Real Power and Apparent Power

I have a cheap, non-logging meter which measure the current only, and the voltage is set as a configuration item. I expect Flukso to do the same.
The Flukso will therefore measure apparent power (VA), rather than real power (W). Measuring the standby power of my home appliances with a "Powermate Lite" has shown that many have a poor power factor. It looks like the base load of my house is about 180W but 250VA. When I turn on the fluoro lights, or the fridge runs, it doesn't get any better.

I would like the Flukso to measure real power, however this would require a major change to the sensor.

icarus75's picture

Hi Ghostgum,

You can find a benchmark of a 1-phase and 3-phase Fluksometer against a DIN-rail energy meter with pulse output in this blog post. You're right when it comes to a current clamp measuring apparent power. In our live test of a typical household, the deviation is limited to a few percent. Furthermore, new appliances have to conform to certain power factor requirements which limit the deviation of VA to W.

Using a split-core current clamp as a sensor is a good trade-off between measurement accuracy and ease of installation/safety. We actually used DIN-rail energy meters in our alpha trial. They proved to be a real installation burden. Either people didn't have a DIN-rail type of fuse box, the fuse box would have no spare slot available or the empty slot would be a pass through for other cabling. Even when a free DIN-rail slot was available, we'd still have to re-route the mains via the energy meter. No small feat, when non-braided cable had been used during initial installation.

If you really require sub 1% measurement accuracy, you can use a DIN-rail type energy meter. The Fluksometer has three (internal) digital inputs available which readily accept the open-collector output of the energy meter's pulse output when it conforms to the IEC61036 standard. No additional circuitry required. More information on the digital input ports 1-3 can be found in the same blog post. Keep in mind that you'll be re-wiring 230V-240V cables! We strongly advise you to consult a qualified electrician.


polken's picture

Hi Bart,

You obviously didn't anwer Ghostgum's question which was about measuring REAL power thus taking into account the power factor. (,

However a solution could be provided in the form of a small optional module containing 3 Four-Quadrant Multiplier circuits (eg. ) so the 3 voltages and currents could be applied via
voltage_dividers resp. your current clamps already provided.



icarus75's picture

Hi Mark,

I should have mentioned that DIN-rail energy meters measure real power. This means they are not susceptible to errors due to line voltage variations or power factor. So what I was really saying is that it is perfectly possible to measure real power with the Fluksometer by using a DIN-rail energy meter and connecting the pulse output to the Fluksometer.

Having the Fluksometer itself measure real power is not that straightforward. With the clamps we have a nice galvanic isolation between the fuse box and the Fluksometer. The S0 pulse output of a DIN-rail energy meter is opto-isolated. Both solutions thus provide a 'safe' way to measure electrical energy. If we have to measure line voltages as well, we would have to offer the 230V to the input of the Fluksometer. Hmmmmm. An alternative could be to have a separate measurement unit inside the fuse box, reporting measurements to the Fluksometer based on sampled line current and voltage. This would then typically be a DIN-rail compatible device for ease of installation. But such measurement units already exist. They're exactly the DIN-rail energy meters discussed above.