Accuracy at low power

[Automate]

I have read your FAQ about accuracy. It says:

"The ECM-1240 device is calibrated to within 1% accuracy. The CT accuracy must also be factored into the equation. Most of our CTs are accurate to within 1%. The overall accuracy is typically 2%."

I assume this is when the measured circuit is at full power. What about at a low power level? How many bits of resolution are the voltage and current inputs? How many samples are read per each AC sine wave?

Thanks,

[67stang]

Use this link to get to info on the CT's.

http://www.brultech.com/products/ECM124 ... /types.htm

In the right-half of the window, find the CT you want and under it's picture,
click on Specs. In the next window that pops up , you'll see -3- tabs ; click
on Specifications. Scroll down a bit and you'll see a graph showing the
% accuracy vs. amperage.

[Automate]

Thanks 67stang,

I'm interested in reading low power on a 20 Amp circuit. The smallest CT is the Micro-40. The accuracy chart for this CT only goes down to 1 amp or 120 Watts.

That's much higher than multiple LED light bulbs and even more so a wall wart for small electronics. I would like to know how much these small loads which may be running 24/7 are using.

And, the CT is only a part of the overall accuracy. According to this post http://www.brultech.com/home/community/ ... 8a2a6#p920
the aux inputs of the ECM-1240 are 10 bit resolution. They can measure up to 80 Amps so:
80 amps / 1023 = 0.0782 amps resolution which yields 0.0782 amps * 120 volts = 9.4 Watts resolution.

This means that anything below about 20 watts would have very bad accuracy and a wall wart at 4 or 5 watts may not register any reading.

[Teken]

Thanks 67stang,

I'm interested in reading low power on a 20 Amp circuit. The smallest CT is the Micro-40. The accuracy chart for this CT only goes down to 1 amp or 120 Watts.

That's much higher than multiple LED light bulbs and even more so a wall wart for small electronics. I would like to know how much these small loads which may be running 24/7 are using.

And, the CT is only a part of the overall accuracy. According to this post http://www.brultech.com/home/community/ ... 8a2a6#p920
the aux inputs of the ECM-1240 are 10 bit resolution. They can measure up to 80 Amps so:
80 amps / 1023 = 0.0782 amps resolution which yields 0.0782 amps * 120 volts = 9.4 Watts resolution.

This means that anything below about 20 watts would have very bad accuracy and a wall wart at 4 or 5 watts may not register any reading.

I just recently installed the new GEM module and also use micro 40 CT's. I have many low power devices and the GEM has no problem detecting their wattage in use.

Please refer to the screen shot listed below.

Teken . . .

[Automate]

Thanks for posting the data.

I wonder if the GEM is more accurate since it is a newer generation than the ECM-1240.

Also, just a reading does not tell us the accuracy. Do you have a Kill-A-Watt or other method of accurately measuring and comparing the power readings?

The Kill-A-Watt claims an accuracy of 0.2% and a maximum rating of 1875 VA or for a resistive loads, 1875 Watts. So 1875 * 0.002 yields plus or minus 3.75 Watts
http://www.p3international.com/products ... 00-ce.html

[Teken]

Thanks for posting the data.

I wonder if the GEM is more accurate since it is a newer generation than the ECM-1240.

Also, just a reading does not tell us the accuracy. Do you have a Kill-A-Watt or other method of accurately measuring and comparing the power readings?

The Kill-A-Watt claims an accuracy of 0.2% and a maximum rating of 1875 VA or for a resistive loads, 1875 Watts. So 1875 * 0.002 yields plus or minus 3.75 Watts
http://www.p3international.com/products ... 00-ce.html

Yes, I have two Kill A Watt meters for reference along with another *Blue Planet* device. I also compared the watt data to the manufactures listed power consumption. In all cases the GEM (measured power) was reflective of the makers claim.

As a data point: I have many various plug in *Insteon* devices. The maker claims aprox 1 watt of power consumption for these Appliance Linc modules etc. The GEM reports back the same level of power to the Kill A Watt etc.

Also, the GEM has a PT setting which allows you to *fine tune* the measured accuracy to portray the value captured. I have measured the incoming voltage to my main service panel and have adjusted the PT to accurately reflect the power being measured.

Teken . . .