More help with PLC

ECM

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Join Date
Jan 2009
Location
IA
Posts
11
Not getting much help on my other thread, perhaps it is too much in depth for anyone to have much interest. So I thought I would break each part of my project down and try and solve my problems that way.

First off I know very little about PLC’s but I’m learning.

Here is the link to my original thread if you feel like reading through it. http://www.plctalk.net/qanda/showthread.php?t=44160

Here are a couple of questions for now.

I can purchase two SLC 500 from a local demo contractor, one a 7 slot the other a 10 slot both for $100.00. Both have all Ser A components and 115Vac power supplies. They both have an I/O adaptor modules 1747-ASB and several 1746-IA16 input modules and several 1746-OA16 output modules. Would one of the PLC’s be a good starting point for building a PLC for my needs or are they too old to mess with?

I'm mostly dealing with 4-20 mA and 0-10 Vdc inputs from sensors and three float switches that can be either 24 Vdc or 115 Vac. Basically to keep track of the level and gallon per minute fill rate of a tank. I know I would still need to purchase analog modules for that. As far as outputs it will be to turn on and off a couple of valves and relays that can be either 24 or 115 V also maybe some pilot lights showing status of each if I don’t have a HMI for this.

I'm not sure if the adaptor modules are of value in my situation or the Input and output modules are either for that matter. From what I read on AB website the I/O adaptor modules are for communication with other devices. Is this how you hook up to the PLC for programming? I’m planning on having a HMI, will these I/O adaptor modules work for hooking up a HMI also?

So to recap, basically my questions are:

1. Is either of the PLC’s a good starting point for the project?
2. Are any of the modules of value to me?
3. What are these I/O modules used for?


Any help is greatly appreciated.
 
the CPU for each of those would be in place of the IO module in the first (leftmost) slot. The single CPU would outweigh the cost of a complete NEW Automation Direct system. AB=$$$, they add another $ every year to that, lol.

I just got back on, saw this on the other thread, but I am out doing a real man's PLC job today...
 
I know just enough about AB SLC products to make me dangerous, nowhere near enough to be considered an expert, so take all of this with a grain of salt.

Since you didn't mention a CPU model, I wonder if you're simply looking at two I/O racks. The ASB module is used to connect a SLC CPU rack to additional racks of I/O modules. It's for those jobs where you need more I/O than can fit in a single rack.

The IA16 modules are 16-point discrete AC input modules. They are for connecting signals from things like limit switches, proximity switches, photocells, devices that tell you whether they are ON or OFF.

The OA16 modules are 16-point AC output modules. They are used to turn things like motor starters or solenoid valves ON or OFF.
Your 4 - 20 mA or 0 - 10v signals are not compatible with the modules you listed.

You will need RS Logix programming software running on a PC to create ladder logic on your PLC. The model of PLC you choose dictates the version of RS Logix required as well as the method of communicating between the PLC and the PC that runs RS Logix.

I would recommend against starting with the SLC. That product line dates back to the early 1990s. AB has not officially retired it yet, but it's not a horse you're going to be able to ride for very much longer. If you have an entire working SLC system, including programming software and cables, dropped into your lap, I'd say go for it. But, if you need to purchase much to supplement the stuff you get cheap, you'll be better off getting something more current.
 
I dont see why a slc 500 wouldnt work personaly, and for flow rate i belive you will need a flow meter and flowcomputer. you can trend it with trendx.
as far as your level controle for your tanks you could install high level and low level switches controling a dumpvaulve for high and a control vaulve to fill the tank back up when it gets low from dumping. no autiomation needed there.
and btw you can get alot of slc 500 cards off ebay prety cheap.

the I/O modulres are for handling inputs to your plc nad outputs for your relays or whatever.
 
SLC is a very good platform to start out with. However, it sounds like this is a one shot project so the price of the software is a big negative in this context.
 
Check out Automation Direct if you're just starting out. The hardware and software is high quality and reasonably priced. The software is even free if your program is 100 words or less, and you don't need to purchase ANOTHER program to handle the communications to the processor.

