[Amps] Volt-watt meter

[Gary Schafer]

Hi Will,

I would think you could get close enough using the resistor with 
resistive loads. Probably as close as the cal lab would get you for an 
analogue meter.
Problem may be that reactive loads may not come out the same??
But I would try the series resistor and see what you get.
Do you have a good digital meter like a Fluke or HP with good ac specs?

I am not sure how close to advertised wattage light bulbs are but I 
would think not all that close.

73
Gary  K4FMX


Will Matney wrote:
> Gary,
> 
> That's exactly what I was thinking and still wouldn't be really for sure on 100% accuracy. Really, a few percent off wouldn't be that bad for what its intended purpose was for. However, one would like to be as accurate as possible too. I bought this to measure the wattage on transformers after they were built ( load and no load ). My guess is that those bulbs aren't too accurate on their ratings, or they rated them at 120 volts, and the line was a little lower. To be honest, without digging the meter out, I cant recall the maximum readings, but I think on low, it went to about 1 kW and on high maybe 3.5 kW. I'll try to dig it out later today and see.
> 
> Thanks,
> 
> Will
> 
> *********** REPLY SEPARATOR  ***********
> 
> On 4/22/05 at 10:43 AM Gary Schafer wrote:
> 
> 
>>What is full scale power of the meter?
>>
>>You could use a precision resistor in series with the load and measure 
>>the voltage across the resistor to get current. However keep in mind 
>>that most ac voltmeters don't do a very good job. If you get with in a 
>>few percent you will be doing good.
>>
>>73
>>Gary  K4FMX
>>
>>
>>Will Matney wrote:
>>
>>>I have a Simpson volt-watt meter here I'm thinking about getting
>>
>>calibrated. The thing is, I'm not really sure how accurate it is. After I
>>bought it, I tried it out on a lamp in the house using a 100 watt buld.
>>Something didn't jive about the watt reading when I calculated the wattage
> 
>>from the line voltage shown as the meter showed a lower wattage. I wonder
> 
>>just how accurate those bulb ratings are? Simpson is known for good
>>accuracy because of their meter movements, but I'm not too sure about
>>this. I'd like to test it again before I pay a fortune for calibration on
>>it. I thought of using a transformer but then your not sure what the power
>>actually is due to losses. I don't have any power resistors large enough
>>handy to at least get a 1/2 scale reading. What might be a good circuit
>>I'm not thinking of to test this? Note; this meter is designed for power
>>readings on a 120 or 240 Vac line.
>>
>>>Thanks,
>>>
>>>Will
>>>
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>>
>>
>>
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> 
> 
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