PLC + flow meters

My background is in conventional programming so this is all new to me, please bare with me.

I've been given the task of retrieving values from an flow meter and displaying it on the web. Can a flow meter be wired to a PLC for this purpose? From the tutorial it seems that a PLC can program on/off states but I was not clear on if it could retrieve values to a PC somehow. Am I way off base?

Your help is appreciated, thanks in advance.

KL

Well that depends on your PLC. Not every PLC would have
analog input but most do or can be upgraded with proper modules.

The PLC proposed is a GE Fanuc VersaMax PLC. From the specs it looks like it supports analog inputs. Specs

So once I know the PLC supports analog inputs a flow meter can be wired up?

Well it depends...
First you need to check what interface your flowmeter has.
typical outputs are analog 4-20mA but i've seen them
with others too (communication ports or pulse train etc.)

Thx for the prompt reply. I'll try to find more info and will post back.

If the interface to the flow meter was through a display unit that was RS232 compatible would that make things easier?

The VersaMax PLC supports analog input modules, so if your flowmeter can output either 4-20 mA or 0-10 VDC, you're OK. If your flowmeter can output a pulse train, the VersaMax has a counter module that can handle it. If you have to input a serial port signal, the VersaMax can do it, but it won't be as easy as either of the other alternatives. First, you need to know the details of how the flowmeter sends the data. If it uses Modbus protocol, and the flowmeter is a Modbus master, it won't be too bad. You can configure either of the serial ports on a VersaMax CPU (except for the Ethernet CPU E05) as Modbus slaves. If the flowmeter simply outputs ASCII codes at a periodic rate, you'll find the ladder logic to monitor the serial port and decode the incoming data to be cumbersome. If the flowmeter can only respond to external requests for data, then it gets even uglier. In that case, you have to put together the data requests in addition to having to decode the response.

Thank you Steve that was VERY helpful.

Do you have any comments on the Unitron Vision 120 PLC. I've spoken with an associate who has recommended this unit as something that is fairly easy to get up and running and has friendly developer software.

Would it also fit this particular application?

Thanks again.

Djshorty,

A few years ago I was asked the same question and I solved it in this manner.

In my case we were talking of 47 leveltransmitters and 40 micromotion massflowtransmitters. The leveltransmitters were connected on a Fieldbus foudation network and the micromotions were point to point connected. I used a Delta-V controller of Emerson with on one hand FF-netwerkcards and on the otherhand analog input which supported the Hart-protocol. If your system can support the Hartprotocol then you can not only visualize your flow but also a lot of other values such as totalizer, temperature ect.
Delta-V has a build-in Add-in towards Excel, so it was very easy to transport all of the necessary data into Excel.
This Excel file was available on the internal network and was picked up and published on the internet.
If you want some more info, just ask

Rudi

Another thing to think about is: if your flowmeter supports it, set it up to give a discrete pulse at a set interval ie. a pulse for every 100 gallons etc. Then just use an upcounter in the PLC and multiply the pulses and set up a time base to figure flow. Analog would be much better but pulses could work although accuracy wouldn't be as good.

Although my background is mostly in PLCs I solved this same problem without one. I used a Secure Network Interface(SNI Website) from Dawning Technologies. It's a little box (about the size of a mini hub) with a RS232 port and a Ethernet port that is programmed in BASIC to read and write to the RS232 port and create web pages. It continuously reads the flow meter through the serial port and saves hourly data to a text file. It has built-in FTP events to send these files to a PC or server. I even found a Java Applet to display flow data on a interactive chart displayed on a web page.

Sam

Samneggs,

I will be needing a PLC since my application also involves temperature monitoring but your solution sounds interesting. Do most flow meters support data aquisition through a serial port? And can you adjust this unit to take readings on shorter intervals than an hour?

Kev

Since accurate flow requires a digital time base and arithmatic functions usually a CPU is involved. Where there is a CPU some type of communication to it is often not too far away. So yes, most flowmeters I have looked at have a RS232 interface as an option at least.
I am using a mass flow meter that measures the temperature difference between two sensors while other types of flow meters can be temperature compensated. Reguardless, if it is the temperature of the media you are measuring that you need to know, it is usually available through the flow meters via RS232.
The intervals for recording can be anything through custom programming. I am reading the meter as fast as it spits out data, about once a second. The data consists of flow (SCFM), temperature and a cumulative total (CF). Through programming I update the web page every 3 minutes and log the data every 30 minutes. Those intervals could be any time from once a second to infinity. Then I log the total in a different file once per day. Useing the totalizer in the meter is much more accurate than working with instantaneous flow.

Sam