PLC code for Analog Signal to Totalizer...

fabian24

Member
Join Date
Jul 2007
Location
Sharjah
Posts
16
Well, I have been searching and trying for days and not come to an accurate solution on this simple but complicated peice of programming...

I have a flow meter which gives an analog signal input of 4-20 mA to the PLC. It's a AB Micrologic 1200. This signal is scaled to 0-1600 l/sec.
The signal displayed is perfect and accurate.

The next step is to totalize this flow.
Could someone please give me some programming code on this.

The flow transmitter also has a pulse output and this can also be routed to the PLC if required.

Please Please someone help on this one.
 
Ideally, you would communicate digitally but the pulse is the next best thing. If you want your PLC digital value to match an intelligent totalizer, establish comms between the PLC and the totalizer.

The pulse will replicate very well too, and either method will have some lag, although the pulse should be more repeatable, and there is probably lag in the built-in display.

The disadvantage to using the pulse is that your PLC can accumulate missed pulses and develop an offset, whereas with a message on a communication channel can make up for missed messages and likely give you the power to interact in greater detail, perhaps perform calibration and read status from the totalizer.

I would go for the pulse only if I knew the signal would be easier to interface and I could prevent or properly code for missed pulses, and a communication option is unavailable, or too expensive to implement (be that in man hours of set up or actual hardware).

Can you tell us the manufacturer name and part number or model number of the flowmeter/totalizer?
 
Yes, we have some Promags not sure which model. Ours have built in analog and pulse I believe. I say there's a good chance that one may support built in RS-232 and RS-485, but check your manual. If you want it quick and cheap, then use a pulse on the existing analog wire,

If you want to spend some time figuring out how to communicate with it, RTFM and see if you can do it without any additional hardware.

My internet is too slow for their site, and I don't want to register again from home, but they will definitely have a manual for you. You will likely need the whole model number including option codes.
 
Dear sir, could you please assist me in writing the code. I am sure that the flow meter has a pulse output.
I am new to this. Would appreciate your help.
 
Sure, post the code, and a copy of the electrical schematic and I will look at it tomorrow or the next day.

Zip the files and attach them to a post.
 
Last edited:

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