Transfer pulse over a long distance

[s10jam]

Hello. I have very little experience with PLCs so please bear with me.

Problem: We have a pipe with two meter systems that are 10 miles apart. These meter systems output a square wave pulse that shows how much liquid is flowing through them. If they are equal, everything is fine. If there is significantly more through Meter System A than Meter System B, we know there is a leak. Obviously, we cant just take a 10 mile long wire from Meter System B back to Meter System A to compare them.

Question: With network enabled PLCs, can we configure a PLC at Meter System B to read these pulses and then, over our existing network, recreate these pulses through another PLC at Meter System A for comparison?

 

[mk42]

Hello. I have very little experience with PLCs so please bear with me.

Problem: We have a pipe with two meter systems that are 10 miles apart. These meter systems output a square wave pulse that shows how much liquid is flowing through them. If they are equal, everything is fine. If there is significantly more through Meter System A than Meter System B, we know there is a leak. Obviously, we cant just take a 10 mile long wire from Meter System B back to Meter System A to compare them.

Question: With network enabled PLCs, can we configure a PLC at Meter System B to read these pulses and then, over our existing network, recreate these pulses through another PLC at Meter System A for comparison?

You could put a PLC at each location, and have them communicate, yes. However, it probably doesn't make sense to try to have the PLC's communicating pulses. I would think it would make more sense to have each PLC monitor its own flow meter, and turn it into an integer/real, and then the PLC's can compare those. I'm not familiar with the process, so I don't know what math would most usefully transform the pulses into data. You could want a first order filter, or an avg of the last 15 minutes, or a running total, maybe.

 

[s10jam]

We have equipment that does the actual comparison at the first station. My main issue is getting the pulses from Meter Station B to Meter Station A.

I may have oversimplified the situation in my original post.

 

[OkiePC]

I agree with mk42 in that it makes more sense to have the PLC do the counting and share a real value, unless the pulses are relatively slow, then you may be able to replicate the pulses and keep things simple from the perspective of your existing arrangement. Still, I think you will want to also share a total or engineering unit of value in order to confirm that you have not missed any pulses due to comms losses which can sometimes be beyond your control.

 

[s10jam]

I don't disagree with either of you, but the current equipment is limited to pulse input. It cannot use real values.

 

[s10jam]

Side question: If we were to only use PLCs as you are suggesting, are there models that would let use use a formula to compare? For example, only trigger an alarm if the flow rates differ by 2%.

 

[howardepgco]

I am willing to bet that all PLC's will allow you to do that.

 

[s10jam]

Ok. The more I'm thinking about it, the more these suggestions are making sense. I suppose that I need to brush up on the capabilities of PLCs to truly understand the best configuration.

 

[howardepgco]

You also need to know your scaling factors. How many pulses per unit of measure.What kind of measuring device are you using?

 

[s10jam]

Our measuring equipment that is currently connected to each meter adjusts for K factor and temperature to give a a gross corrected volume. This is another reason I will like to leave the current equipment in place.

 

[howardepgco]

Do you use a Mag meter or paddle wheel? Regardless of what you use most measurement devices will give you either a 4-20mA or pulse per unit output or both. You can use these outputs for most PLC's and scale them in your PLC to match the measurement device.

 

[s10jam]

I'm not sure if the PLC is capable of calculating the Gross Standard Volume. Our equipment is specifically designed to do that.

 

[howardepgco]

I think they can. You provide the math and they will make the calculation.

 

[howardepgco]

What is your measuring device?

 

[s10jam]

FMC MicroFlows. For this customers application, an approved device must be used such as this one. I think our new plan is to use MicroFlows to take in the meter pulse at each location and feed the PLCs GST(not GSV as I stated previously). From there, the PLCs can compare the GSTs and make a decision on whether or not the totals have varied past the preset value.