What are the specifications for COMPACT PLCs from Modicon? I have been using Allen Bradley and Siemens and they are rated at 60 Deg. Centigrade. Also I am confused on the user memory available. Typically for eg: a Allen Bradley PLC (SLC) will have 12K User+4K Data that is 16 K memory. But these compact PLCs have 512 KB? that's amazing memory for 256 I/Os! Can some one please help me?

 

Don't get caught up in the statistics game, they can easily be used to confuse and influence. For example, temperature specs. Is the high temp spec an ambient air temp or the internal temp of the PLC CPU? Is the low temp the guaranteed low temp at which the PLC will run or the temp at which it actually power up and run? Ask specific questions and get specific answers.

The Compact PLC model PC-E984-285 has a published operating temperature spec of -40 to +70 deg C.

Comparing memory specs between PLC manufacturers is another difficult task. Each uses memory different. Watch out for byte vs word specs.
The Compact PC-E984-285 is specified as having 32K words of user logic memory, 64K words of state RAM plus 128K words of configurable register storage.

Also, different programming languages use memory differently. IEC languages consume memory unlike ladder logic style languages. The use of unlocated variables reduces the requirements for state RAM.

The total memory size specification may include requirements for the PLC exec firmware (operating system).

And have fun with the scan time and logic solve time specifications...

 

<p>Modicon's Compact PLCs can sometimes confuse or surprise its users. Here is the skinny: Temperature range of -40 to 70 degrees C. The memory goes as follows:
<pre>
Programming MEM Data MEM
984-LL IEC
PC-E984-258 16k words 220kB 48k words
PC-E984-265 8k words 220kB 24k words
PC-E984-275 16k words 220kB 48k words
PC-E984-285 32k words 620kB 96k words
</pre>
<p>All models are available with conformal coating. The later two in the list accept PCMCIA cards (1MEG to 4MEG!), which can back-up your program or serve as PLC resident DAQ. They can do up to 1024 words of I/O (512 in, 512 out). They all have two RS-232 ModBus ports (EXTREMELY modem friendly) and a unique time-synchronization port ready for GPS systems (great for RTU DAQ). Finally, most of them can do InterBUS or ModBus Plus distributed I/O.

<p>Hope this helps.