Help choosing a PLC

Hello I am new to PLC's, and I need some advise on choosing a PLC that will work for me, The project I am working on will need 10 or so I/O ports for DAC or ADC inputs, it will also need an onboard realtime clock, have the ability to store data and send it onto the net via a dialup Internet connection. I would also like to be able to dial into the PLC and retrieve the data manually. Cost is definatly a factor, however this system will need to be a UL listed device..

Thanks in advance
Carl
P.S. this is my first post here and as my name implies I am new to PLC's, SO YOU REGULARS, be nice LOL

Well, first you're going to have to be more specific. 10 or so I/O, isn't a specification.

Questions you need to answer first:
Exactly how many discrete inputs?
Exactly how many discrete outputs?
Exactly how many analog inputs and type (1-5V, 4-20mA, RTD, etc...)
Exactly how many analog outputs?
Do you need the ability for online edits?

have the ability to store data and send it onto the net via a dialup Internet connection.

Click to expand...

How much data storage?

You can't choose a plc, until you know what you need.
I would suggest you start a spread sheet with a list of all your physical devices, what type of input or output they require, scaling, tag numbers, location, mfg. etc...
Also a P&ID of the process would very useful.

try this thread:http://www.plctalk.net/qanda/showthread.php?s=&threadid=11298&highlight=I/O+list


Ken

I look at it another way...what brand are you most likely to deal with in the future. Do you work for a company now that is using a certain brand?

As far as pricing and the basic features you mentioned then Automation Direct has those even in the DL05:
http://web2.automationdirect.com/adc/Shopping/Catalog/PLC_Hardware

Online edits can not be done on most "brick" (small I/O) type units but data collection/monitoring can be done...even via a modem. AD offers modems etc too.
http://web2.automationdirect.com/adc/Shopping/Catalog/Communication_Products

Any of the major brands can offer 10 or so I/O with analog if needed and use a modem.

Spicific answer to a vague question:

Suggested PLC with RTclock: http://www.automationdirect.com/adc/Shopping/Catalog/PLC_Hardware/DirectLogic_06/PLC_Units

Analog modulesscroll down the page some) http://www.automationdirect.com/adc/Shopping/Catalog/PLC_Hardware/DirectLogic_06/Option_Modules

Modem for dialing in or out: http://www.automationdirect.com/adc...Modems_-z-_Telemetry/Telephone_Modems/MDM-TEL

Choosing a PLC

Ok first off I would like to thank all of you for your replies

My project will involve the following

(1) Monitoring the voltage and current on 3 motors, 220vac single phase, aprox 6 amps each.

What I want to do is make sure the voltage is present at the relay that controls motors, each motor has a normally open 2 pole, single throw relay rated at 15 amps, it has a 120vac coil to close the relay.

I would like to monitor the voltage on both the line and load side of the relays, so that I could detect a failed relay. Also I could determine if the circuit breaker that feeds the relays is sending the voltage to the line side of the relay. (one thought here, if one pole on the realy failed, 110vac would pass through the motor and be present on the load side of the relay on the failed pole load side, so I would need to verify the true 220vac potential on the load side of the relay).

I would like to monitor the AC current on each of the motors.

I would also like to monitor the 120vac to the coil of this relay.

If everything is nominal with the motors and relays, and breakers, the I would just need the average current draw of the motors logged and sent once a day to a website via a dialup internet connection.

If a motor, relay,coil, or circuit breaker failed, then I would want that data to be sent immediately.

(2) I would like to monitor a RS232 Serial communications line between two devices that communicate at 4800 baud, I dont need to know what the data on this line is, I just need to verify that data is flowing on this line. In the case data was not flowing, In the case that data stops flowing, I would like to to know what device failed, I think this could be acomplished by seperating the data line and looking at each side of the data line to see which device is inactive and which device is trying to send/recieve data.

The status of this line should be sent once a day if nominal, if not then the data would need to be sent immediately, with the information on what device failed.

(3) I need a seperate RS232 serial interface to communicate with a device that will be sending and recieving ascii data. Probably no more than 100 kb per day. This data should be Logged and sent once a day form the PLC via the modem.

(4) I will need a port to connect with a PC to load my program instructions into the PLC.

(5) The PLC needs to have a realtime clock so data could have a timestamp.

(6) The PLC needs to have (or connect to) a dialup modem to send data.

Well I know this will probably NOT be enough detailed info to choose my exact needed PLC, but maybe it will be enough to keep this thread alive.

Thanks in advance

Carl...

Now that the advertising is out of the way, we can talk about your requirements.

The big challenge I see is the sending of data "to a website". Most web-based automation interfaces are maintained by server software on the web host that queries the control system, not by a controller itself.

I am not aware of any general-purpose PLC that can initiate a FTP client transaction. It's quite a challenge even to initiate a PPP Dialup connection to the Internet.

The rest of your functions can be done with general-purpose I/O and transducers. You can use voltage threshold switches to monitor your AC voltages, and current transducers to get 4-20 mA instrumentation signals into a PLC that correspond to the current flowing to your motors.

