reading flow total

Ok guy's and gal's. Here is my question. I have a micromotion flow meter reading the flow rate (ma 4-20 at 0-200 lbs/min and 0-30840.and in my program I am adding a batch amout to a vessel. I have converted this and am close but not close as my boss wants. How could we get this exact?

swaneyj; said:

I have converted this and am close but not close as my boss wants. How could we get this exact?

Click to expand...

You can't with analog signals.

Can you switch your meter to a pulse output and count pulses with a digital PLC input? This is the only method I know of that can be exact.

What type of meter and PLC are you using? We have a similar situation where we are stuck with analog but took steps to maximize the accuracy. It's closer than before, but never exact.

Another method might be to let the flowmeter control the batching if yours supports those types of features. That can be PITA too, if you ever need to change parameters in the meter to change batch sizes, that can make operation more complex or require extra engineering to KISS for the operators by communicating from their normal controls (HMI through PLC?) to the meter.

What have you converted and how exact do you want it? It also may help if you can post your program. Zip it first.

There are ways of doing it with the analog signal.
One of the ways is to establish a flow by reciculating the
loop and then opening a 3 way valve. This would require a variable speed pump or a fixed pump and a analog operated valve along with a pid loop.
Years ago we did another method called it a timed batch.
Recirculate, establish flow and then open a valve for x amount of seconds depending on the batch size. We where using a SLC504 with a pid loop and a timer where we calculated the amount based on a recipe. It was extrememly accurate (+- 1 %).
What are your flow rates and tank sizes? Is it always the same batch size?

What control do you have over the flow?
you can take timed 'snapshots' totalize them and know how much you are recieving but if there is no way of limiting the flow then you will bu unable to control the final batch ammount

If you can't do it digitally, you can't guarantee your totalizer will exactly match the display on the meter.

Ours is now within 1% over a 24 hour period with flow rates from zero to 500gpm with the addition of interrupt routines to take fine resolution snapshots of perfectly scaled and calculated ADC data, and we even threw in the measured variation of the execution of the routine to get there, but still, 475,673.1 <> 473,867.6 to the Engineering Manager.

Go digital, or write the code design spec. including the actual variation. People think that perfectly calculated and calibrated high resolution is enough to totalize GPM into G, but they don't seem to realize that the M is critical to accuracy, so how do you communicate the Time in the original GPM signal so that it can be correctly divided on the other end?

You can't.

Go Hart.

Go serial.

Move the wires to DC I/O and reprogram to count and totalize pulses. (that's a right now kinda "make it exact" answer usually at only the cost of your time).

OkiePC, do you have a example of how to program the pulse count? We do have a slc504 they are doing this with a prosoft card. But this is going to a plc5/40e. I could possible go to a remote I/o frequency card. Not sure how to go about it?

Remote i/o and high speed don't play well together. You may not need high speed depending on the rate and resolution of the signals and your application.

Most totalizers will allow you to specify a pulse rate so that you can make a pule mean whatever units you want and set it up to be slow enough that you can read into a regular even remote digital input without speed issues.

If you totalizer digital output turns on for a half second every ten gallons, then your total can be exact within ten gallons. If your process allows you to read a pulse every 0.1 gallons, then your totalizers will match to within 0.1 gallons.

So, figure out the required resolution and expected rates first, then pick interface and hardware.

Ok Not having much luck with this!!! I have the micromotion flow set up and have tried writing code to do this with a IP4 card in the remote i/0. Got the BTR and BTW set. With the help of the techconnect guys. I have used some of their sample codes. It's just not doing like I need it to. I will try to send someone the code if they can take a look and give me any advice Please!

swaneyj said:

Ok Not having much luck with this!!! I have the micromotion flow set up and have tried writing code to do this with a IP4 card in the remote i/0. Got the BTR and BTW set. With the help of the techconnect guys. I have used some of their sample codes. It's just not doing like I need it to. I will try to send someone the code if they can take a look and give me any advice Please!

Click to expand...

Please ZIP or your Program and Post it on this thread -
Also which PLC are you using?

Here it is

I hope I did this correct. My plc is a 5/40

the file looks ok - i am unable to open it tonight - will look later