kWh meter

[desuhardi 0]

Hello all, I want to make kWh record with PC. kWh meter is Merlin Gerin, with 1 impulse of 200ms every 10kWh. Is it possible to connect this pulse to digital input of PLC, like as Mitsubishi FX, Toshiba T1 or others ? Or any other idea how to get kWh data to PC ? Thank you

[Crossbow 295]

As long as the pulse can provide 24VDC, sure you can connect it to the PLC. And then in the PLC use that signal to count.

[desuhardi 0]

Hello Crossbow, Thanks for your reply. Is it enough for digital input of FX to receive 200ms signal or need pulse input ? How about maximum length between kWh meter and PLC ? Output from kWh is dry contact. Thank you

[panic mode 246]

even standard PLC input will see pulses of 5-10ms or longer. this means that 200ms is slow enough for regular PLC input to see it. this doesn't mean that your PLC program can catch it if your scan time is too slow or if the time between pulses is too short (but i hope it's not because with 10kWh pulse every 200ms and next to no gap between pulses would mean load in order of some 100MW). usually PLC scan time is in the 5-20ms range, but of course it can get significantly longer. one can of course use interrupt driven routine to count pulses so even in case of very long scan time, this would be no problem. so what kind of distance/cable length we are talking about?

[funfrok 0]

I think it can be better if a meter, which stores energy usage internally and provides it through serial access, is used.It would be harder and more expensive i guess. But it would be more accurate, and not dependent on the PLC. If PLC stops you will lose data when you read usage with pulses.

[Goody 5]

and the thought struck me, if this is all the plc is used for why not use just a digital counter. :)