PLC (Programmable Logic Controller) is a programmable control device, specially designed in the industry to control the process from simple to complex, depending on the operator that it can perform a process. series of programs or events that are triggered by triggers (also known as inputs) that affect the PLC or through timers (timers) or events counted through counters. . When an event is triggered it turns ON, OFF or transmits a sequence of pulses to external devices attached to the output of the PLC. So if you change the programs installed in a PLC, you can perform different functions in different control environments.
Control techniques have been evolving for a very long time. In the past, the control of the master loving system was performed by humans. More recently, control has been carried out in electrical applications, by switching relay contacts. The relays will allow switching of power without using a mechanical switch. We often use Relay to create simple logic interrupt control operations. The advent of computers has created a new step in control – PLC programmable control technology
PLC control in control system for overhead cranes is becoming more and more common. The application of PLC could simplify circuit and make the design easier, safer and more reliable. In traditional designs, relays and contactors are adopted. Starting of the crane and speed control of the crane is realized through AC winding and resistance series. This kind of design has low reliability, complex operation, high failure rate, power waste and low efficiency. Based on the above issues, this topic put PLC and converter on overhead crane control system and carried out thorough research, which indicates that after this improvement, energy consumption becomes smaller, mechanical wear-out is less and starting performance is better.
- I/O modules
Everyone generally assumes that when something goes wrong with a PLC, it is due to internal processor problems. Wrong!
A big percentage of problems are the result of I/O modules or field equipment. No need to panic either as it is not difficult to diagnose whether the problem is emanating from the I/O system or in the processor. Both types of problems have unique signatures allowing an even easier examination, and therefore conclusion.
- In or out?
If the problem is traced back to a specific I/O module, this means that it is usually an external one, like the aforementioned wiring errors. If it is an internal problem, this could actually result in erratic behaviour, large groups of failures, or even total failure of the programmable logic controller system!
However, one of the first checks to do now is the ‘integrity’ of the PLC. This doesn’t mean questioning whether it is a good, honest citizen with morals and a clean tax record, rather the integrity of the ground has to be electronically checked.
The power and ground wiring also needs to be examined further, to ascertain whether its loose, corroded or has damaged connections. The power supply should be checked; using a digital meter and both AC/DC voltages should be zero.
Another problem for the PLC can be the effects of electromagnetic interference (EMI) or radio frequency interference (RFI). These can be related to lightning strikes, welding in the area or handheld radio transmitters. The handheld radios used by maintenance staff, emit powerful radio frequency radiation, disrupting and interfering with any unprotected electronic equipment. Improvements in shielding, grounding and power conditioning can combat any EMI or RFI problems.
- Corrupted Memory
Frequency interference, power and grounding are all problems that can disrupt and corrupt the programmable logic controller’s memory, so it is crucial to verify the program is still correct and comparable with a backup copy on tape, disk or in the cloud. As with all data backups, ensure they are up to date and kept away from our old enemies, EMI and RFI, along with high temperatures and humidity.
When troubleshooting, a major aim is to find out why the internal status of the PLC (what it thinks is happening) is in conflict and not in agreement with the external situation (what is actually happening).
Our job is to determine the status of the relationship between physical I/O modules and I/O instructions in the PLC programming. Different manufacturers have different solutions and schemes, usually a terminal, handheld unit or PC (not PLC). Either can be used to check the internal status of the input / output in question.
PLC CRANE TROUBLE SHOOTING
- Troubleshooting ground loops
- Diagnostic PLC indicators
- Troubleshooting PLC inputs
- Troubleshooting PLC outputs
- Troubleshooting the CPU
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