Accuracy of 60Hhz power measurement device on 50Hz AC

Without more information, anything anyone could say here would be mainly speculation. I'd look into finding someone who has a real power meter and just doing a comparison; that should tell you if it's close enough or if you need some kind of calibration chart.

Good Luck! Rich

On the balance of probabilty ( and likely technology used imho ) I'd expect it to be fine but you'll need to confirm that some way.

Graham

What would be a *safe* way to do this with 230VAC? The last time I even tried to measure the actual local voltage with a DMM, I caused a trip :P I'd hate to think what might happen (or more likely explode) if I try to hook a couple of resistors and capacitors to the mains.

Alternatively, if the proper method is beyond me, would it be reasonably close enough to approximate by using say 3 switching power supply?

E.g. 1 without PFC, 1 with passive PFC and 1 with active PFC and determine if the values are close enough to expected? Since I think A-PFC should be in the 95~99 range while P-PFC should be around the

Hmm, well, say if you would to design a device to measure PF at voltage ranges from 80V to 250VAC for 60Hz cheaply, how would you design such a device and what would you expect to happen to accuracy if the frequency drops to 50Hz? I guess that's what I'm looking for, i.e. theoretically, would the most likely implementation of such a device be affected by the frequency of the input? Or would the typical method of measuring PF render the frequency a non concern?

Kind of like if a person designs a switching PSU with active PFC it appears that it doesn't matter anymore if the incoming voltage is 115 or 230 nominal. So it wouldn't really matter if the PSU was connected to a 160Vac supply, as opposed to a PSU was designed for 115Vac without PFC which would blow up the input caps if connected to 160vac.

I can't think how yoou managed that, set your meter to ac volts and plug the propes correctly then put the probes on power terminals (not on earth) it should work unless there's a fault in your meter.

probably the best way is to set the circuit up with the meter attached and then turn the power on.

an unloaded transformer (one with nothin connected to its output) is going to have near 0 power factor, and if you can measure the current you can combine it with other resistive loads to get different power factors.

then put mains-rated resistors of different sizes in parallel with it (eg: soldering iron, heater on low, heater on high...)

probably not extremely accurate as the PF on those varies with load,

Bye. Jasen

if it's done with a microcontroller and digital-to-analogue converters accuracy will probably decrease for higher frequencies, but there may also be lower frequency limit where the device stops behaving sensibly.

I doubt that going from 60 to 50 Hz would mess it up much, but it's possible that some of the devices internal workings, or the computation algorythm is designed specifically for a 60 HZ supply...

Bye. Jasen

(snip) Besides just being clumsy with the probe tips, the most common way to blow up a meter is to check line voltage with a meter set to a current range. Many ohm meters also blow up with 230 volts across the leads.

Ok, I think THAT's the problem. I thought one end goes to ground (earth) and the other.... :p

Hmm, ok so I just need to buy one of them naked transformer coils and hook one end to live, one end to neutral and I should get some current readings but 0 PF?

Then I add some resistors in series to it? And use the previously mentioned R, F, C formula?

Thanks.

Before you can also measure the DC-resistance of the primary with your multimeter and take that into account for your reference reading. Be careful with your meter, set the AC current range to 1A first, and switch off the power each time you change the range. When you switch the meter when power is still connected and current flowing, an inductive spike might destroy that switch.

be real careful when connecting meters to the mains, if you don't have the meter corrrectly configured (set to the a high enough voltage range etc) you can damage it (unless it's a real expensive model).

You may well have something suitable already.

it doesn;t need to be "naked" a transformer type wall-wart would do. (typically these are the heavy ones), or other mains-transformer based powersupply (battery charger, model train controller, 115V step-down transformer, isolating transformer, arc welder....) with nothing attached to the output they'll behave almost exactly like bare transformer wich should look pretty much like a pure inductancd (PF near zero)

this is the sort of thing that could be done using one of those plug-boards and plugging different loads into it...

yes...

Bye. Jasen

...

Jeez, John, who pulled your chain?

This is sci.electronics.basics. Please act like a grown-up.

Thanks, Rich

It might or might not matter - it depends a lot on what's inside your power factor meter. You still haven't said how it connects to the line and equipment - do you plug it into the wall, and plug your device into an outlet on its face, and the meter reads out the power factor of the device? For power factor, you have to measure both the voltage and current, and their phase.

So, how are you supposed to connect this device? Do you have a picture of it?

Thanks, Rich

It's like a Watts Up meter, exactly the way you described it. A rectangular piece of equipment, one side fits into the wall socket, plugs whatever I want to measure on the other side. There's a display and a row of buttons for selecting the mode i.e. Frequency, Voltage, KWh, Watt, VA and PF. I'm guessing the easiest way to get PF since they can read Watt and VA would be simple division of the two right?

I'd think the easiest would be to turn the switch to the "PF" position. :-)

Good Luck! Rich

Bleahz, I'm not that dumb yet!!! :P

WHat I meant was the easiest way for the device designer/programmer would had simply been to take the watt and va figures instead of making some more circuitry to measure the PF. So if I can determine the accuracy of the watt and va readings, that should also allow me to tell if the PF reading is accurate no?

i.e. by hooking up a purely resistive load to the meter, I should get X va and X watt and the PF should read 1. If any of these don't turn up the expected way, the meter's not accurate, right?

Absolutely:

Power factor is defined by IEEE and IEC as the ratio of true power to apparent power:

PF = W/VA.

if that doesn't work the meter has firmware problems. I expect it does the same arithmetic you plan to, internally.

a better test may be putting an inductive load on the meter and then a resistive load, and then both, and confirming that the W an VA figures add up correctly. (or close enough)

repeat with different loads until you are confident that it's working (or not)

Bye. Jasen