and ated condition instruction to verify that the input
know how to point and click with a mouse, you should device corresponds to the correct program address
have no problem editing a program. In general, both in- and that the instruction turns true or false as
structions and rungs are selected simply by clicking on expected.
them with the left mouse button. Double clicking with the • Manually test each output. One way you can do this
left mouse button allows you to edit an instruction’s ad- is by applying power to the terminal where the out-
dress, whereas right clicking displays a pop-up menu of put device is wired. This test will check the output
related editing commands. If you want to include addi- field device and its associated wiring.
tional explanation of a symbol or address, you can place • After verifying all inputs, outputs, and program ad-
an address description on your ladder rung directly above dresses, verify all preset values for counters, timers,
the symbol. To add a page or rung comment, right click and so on.
on the rung number to which you wish to add the page or • Reconnect any output devices that may have been
rung comment. disconnected and place the PLC in the run mode.
Preparing a control process for start-up, also called Test the operation of all emergency stop buttons and
commissioning, involves a series of tests to ensure that the total system operation.

288 Chapter 13 PLC Installation Practices, Editing, and Troubleshooting

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