Determining Number of I/O

Hello,

I am using an AB CompactLogix L33ER in the design for the control of a pump station for water irrigation that will have 2 pumps, VFDs, an HMI, a pressure transmitter, a flow meter, and a thermistor. I need to purchase the I/O cards which means I need to determine the number of analog and digital I/O in order to select the appropriate cards. Is there a method how to do this before the PLC program is written? Thank you very much in advance.

Get some details and count them up !

Do the VFDs connect to EtherNet/IP ? If so, they will need no I/O to connect them to the controller.

Do the pumps have sensor or actuators other than the VFD ?

What kind of signal does the pressure instrument use ? My guess is that it's an analog 4-20 mA loop.

What kind of signal does the flowmeter use ? Is it a pulse train or an analog signal or something else ? The flowmeter might require a specialty module. Does the flow need to be monitored for custody control or financial metering ?

What are the characteristics of the thermistor ? Is it a conventional RTD like a 100 ohm platinum unit, or is it a 'go/no go' discrete overtemperature switch ?

It might make more sense to use signal conditioners on one or more of your signals so reduce the number of specialty modules needed by the controller.

If this were my system I would be looking at the less expensive 1769-L16ER and L18ER controllers rather than the L33ER, just because the I/O count is so small.

Based on your post you already have your i/o count just tabulate it and add some spares for example i have 10 DI i will purchase a DI card which is capable of 13 DI so it can be a Card with 16 DI because their is no card that have exactly 13 DI

Hello, I have discovered more details since I posed my question but here are answers to your questions to make sure I am counting correctly:

Do the VFDs connect to EtherNet/IP ? If so, they will need no I/O to connect them to the controller.
The VFDs are hardwired to the PLC.

Do the pumps have sensor or actuators other than the VFD ?
No

What kind of signal does the pressure instrument use ? My guess is that it's an analog 4-20 mA loop. Yes

What kind of signal does the flowmeter use ? Is it a pulse train or an analog signal or something else ? The flowmeter might require a specialty module. Does the flow need to be monitored for custody control or financial metering ?
It is an analog signal and it is not being metered.

What are the characteristics of the thermistor ? Is it a conventional RTD like a 100 ohm platinum unit, or is it a 'go/no go' discrete overtemperature switch ?
I found out the thermistor is not included now

If this were my system I would be looking at the less expensive 1769-L16ER and L18ER controllers rather than the L33ER, just because the I/O count is so small. Good idea.

What about alarms though. Should this be included in the IO count?
There are so many different kinds of IO cards, how do I choose these?

Thank you for your advice.

Depending on which controller you use, I recommend reading the Selection Guide for the related I/O platform. For the L16ER and L18ER controllers, this is 1734-series POINT I/O, and for the larger CompactLogix controllers it's 1769-series Compact I/O.

Alarms are virtually always internal memory registers and are not included in the I/O count. You might be coming from experience with legacy DCS systems where a "point" could be a physical device or a logical device, while in a PLC a "point" is considered a single physical input channel.

Selection Guides and User Manuals are all available from the literature.rockwellautomation.com server. Use Google or the built-in search function to find documents like 1734-SG001.

One of the first steps of any automation project is counting up your I/O, so commence to doing so.

A typical hardwired VFD is going to need Start and Stop outputs, Running and Fault inputs, and an analog output channel for reference.

A starting point for module selection would be to look at modules like the 1734-IE2C. It's a 2-channel analog Current-Loop (4-20 mA) input module for the POINT I/O platform. One of those could serve both your flowmeter and your pressure instrument.

I would check out the 1769-L2x processors as well. The 1769-L24ER-QBFC1B has 16 digital in, 16 digital out, 4 analog in and 2 analog out, power supply and ethernet all on board. By the sound of it, that would probably cover everything in your project without any expansion cards.

Your other option would be the 1769-L16 series. They don't have the analog inputs or outputs, but the expansion cards they use are the 1734 point I/O cards which are significantly cheaper than the 1769 compact I/O cards. So it might work out cheaper. Just keep an eye on the limitations of each system if expansion is planned in the future - each PLC has a different limit on the number of cards your can attach to it, and the number of ethernet connections (among other things)

Edit: just noticed you say you're using an L33 processor. That's quite an expensive way of going about it IMO but if that's what you've got to use, I'd be going for:
Processor
Power supply
1769-IB32
1769-OB32
1769-IF4
1769-OF4

That will give you 32 digital in, 32 digital out, 4 analog in, 4 analog out. Should be plenty.

Thank you very much for everyone's advice so far! One more question. How do I determine how big my HMI and the corresponding logic module should be? I assume what I need to display is what size but how is this determined?

dskplc said:

Thank you very much for everyone's advice so far! One more question. How do I determine how big my HMI and the corresponding logic module should be? I assume what I need to display is what size but how is this determined?

Click to expand...

what do you want to display?

From the project description the HMI screens will display · *Pump station overview
· *Operator login
· *Pump station local/manual controls
· *Alarm/Fault annunciation


Does the choice depend on the logic module?
Thanks again.