Watt meter

One thing that I forgot to mention that can these wattmeters work with 100KHz signals.

Thanks jess

"Jessica Shaw"

Post a direct link to the sale.

.... Phil

There is no item number in that link. It is only veiwable from your account.

Post it like this:

by replaing the string of x with the item number to give you alink like this:

Just copy & paste it over the row of x's

signals.

The Simpson meter is only calibrated for 60 Hz loads. The inductance in the metering circuit is way too high for 100 KHz.

You're looking at silly money for one that will do that - in days gone by, such wattmeters used a device which combined a filament lamp & thermocouple in the same envelope, some of those were good up to RF.

Unless you're filthy-rich, you may need to look at home made - at least one hobby magazine has published a design that uses modern solid state measuring chips to determine power in a load - IIRC it may have been Elektor, and there's probably at least a PCB available from readers services - if not a full kit.

signals.

You can calibrate them to work. That doesn't make them precise, however.

For 100 kHz signals, I'd use an analog multiplier, or a two-channel digital oscilloscope and some math. The input impedances of your current and voltage probes, of course, have to be compensated.

"Ian Field"

... Phil

That's the way I measure power factor. You need a digital 'scope that multiplies and integrates.

RMS volts * RMS current = apparent power.

Per sample volts * per sample current, integrated over a cycle = true power.

"Fred Abse"

1. RMS voltage squared / resistance = true power.

2. RMS current squared x resistance = true power.

Important to check that over the frequency range of interest, the resistance value is constant.

Also, the wave must be cyclic and non varying over the test period.

Plus any DC component must be included in the RMS value.

... Phil

A log/antilog amplifier circuit can be used for a multiplier:

Another method that works from 1kHz to over 1 GHz:

There's an RF wattmeter kit here for $55 (and some other interesting = items):

And you can probably use something like the dsPIC30F2010 which has six=20

Paul=20

Quite so.

Phil Allison Inscribed thus:

What Jessica needs is a "Bolometer" ! Though I haven't seen one for many years. They look a little like the old 954 acorn valve.

ITYM a calorimeter

Jasen Betts Inscribed thus:

Yes you're probably right. It must be 45-50 years since I used them to measure RF power. Tiny little things, died at the drop of a hat. :-) About 20mw was the most they could handle. I've probably still got some hiding, in all the junk I should really throw out...

I used a bolometer mounted in a waveguide to measure power at X-band back in 1949. They couldn't take much more than a 50% overload without burning out and calibrating was tricky!