CC vs Pulse accuracy

I am curious, what are the pros & cons of reading power with a CC vs Pulse.

- CC accuracy degrades with loads that are capacative or inductive?
- Pulse is more accurate for total, but would 2000 i/kWh be able to provide realtime power usage?

Anybody have both connected on the same circuit and ran a comparison?


gebhardm's picture

What is realtime? The FLM sends information on second base. That is on 2000 impulses per kWh a resolution of 2000 / 3600 Ws, so detects approximately 0.6 W per second.
Well, good enough, isn‘t it? The current clamps on the FLM2 are rather slow, 300ms accuracy, the ones on the FLM3 are faster. Also the measuring principle is different on the FLM3, as it is capable to set the readings in context with the current phase. So, you have to ask more precisely. Industry clamps are the state of the art... Make yourself aware of the measuring principle. Then you get your answer.

gebhardm's picture

I tricked myself; damn "Dreisatz" ;-) please excuse me being stupid; so again
1 kWh = 2000 imp
1000 Wh = 2000 imp
0.5 Wh = 1 imp
0.5 * 3600 Ws = 1 imp
1800 Ws = 1 imp
So, a load of 1800 W for 1 sec results in one pulse.
This means the limit what to "see", when measuring in 1 sec intervals; for 18W so you have to wait 100 sec to "see" it; still it says by the time between pulses that the average load was that, 18W during the last 100 sec.

Clamps "read" current; for example, 0 to 50 A are read as voltage equivalent at the FLM clamp port. Resolution is 10 bit, so per bit you get 50A/1023 = 0.05A; at a net voltage of 230V that is around 230V*0,05A = 11W per bit - theoretically. The sampling happens a little more sophisticated, but with a "speed" of 300ms you get maximally 3 valid readings per second (FLM3 clamps are faster); voltage is assumed constant for the FLM2, and detected for the FLM3. Alternating current is "funny", as power consumption is not only "real", but is a product of voltage and current in its phase relation, bringing into concern to get all parameters for calculating the correct power consumption or supply - the FLM3 has a lot of corresponding values on its MQTT channel, including voltage and phase shift. Wikipedia is your friend on all the math behind.
Long text, short answer: For "realtime" measurement there is a good rationale why current clamps are used when noninvasively trying to measure power; for the FLM2 the possibilities are limited, the FLM3 is here way better - and with that, for inductive loads requiring to bring the phase shift of current and voltage into the measurement and colculation, impulse counting has proven to be more reliable, the FLM3, well, could be way better
And note, we are talking about an FLM for 200 Euros, not a Fluke for several thousands, so again "realtime" is rather relative and depends heavily on the software part to bring all parameters detected into context, not to mention the accuracy of parts.