I work with Automation Direct and Allen-Bradley products. Both companies have good hardware, but Automation Direct doesn't rape your wallet.

Chris
 
the CPU for each of those would be in place of the IO module in the first (leftmost) slot. The single CPU would outweigh the cost of a complete NEW Automation Direct system. AB=$$$, they add another $ every year to that, lol.

I just got back on, saw this on the other thread, but I am out doing a real man's PLC job today...

Since you didn't mention a CPU model, I wonder if you're simply looking at two I/O racks. The ASB module is used to connect a SLC CPU rack to additional racks of I/O modules. It's for those jobs where you need more I/O than can fit in a single rack.


You will need RS Logix programming software running on a PC to create ladder logic on your PLC. The model of PLC you choose dictates the version of RS Logix required as well as the method of communicating between the PLC and the PC that runs RS Logix.


btw you can get alot of slc 500 cards off ebay prety cheap.

Thanks to all that have replied.

There is no CPU module.

I may have access to RS Logix, so having to purchase that will not be a problem. Learning exactly how to use it might be, but that is the fun part.

I do purchase a lot of my equipment on EBAY, so that should cut down the cost of the CPU and modules that would be needed.

Can anybody tell me which CPU and analog module I would need to run a SLC 500 that would be able to handle analog inputs for the 4-20mA and 0-20 Vdc inputs?

Keep in mind I would like to have a HMI so I'm not sure if that will make a differance, or if there is a special modual needed for hooking the HMI to the PLC.

I will take a look on Ebay, price them and weigh my options if I should be looking for a complete differant SLC, PLC or stick with what I have.

Thanks again.
 
Re pricing... it's not ALL just about hardware pricing... The hours spent coding must be considered as well.

I'm a fan of the Automation Direct stuff but 'cut my teeth' on the A-B and to be honest, if there's any Analog control involved at all stick with the A-B. AD are stuck in a time warp with their data manipulation (although rumour has it that big changes are on the way).

Having said that, personal preference these days is the Schneider product (Twido based hardware for the small jobs and Unity based hardware for the bigger stuff).

Muz
 
Re pricing... it's not ALL just about hardware pricing... The hours spent coding must be considered as well.

I'm a fan of the Automation Direct stuff but 'cut my teeth' on the A-B and to be honest, if there's any Analog control involved at all stick with the A-B. AD are stuck in a time warp with their data manipulation (although rumour has it that big changes are on the way).

Having said that, personal preference these days is the Schneider product (Twido based hardware for the small jobs and Unity based hardware for the bigger stuff).

Muz

Thanks I will take that into consideration.
 
you dont mention whether either one of these systems has a processor. If they are a rack with I/O cards and a remote I/O scanner module then they are just remote I/O racks with no processor and no control. You would need to buy a processor. I would recommend that you look at automation direct.com Depending on the number of I/O you need and the amount of analog, this may be a much cheaper approach and you can configure the system with new equipment for not much more than what used ab stuff costs on ebay or surplus. If you definetly want AB I would look on ebay first and check out slc systems that have a 5/04 processor or a 5/05.. the latter is ethernet ready and will perform the best with hmi and other comm needs. It will be more money though. ethernet devices are pricey even on ebay. I think I would stay away from the two systems you mentioned unless you know you are going to use 120 v and you can find a processor to do the job well. A 5/03 processor might do the job for you also but beware of the processor and communication ports on it if you dont have the necessary comm adapters and setup to talk to them. Some have rs232 some dont, some are dh+ which require special communications. Go for dh485 or ethernet. Stay away from the older units unless you have a pic module or a pcmk card and cable to talk to the units with.I hope this helps..
george
 
Check out Automation Direct if you're just starting out. The hardware and software is high quality and reasonably priced. The software is even free if your program is 100 words or less, and you don't need to purchase ANOTHER program to handle the communications to the processor.
Chris

why would you pay for RSLinx? It comes with RSLogix500 or can be downloaded from AB website...
 

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