S7-200/300/400

Hi I wanted 2 know the basic differemce btw siemens s7-200/300/400 & I want 2 automate a 25tph lpg boiler...which is goin 2 be the best choice & why??

Also are there any other alternatives besides PLCs being used in industries 2day for automation??

It will be extremely difficult to recommend a PLC for a 25tph lpg boiler based on the information you've given us (none...)

What exactly are you controlling?
How many i/o points? analog?
Needing to network to anything? If so, how?

All of those questions, and questions like them, will need to be answered in order to recommend a solution.

You should be able to go to Siemens' website to see the differences between their various S7 platforms.

There is not one single basic difference between these PLCs. To name a few:

1. Cost.
   S7-200 is a low-range PLC, S7-300 is middle-range and S7-400 is upper-range, therefor the cost is increasing with the series number.
2. I/O count.
   The same goes as for cost.
3. Programming software.
   The S7-200 is in fact a Texas Instruments PLC and not a 'real' Siemens PLC. The software to use is Step 7 MicroWin.
   Both S7-300 and -400 are 'genuine' Siemens PLCs (the successors to the S5 ranges) and are programmed by means of STEP 7, which exists in three different flavours: Lite, Standard and Professional. Of course the price goes up from the first (which is free) to the last one in the row (about US$ 2500, I believe).
4. Networking capabilities.
   As an example: S7-200 can only act as a slave on Profibus, whereas S7-300/400 can be masters.

I'm sure some of my fellow forum buddies can add to this list.

Kind regards,

Actually I need 2 control the level, pressure & temp of boiler & level & pressure of deareator (water purifier 4 boiler)

There are
analog inputs: 9
analog outputs: 5
digital inputs:3
digital outputs (alarms): 11