These are electronic devices that plug into the CPU, designed to store information temporarily or permanently. There are two types of memory: volatile (RAM) and non-volatile (EPROM and EEPROM), depending on whether or not they require electrical power to retain information.
The memory capacity of these modules is designed for different sizes, the most typical being: 2, 4, 8, 16, 32, 64, 128, 256 Kb, and more, exceptionally.
The different types are detailed below:
Ram Memory (Random Access Memory)
This type of memory is used to store the user's program during its development and testing, where it can be constantly modified. The contents of RAM are volatile, meaning their contents are lost if the power supply is disconnected.
Therefore, to prevent data loss in the event of a power outage, it is necessary to safeguard the data with a long-life battery that plugs into the CPU. These batteries are available for all types of controllers and have a lifespan of 2 to 5 years, depending on the CPU type. It is therefore important that this battery be kept in perfect condition throughout the PLC's operating life.
Eprom Memory (Enable Programmable Read Only Memory)
It is a plug-in, non-volatile memory module, meaning that the information it contains is retained even when power is lost. It is typically used to store final, tested, and properly debugged programs, and can be transported and used in any controller of its brand and type.
To program this module, you need to use programming devices specifically designed for this purpose, while to erase it, it must be exposed to ultraviolet light for 15 to 45 minutes. Therefore, one unit is required for writing and another for erasing.
EEprom Memory (Electrically Erasable Programmable Read Only Memory)
This module has the same characteristics as the EPROM module, with the only difference being that erasing is done electrically; that is why it is called electrically programmable, read-only memory.
For these types of modules, the programming devices perform both functions, programming and erasing.
PROGRAMMING UNIT
Programming devices, also called programming terminals, are the means of communication between humans and machines through writing and reading. With these terminals, we can modify, monitor, force, diagnose, and fine-tune programs. These devices consist of a keyboard and a display unit. The keyboard displays all the symbols (numbers, letters, instructions, etc.) necessary for writing the program and other actions mentioned previously. The display unit shows all the programmed instructions or those stored in memory.
Programming devices are an important and necessary tool for communicating with the PLC, but physically independent, which allow us to:
• To write programs through a list of instructions or through a graphical method, as well as to modify or delete them totally or partially.
• Read or delete programs contained in the CPU's RAM memory, or also in EPROM or EEPROM memories.
• Simulate the execution of program instructions by forcing inputs or outputs.
• Detect and visualize program failures or failures originating in input or output field devices.
• Visualize/Perform the transfer of programs contained in RAM or EPROM memory to different peripherals, such as: magnetic disks or printer.
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Hello José. .
I have a machine that is over 15 years old. It consists of a computer containing a SCADA program (where data is displayed and entered into the PLC). The PLC, in turn, connects to input and output interfaces located in the control panel.
It turns out that one of the PLC boards, where the CPU is located, has a power supply with different voltage levels. This supply failed, and an electronics technician came and removed the board to replace the power supply. He also replaced all the capacitors on the board. The power supply now works, but the PLC doesn't seem to be managing anything. That is, it receives all the signals it needs to initiate its work sequence, but it doesn't respond with any output. The strange thing is that it intermittently keeps one output activated, but that's all it does. .
All machine operations that are direct, i.e., those that do not go through the PLC, function. .
Could the program be corrupted?
Could part of the program have been deleted?
The strange thing is that there is an output that is activated intermittently, and this did not happen when the machine was working properly.
Hi Jose,
It's difficult to help you without precise details about the PLC or equipment. Given its age, it seems the best course of action would be to replace the PLC and, if necessary, reprogram it.,
If possible, force each of the PLC's outputs and inputs to see if it does what is expected; this way we can rule things out.
Hello, teacher… my name is Andres Herrera, I am studying automation and control and I have a question… the professor occupies this space in the memory of the PLC (TIA Portal CPU 1200)
Digital inputs MB0 to MB1: Which digital inputs correspond to this used memory space?
Digital outputs MB6 to MB7: What digital outputs correspond to this used memory space?
Greetings, Mr. Jose Carlos Villajulca.