D
Dave Martindale
- Jan 1, 1970
- 0
I recently bought a UPM EM-100 "electronic energy meter" ($25 at
Canadian Tire). It measures line voltage and current drawn by whatever
is plugged into it, calculates "watts", and records max current, max
"watts", operating time, and the integral of watts. It will also
convert watts to dollars if you tell it your energy rate. It looks like
this:
<http://www.upm-marketing.com/produc...Rn=484&3O^_:29VU[^RP=[Y6"6N"W^L &item=")0< >
Internally, it just uses a shunt to measure current; there's no current
transformer. The circuit is battery-powered and connected directly to
the line. Current range is 0-15 A with 0.01 A displayed resolution. I
compared it to my best handheld meter connected in series with the load,
and the EM-100 reading agreed within a percent or two of the "serious"
meter.
However, it seems that it really measures volt-amps and calls that
"watts". I plugged in an unloaded isolation transformer, which would
have had a very low power factor (almost pure inductive), and the
measured current was quite accurate, but the displayed "watts" was
simply the product of current and voltage. So this unit should work
well for high power factor loads, but it will be quite inaccurate for
low power factor loads.
The most commonly recommended device for measuring appliance energy
consumption seems to be the "Kill-A-Watt". It does distinguish between
watts and VA in display, and can also display power factor. But is it
accurate for low power factor loads?
Dave
Canadian Tire). It measures line voltage and current drawn by whatever
is plugged into it, calculates "watts", and records max current, max
"watts", operating time, and the integral of watts. It will also
convert watts to dollars if you tell it your energy rate. It looks like
this:
<http://www.upm-marketing.com/produc...Rn=484&3O^_:29VU[^RP=[Y6"6N"W^L &item=")0< >
Internally, it just uses a shunt to measure current; there's no current
transformer. The circuit is battery-powered and connected directly to
the line. Current range is 0-15 A with 0.01 A displayed resolution. I
compared it to my best handheld meter connected in series with the load,
and the EM-100 reading agreed within a percent or two of the "serious"
meter.
However, it seems that it really measures volt-amps and calls that
"watts". I plugged in an unloaded isolation transformer, which would
have had a very low power factor (almost pure inductive), and the
measured current was quite accurate, but the displayed "watts" was
simply the product of current and voltage. So this unit should work
well for high power factor loads, but it will be quite inaccurate for
low power factor loads.
The most commonly recommended device for measuring appliance energy
consumption seems to be the "Kill-A-Watt". It does distinguish between
watts and VA in display, and can also display power factor. But is it
accurate for low power factor loads?
Dave