Sensor monitoring using PC/PLC

roadrnnr

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Feb 2004
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I'm attempting to design a system that will monitor about 10 inputs at 4 stations(40 total) from a variety of motor and pressure sensors. I would like to display these values on a local PLC terminal, and record these values at a PC station. Any suggestions on a single PLC for the whole system(with all the inputs and plenty of display capability) or 4 PLC (one for each station). I have a ton of options and am not sure which one would minimize my hassles.

I don't need any other outputs from the PLC's except to record the data at the PC station, which I assume would be a serial or similar connection.

I've been looking at Mitsubishi Q-Series, but would like to avoid the hassle of buying 8 different unit and putting them together, and all without any local display capabilities. Any help would be greatly appreciated.

Cheers,
Matt
 
I'd use a separate micro-PLC at each location. My first choice would be the AutomationDirect.com DL-05 or DL-06, depending on how many I/O are discrete and how many are analog. They both have a Modbus slave port, which means virtually any SCADA or HMI (Human Machine Interface or Operator Interface) will talk to them without problems. They also have a second port for the HMI.

A second choice would be the MicroLogix 1000 or 1200, but it is a little pricier and uses Allen Bradley proprietary protocols. A 1200 model with 2 comm ports is due out soon, but right now only one comm port is available, if that matters. That means you will have to have your HMI on the same comm network as the PLCs.
 
roadrnnr,

I agree with Tom Jenkins that the DL-06 would be a good choice IF YOUR INPUTS ARE ON/OFF (DIGITAL) type. You said "pressure sensors", which implys to me that you need to read an analog level from at least some of the 40 inputs. If that is the case, then I recommend steping up a level and using the Automation Direct DL205 PLC, with five analog input modules. The DL-06 PLC only accepts two add-on modules. The F2-08AD-1 analog input module will give you 8 inputs per module. If you want local (or remote) display capability, buy an Operator Interface Panel such as the Automation Direct EZ-Touch or the EZ-Text.
 
Just to clarify, Lancie, the DL-05 can add up to 4 analog inputs, and the DL-06 can add four cards for a total of 16 analog inputs. If roadrnr needs more than that then I agree that the DL-205 is a great choice.
 
Just an addition to your AB MicroLogix suggestion Tom...
the current Series C firmware versions for the 1200 and 1500 support a fully functioned Modbus RTU Slave protocol.

Also the AB DF1 protocols (DF1 Full and Half Duplex) were never proprietary; the documentation describing them has been freely available for decades. It was simply that in the 70's Modbus got a head start on the market and became far more widely supported...
 
Tom,
Thanks for correcting my error. I see that you are indeed right, the DL-06 has four expansion slots instead of two.
 
Man, the guys on this forum don't miss anything. I forgot all about the Modbus on the MicroLogix!

Phillip, I guess technically you're right about DF1 protocol, and I even have a guide for it. It's just that very few other PLCs support it, so I tend to think of it as an Allen Bradley protocol.
 
Hey guys, thanks a lot for the info. I will actually need about 7-8 analog inputs (pressure, flow, 2x rpm, etc) as well as a couple digital inputs (overfill true/false, etc.) I'll be sure to take a look at the recommended models.

As an additional follow up, does anyone have recommendations about PC data logging software? I found a product from Azeotech that seemed as though it would fit the bill, but I have never purchased such software before and would like to build a reliable setup if at all possible.

Great site guys, and I'll be sure to try and help someone else out if I can.

Later all,
Matt
 

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