Before installing a PLC system on-site, it's necessary to consider whether the installation environment meets the PLC's operating requirements. In this case, you can refer to the user manuals for various PLC products. This article introduces the precautions for on-site PLC installation.
Locations where PLCs cannot be installed: places containing corrosive gases, places exposed to direct sunlight, places where the temperature fluctuates rapidly in a short period of time, places where oil, water, or chemicals can easily penetrate, places with a lot of dust, and places with high vibration that could cause the mounting components to shift.
If the above-mentioned environments are unavoidable, a suitable control box must be constructed for the PLC, employing standardized specifications and necessary protective measures. If operation in extremely low outdoor temperatures is required, a control box with heating capabilities can be used. Manufacturers and qualified system integrators will provide the necessary supplies and designs for these protective boxes or control boxes.
When using a control box, the following points should be noted regarding the installation location of the PLC inside the control box:
Is the airflow inside the control box smooth (appropriate distance must be maintained between each device)? Are transformers, motor controllers, frequency converters, etc., kept at an appropriate distance from the PLC? Are power lines and signal control lines separated? Is the location of the components convenient for future maintenance? Is space reserved for future system expansion?
In addition to the above precautions, there are other things to keep in mind.
The most important thing is to isolate static electricity. Static electricity is an invisible killer, but because it doesn't pose a life-threatening danger, many people often ignore it. In northern China, in dry environments, static electricity on the human body is a factor that can damage electronic components. Although being shocked by static electricity might only cause a slight tingling sensation, it can be fatal to PLCs and any other electronic devices.
There are three ways to avoid static electricity shocks:
When repairing or replacing components, first touch a grounded metal object to remove static electricity from your body; do not touch connectors or IC pins on the circuit board; when electronic components are not in use, store them in anti-static packaging. Imagine the components inside the PLC as a delicate baby, and that static electricity could kill that baby; this will make it easier for you to approach the problem correctly.
When mounting the PLC on the base, after determining the positions of various control components and cable trays within the control box, mark the hole positions according to the dimensions shown in the drawings, drill the holes, and tighten the fixing screws until the base is secure. Before installing the power supply module, it is essential to check whether the grounding terminal on the power cord is connected to the metal casing; if not, it must be connected. Poor grounding can lead to a series of problems, such as static electricity, surges, and external interference. Because PLCs can often operate without grounding, many inexperienced engineers mistakenly believe that grounding is not so important. This is like climbing a mountain without a safety rope. While you are moving forward normally, the safety rope is useless, but if you slip and fall, without it, your life is over. Grounding the PLC is equivalent to attaching a safety rope to the PLC.
When installing I/O modules, the following points should be noted:
Before inserting the I/O module into the slot on the rack, you must first confirm that the module is the one you designed in advance.
When inserting the I/O module into the guide slot on the rack, make sure it is fully inserted to ensure that all contact points are tightly connected;
Make sure to tighten the module mounting screws; after inserting the terminal block, its upper and lower screws must be tightened. Due to the influence of transformers, motors, etc. on site, there will be some vibration. If these screws are loose, the module may come loose from the rack.
PLC installation
PLCs are suitable for most industrial environments, but they do have certain requirements regarding the operating conditions and ambient temperature. Controlling the PLC's working environment can effectively improve its efficiency and lifespan. When installing a PLC, avoid the following locations:
(1) The ambient temperature exceeds 0~50℃;
(2) The relative humidity exceeds 85% or there is dew condensation (caused by sudden temperature changes or other factors);
(3) Direct sunlight;
(4) Corrosive and flammable gases, such as hydrogen chloride and hydrogen sulfide;
(5) There are a lot of iron filings and dust;
(6) Frequent or continuous vibrations with a frequency of 10~55Hz and an amplitude of 0.5mm (peak-to-peak).
(7) Impact exceeding 10g (gravitational acceleration).
The small programmable controller has mounting holes at each of its four corners. There are two mounting methods: one is screw fixing, with different mounting dimensions for different units; the other is fixing via a DIN (German Republican Standard) rail. The DIN rail comes with a pair of mounting plates on each side. First, install the left and right plates on the rail, then install the PLC, and finally tighten the screws. To ensure reliable control system operation, the programmable controller is usually installed in a protective control cabinet to prevent dust, oil, and water splashes. To ensure the programmable controller's temperature remains within the specified ambient temperature range during operation, the installation machine should have sufficient ventilation space, with a minimum distance of 30mm between basic and expansion units. If the ambient temperature exceeds 55°C, a fan should be installed for forced ventilation.
To avoid electrical interference from other peripheral devices, the programmable controller should be kept as far away as possible from high-voltage power lines and high-voltage equipment. A distance of at least 200mm should be maintained between the programmable controller and high-voltage equipment and power lines.
When a programmable logic controller (PLC) is installed vertically, care must be taken to prevent wire ends, metal shavings, and other debris from falling into the PLC through the ventilation window, which could cause a short circuit on the printed circuit board, rendering it malfunction or even permanently damaged.
