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Re: [Phys-l] glassware needed

I have a lamp controller hooked to the halogen lamp standard by my desk.
I turned the light well down to a round current reading, and read the
following parameters from the inexpensive "Kill-a-watt 4400"
meter (Cheesy name! <$20)

Volts 122.4V
Amps 2.00 A
watts: 158W
va: 245 voltamps
Fx: 59.9 Hz
p.f. 0.64

Turned high, I read:
Volts: 122.2V
Amps: 2.48A
watts: 293W
va: 303 va
Fx: 59.9 Hz
p.f. 0.96

These look plausible for a microprocessor with an A/D that samples reasonably fast. would I check, without a calibrated wattmeter to hand?
Oh, I know: warm a fluid sample at high pf and another at low pf and check
if the delta t is proportional to indicated power input? :-)

Brian W

At 04:29 PM 1/1/2009, you wrote:
Make sure that the 'inexpensive' watt-meter can correctly handle non-
sinusoidal wave forms.
Triac's don't output sine wave by a LONG shot.

True RMS measurement are often NOT produced by cheap meters.

(Or so it has been in the past - maybe things are better now??)

On Jan 1, 2009, at Jan 1(Thu) 3:26 , Brian Whatcott wrote:

> a wattmeter is now so within reach that it would be a good accessory.
> This would enable a TRIAC dimmer to moderate the power,

Forum for Physics Educators

Brian Whatcott Altus OK Eureka!