Old EON clamp meter - any use?

Why not just carry on using it ? More reliable, and foolproof than most IHDs ?

Is it a rebadged "Owl" device? May look different from their current offerings ...

IIRC you needed a TTL-level USB dongle, then it would spit out XML readings you could do whatever with them ...

It has the USB dongle to spit out data. It has been a while, though.

Doesn't look like any of the Owl pictures.

This is it.

Cheers

Dave R

Looks kinda familiar to what I had, think I gave it to dad, he must have binned it as I didn't see it when clearing his house.

Use putty to open the relevant COMx: port and see what shows up at the standard speeds. I think they did come with some software?

Yup it should work on individual circuits...

Two things to keep in mind; you need to clamp round an individual conductor, not a whole cable (otherwise it will see the vector sum of the current flow in Line & Neutral, and read zero (and if it does not read zero, you might have more pressing problems!))

The scaling might be set to give a decent resolution in the 0 to 100A range, and that might be a bit large for the typically much smaller loads of a single circuit. However you can work round that by looping multiple turns of the wire under test through the clamp. e.g:

Does it really measure Watts or is it VA? I don't see any mention of Power Factor anywhere. Its probably not too important for the whole house but for smaller loads it can result in huge errors....

Dave

It probably measures amps and if it automatically converts to "watts" it is by assuming the voltage; so VA.

It does not have any way of capturing the voltage waveform, only the current. So it will have to make assumptions. Probably good enough to get a feeling for whole house consumption - but less so for lightly loaded circuits with many low pf loads.

My quick and dirty hacked together power meter needed to capture the voltage waveform and the current one in real time to be able to give a more accurate report:

Once you have a microcontroller involved its is fairly trivial to measure either

Sample the voltage and current waveforms say 1000 times a second, multiply each sample pair and shove the result in a ring buffer of say one mains cycle (20 samples) length and average it. That's your watts.

VA is the multiplicand of the average value of the current samples , converted to positive and the average value of the voltage similarly treated.

Latest PIC type chips could so that more like 10,000 times a second easily

Not if it is digital. As mentioned above, it is trivial to sample voltage and current many times a cycle and do a simple calculation to get watts

Yep, and if the unit is powered by an wallwart with AC output rather than DC then you can get the AC waveform in a convenient way that's no different from any other low power device.

Power monitoring chips do all of this stuff at about 20kHz in a simple cheap chip. ADC accuracy is pretty good too (12+ bit?).

Theo

Not so easy to measure the voltage if the only input you have is the output of a current transformer though...

Good to hear. Of course if they are in fact main powered nothing easier than to pick off the ac voltage waveform one way or another. Optocoupler maybe safest

Very vague memories but I think the software was for XP or Vista or something and not easily available on W7 onwards.

Cheers

Dave R

Well true; but try sampling voltage with a clamp meter with no conductive connection to the wiring!

Well, RMS values for preference. But one can be derived from the other if you assume a sine wave.

Well its not hard really to pick up the wave form, If the meter isn't mains fed you just have to guess at the voltage...

The point being with multiple kHz sample rates you don't need to assume

Its not the shape, its the current/voltage phase mis-match. In the past I would have expected the typical household load to be inductive.

So you had light bulbs, things which got hot such as kettles, irons, toasters and ovens, electronic devices which had linear power supplies with a big transformer and the odd motor in say a hoover....

.. these days most light bulbs are LED so may have capacitive droppers although these are now less common but legally can have a power factor as low as 0.5. So the VA or apparent wattage is twice the actual wattage...

.. then electronic devices. you would be hard pushed to find an electronic device without switched mode PSU which again can have a power factor as low as 0.5, so a 25w laptop charger would look use up to 50VA.

Even the fridge or freezer may have an inverter controlled motor so a switched mode PSU and an inverter to provide a variable frequency drive to control the speed of the fan.

Because a simple clamp meter can only measure current, its pretty useless at measuring power in a modern home. You need to know the voltage across time, take multiple samples across time and total the results. If the power factor is 0.5 your clamp meter will read 50% high.

For modern devices in standby the power factor can be even higher.

... this mass of switched mode power supplies is also the reason its pointless, from a power saving point of view, to unplug phone chargers and similar when not in use. Switched Mode power supplies use very little power when there is no load on them. My power monitor plug which claims to measure down to 1/100th or a watt of load shows zero when I unplug the charging lead from laptop, or plug a disconnected phone charger into it....

Dave