PLC Logic to get energy consumption of a Pump

Hi there,

I have a requirement to display the energy consumption of a given pump following each cycle of a machine.

There is no Energy meter, CTs or intelligent overloads etc installed but our "genius" at site says if I know the hydraulic oil pressure & flow I can multiply by a factor and this will give me the power consumption.

Is this possible or is this nonsense?

This may help, under pump formulas:

http://web.applied.com/assets/attachments/779D4407-D2AE-6FAA-7DA1CEDE2268977B.pdf

I like the one formula in there.

fluid HP= (pressure in PSI* flow in GPM)/1714

Then convert to.watts. 1HP=746 watts
now you know the work being done and should be able to calculate energy Comsumption. from there. I don't think it will be deadly accurate but it will be close

With new soft starters or electronic overload relays it's posible to read Kwh.

Wouldn't these formulas just give you the power absorbed by the pump? This is not the same as power absorbed by the motor, right?

A "cheap" solution would be to put a (or 3) current measurement on the phases. Assuming your voltage is pretty stable, and you know the cosp of the pump, you could calculate a number.

Better is to put a kWh meter or smart relay or something.

We use this:

Schneider iEM3135_63A direktemåler m M-bus 63A 3P +N A9MEM3135
Search here http://efobasen.efo.no/, el nummer 80 631 10

Cost is about 1200 NOK.

Rather than using a formula, I guess one could put on a clamp-on meter to measure the current then plot it against the Delta-P. That would give you a real world correlation of power vs head than you can fit it into a polynomial equation and use it in PLC.

DwSoFt said:

I like the one formula in there.

fluid HP= (pressure in PSI* flow in GPM)/1714

Then convert to.watts. 1HP=746 watts
now you know the work being done and should be able to calculate energy consumption. I don't think it will be deadly accurate but it will be close

Click to expand...

If you take the "water hp" from DwSoFt's formula and divide by the pump efficiency and motor efficiency and multiply by 0.746 you will get the motor electrical power draw.

Attached is a a spreadsheet I use for this. Fill in the blue values and the red values are the results.

Hi all,

Some great suggestions there so thank you guys. I don't think it has to be real accurate. Just a decent approximation. The machine cycle takes approximately 12 mins. Following this I need to give a total of Energy used.

fluid HP= (pressure in PSI* flow in GPM)/1714 was a calculation I could use. Could I use this is if my pressure transmitter is Bar and my flow is l/s?

Then this is only instantanous HP right? I guess I will have to sample this over the duration of cycle?

I should mention also that depending on the step the machine is in during the cycle the pump work will vary very differently. Sometimes the pump has a pressure setpoint of 15 Bar to achieve, others it has 200Bar.

I can see no reason you couldn't use the same formula, as long as you do the conversion right.

If your pressure SP varies dramatically you will have to make sure you take regular samples - i.e. instead of adding up the total flow and working out average pressure at the end over the whole cycle, take samples roughly every second (more or less depending on just how quickly it varies) and average the last few samples. Then you'll need some totaliser logic.

I'd be interested to see how accurate it ends up! Perhaps once you get it working you could throw a clamp meter or kWh meter in there and manually do a calculation off a cycle, see how similar the results are? Or at least, that's what I'd do, if only to satisfy my insatiable desire to poke at things I don't know