The RS-232 monitoring can be done by a serial watchdog; I like products from IndustroLogic for this kind of application.

I think you are either going to have to go with a PC-based control system or one of the exotic "open control" platforms to get the website interface that you want.

I think I could pull off an FTP session through the serial port of a ControlLogix, given enough time to program, but I think this is outside the realm of a "Micro PLC" of any sort unless you change the requirements to be exclusively polled from the webserver side.

This is a neat application; I'm looking forward to reading this thread.

Ok say I change my requirements and let the web server poll my PLC, what if I have say 50 sites set up with the exact equipment, would a web based server be able to poll this imformation in a timely manner, just say I wanted the sites polled every 15 minutes.

Thank you for your replies
Carl...

I didnt think that was advertising. I thought I was offering an inexpensive option(s) for a generic undefined project.

Many of my projects use phase loss and current sensing relays.
http://www.crmagnetics.com/newprod/relaySG.asp

I use aux contacts on starters, breakers and relays for verification.

I have used a modem in several situations to dial out on alarm. The same modem can be used to dial into the plc for monitoring etc.

I dont know a way to connect to ethernet via dialup, be easier to dial into a PC that is on the net OR connect the PLC to the internet.

I dont have a clue about the RS232 monitoring. I know its possible but not how to tell the plc a specific device isnt sending/recieving.

So far I have seen the need for maybe 2 ports...that depends.
I count 12 inputs but that could possibly be reduced to 9, no analog.
I am not sure about the serial watchdog, it may need RS232 or possibly could use 2 digital inputs (signal for which device).

So I get at top end
14 inputs
3 outputs
2 RS232 port
Real Time clock

Did I miss something?
Is there a BRAND that doesnt offer this?

OK

I would like to monitor the voltage on both the line and load side of the relays, so that I could detect a failed relay. Also I could determine if the circuit breaker that feeds the relays is sending the voltage to the line side of the relay. (one thought here, if one pole on the realy failed, 110vac would pass through the motor and be present on the load side of the relay on the failed pole load side, so I would need to verify the true 220vac potential on the load side of the relay).

Click to expand...

You wouldn`t have to monitor voltage to your motors only current. You could prove with logix if your motor was running with a didital input. Put a current monitor on either side of your relay. There are current monitors with built in set points also thier on timers. PLC logix = motor called for current <5 and >7. If this is true OK if not call out. Then just because the motor is running doesn`t mean its doing anything so you might need a flow switch, sail switch, or a sensor giving an input back to the plc. At this point you may not need to monitor current because if the motor is called and is doing its job through proof of logix everythings OK. As for logging the data you could have this polled through a pc and logged into something like (AB RSVIEW32) The tasks you have listed would be a pretty good under taking for someone that was very famialar with plc`s.
BUT ANYTHING THE MIND CAN CONCEIVE AND BELIEVE IT CAN ACHIEVE
Good Luck :!:

rsdoran said:

I dont know a way to connect to ethernet via dialup, be easier to dial into a PC that is on the net OR connect the PLC to the internet.

Click to expand...

I did not mention ethernet, I was just wanting to connect to the internet website and send up my data from the PLC.

Re: OK

Thomas Sullens said:

You wouldn`t have to monitor voltage to your motors only current. You could prove with logix if your motor was running with a didital input. BUT ANYTHING THE MIND CAN CONCEIVE AND BELIEVE IT CAN ACHIEVE
Good Luck :!:

Click to expand...

Thank you for you input Thomas,

The reasoning behind monitoring the voltage was to be able to tell what componet in the system failed.

Ken Roach said:

The rest of your functions can be done with general-purpose I/O and transducers. You can use voltage threshold switches to monitor your AC voltages, and current transducers to get 4-20 mA instrumentation signals into a PLC that correspond to the current flowing to your motors.


This is a neat application; I'm looking forward to reading this thread.

Click to expand...

Thank you for you input Ken,

Could you possibly post a link to the voltage threshold swithchs and the current transformers, I dont think I mentioned this but all the componets in this project need to be UL listed..
Thanks again for your reply

Carl...

Ken Roach said:

I think you are either going to have to go with a PC-based control system or one of the exotic "open control" platforms to get the website interface that you want.


This is a neat application; I'm looking forward to reading this thread.

Click to expand...

Did you mention PC, EEEEEEKKKKK lol

What you are trying to achieve is very do-able. I have monitored loads and contactors / transfer switches in the past in a similar fashion, remotely monitored and controlled, but the dial up modem is a little different.

I have used GE Fanuc 9030 for this type of application, and it is very popular in the standby power and energy management field. The GE's are extremely easy to program, depending on the software used. I have used all there current stuph, but prefer the old standby, LogicMaster90 whenever possible.

The bad relay pole can be overcome with an optical isolator (or relay) across the pole will indicate if there is voltage present across pole. If there is voltage present, then the relay has a bad pole. If there is no voltage present, then the relay is closed and operating properly, or not energized at all.

Overall, not hard to engineer, just hard to explain on "paper".

regards.....casey

Carl,

Go back to post 4 on this thread (from your's truly) and take a good look at all the links. I really think youll find what you need.