Hello,
I have a Omnimeter II v.3 connected to 120 Vac single phase 60 Hz, max. current reading 10 amps. single ct (200 amp)
Logged data sampled every minute, a few examples:
Vac I(amps) watts pf calculated watts (V*A)
116 7.8 922 1 904.8
118 7.8 934 1 920.4
all recorded data has this error
When you calculate the watts from the voltage ,current and power factor there is greater than 1% error,
not sure how you calculate this result, were is the error introduced.
Thanks
Greg
watt readings accuracy
Re: watt readings accuracy
Hello Greg,
Thank you for your questions.
As far as I understand, the meter samples volts, amps, and power factor at 25,000 times per second. It then takes these values to calculate kWh and at various moments of say a second (the values the meter passes to the RS-485 bus or to the LCD screen do not necessarily overlap from the same moment in time). You are correct that the formula is volts * amps * power factor.
Another thing that can happen is that the values are not rounded like you would assume. So if the meter is measuring 7.8789 amps, it will report it as 7.8 amps rather than 7.9 amps. In your example this could account for what you are seeing. I would need to see maybe 100 meter reads (to establish a mean) to see if this holds up.
We stand behind the kWh values that the meters report (in the case of the Omnimeters, all kWh values will be +/- 0.5% accurate). The amps data is too coarse to hold to +/- 0.5% on every read. The difference between 7.8 amps and 7.9 amps is pretty large.
Let me know if this makes sense,
Thanks,
Thank you for your questions.
As far as I understand, the meter samples volts, amps, and power factor at 25,000 times per second. It then takes these values to calculate kWh and at various moments of say a second (the values the meter passes to the RS-485 bus or to the LCD screen do not necessarily overlap from the same moment in time). You are correct that the formula is volts * amps * power factor.
Another thing that can happen is that the values are not rounded like you would assume. So if the meter is measuring 7.8789 amps, it will report it as 7.8 amps rather than 7.9 amps. In your example this could account for what you are seeing. I would need to see maybe 100 meter reads (to establish a mean) to see if this holds up.
We stand behind the kWh values that the meters report (in the case of the Omnimeters, all kWh values will be +/- 0.5% accurate). The amps data is too coarse to hold to +/- 0.5% on every read. The difference between 7.8 amps and 7.9 amps is pretty large.
Let me know if this makes sense,
Thanks,