CPU Selection (PLC or DCS)

The product literature should tell how many analog/digital inputs/outputs can be supported. You didn't say who manufactures the 6ES7315-2EH14-0AB0, so most potential responders may not know the answer. You might get lucky, though.

Anyone into controls knows any part number that is constructed as #XX####-#XX##-0XX0 is Siemens. All you need to do is Google that number and you get the data sheet.

Reported, with prejudice.

When you ask two questions, one strategic (PLC or DCS); the other tactical, (which model for a given I/O count), it indicates a total separation from your involvement with a vendor up to this point. That is a serious mistake for any project beyond the trade school PLC stop light or parking garage project, given your experience level. The commonly expressed wisdom by people who make these kinds of decisions in answer to questions like yours is that vendor support over the long term should be a PRIMARY consideration. You can take whatever advice appears on this or any other forum, but a wiser approach would be to contact local vendors and engage their help in evaluating this project, because that gives you some means of evaluating the vendor as to how they'll treat you once you're a customer. If you're asking on this forum because the vendor whose product you cited has blown you off, you need to look for another vendor. In the USA, all vendors approach the market in a similar fashion. The PLCs are sold and supported by one distribution channel, the DCS is sold and supported by a different channel. If that's the case in your locale, you should be talking to at least two vendors, the PLC vendor and the DCS vendor for whatever brand you're considering. I apologize for gigantic paragraph format, it is an artifact of the iPhone over which I have control.

Hi Carl,

Nice answer (and GA). Some very good points. Depending on the nature of the system, selection can be arduous at least.

I was going to say USE PARAGRAPHS! But I understand "it is an artifact of the iPhone over which I have NO control."

Read the specs of the cpu, compared to your design system. This is objective, if you want a faster response system both I & O probably you need a faster processor CPU.

All CPU got specs, I am sure you have understanding with the parameters of it or consult your manager or one level above you. If in doubt. Do not decide not unless all is clear and they also agree. Otherwise, you are screwed certainly if it is incapable to handle the system-whatever it is.

It does mean you are not fit for the position since, you are amateur on the selection - this means you need from every now and then approval from superior. Incapacitated.

Ask manufacturer or system integrator best advice.

The wise thing to do is ask a quote on supplier's best offer. You'll get their best recommended CPU -simple. Just give the process parameters, variables and requirements. Read and watch youtube --plenty of tutorials available

Also,if the system is not all new, say a modernization, evaluate the existing sensors or instruments (baud rate) capability - means how fast the instrument can be updated by your CPU. Consult client if to what extent of accuracy he is desiring compares with the existing instruments. If he wants totally fast and accurate, decide to replace might as well the sensors or instruments.

Take this analogy (buying fast CPU, slow sensors) is like a brilliant kid but with obese physique. How he may able to find solutions to win a marathon perhaps - he could not just possibly do it. He is limited with the hardware

(buying a slow CPU, fast sensors) it's like a ALS diagnosed athlete. The body is capable but the brain is delayed and limited neuro-function.

II'd say talk to the equipment vendors. Between them, you will certainly form a view, and then you can decide for yourself.

AP1

Your suggested Siemens S7/300 CPU is quite capable of handling the "relatively small" I/O count you mention. World-wide, Siemens has the largest market share; in the USA it is second to Allen-Bradley (Rockwell). Its bus communication is one of the standard ones most HMI manufacturers will support, so that should be no problem. If you are in the USA, finding qualified Siemens programmers is not nearly as easy as finding programmers for AB and others, because of how it structures programs (blocks, not files). The I/O count you mention suggests the probability of your using distributed I/O, which this processor will handle easily. Doing that will significantly reduce the cost of running all those I/O back to a single point.

Good luck with your project.

--JMM

A choice between PLC and DCS is more related to what process you are attempting to control, the type of parameters you are inputting, and how much feedback information you want to display rather than the I/O count. Control more complex than PID loops, really high speed counting or 16bit servo control, go for DCS. You can do all these things with PLCs but the programming is complex and the results are usually a compromise (my programmers use the word "clunky")

I have been delivering control systems for 40 years and have yet to come across a project of this size that did not expand it's I/O requirement during the construction phase. If the numbers you have quoted don't include at least a 25% safety margin then allow for the extra capacity then specifying your CPU. Not using all the capacity you have available is easy and carries a low premium cost. Having to upgrade your CPU at some future date is a pain in the ****

I do not know the application but your digital input count seems low. The PLC/DCS is probably going to be the most reliable part of your system. Stuck valves, air line failures, slippage, loose linkages, poor lubrication, tripped motors, wear and blockages all take a toll on system reliability. You have 200 digital outputs but appear not have enough inputs to confirm that the operations generated by those outputs have happened correctly.

That input count would be so if there was a need for control feed back or a positive revertive indication, or confirmation of every op.

eg one op might be an alarm annunciator, you don't need the PLC to be told that a siren is blaring.

The feedback could also be an analogue ip.

That is the S7300 series - good start. Now you need the manual for the S7300 series to get the details you need to choose the associated I/O cards. Siemens likes to put the real pertinent data in the process manual, not the cards manuals. You know - a Siemens distributor can do this for you.

Allow me to correct this - that is an S7 (space) 300, not a S7300. Sorry.

Were one to select the <...6ES7315-2EH14-0AB0...> without knowing whether it can deal with <...AI=24, AO=12, DI=100 and DO=200...>, then the selection would be invalid, and would indicate an either an abstruse methodology or an incompetence that could be rectified by suitable training.

<...anybody please help...> Equipment vendors are the <...body...> _{[pluralise, please]} that can do this, and the simplest way of reaching them is by telephone in the first instance. Should that have not taken place so far, then it would suggest laziness in addition to the one of the features above.

Selection should also consider the standards and stockholding of the end user's spare parts, and Maintenance Technician training. To ignore these details would be crass, which could also be added to the above features.