Author Topic: wattmeter needed  (Read 1391 times)

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Offline Wytnucls

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Re: wattmeter needed
« Reply #25 on: September 26, 2020, 08:08:47 pm »
Well, that's fortunate. Hopefully, that's all you will need!
Extech doesn't make anything. They slap their name on all sorts of meters from other brands.
 

Offline mjkuwp

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Re: wattmeter needed
« Reply #26 on: September 27, 2020, 01:30:47 pm »
Athough you can technically, mathematically, 'RMS' anything, I don't think you want 'RMS watts'.
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member bdunham7 has the correct position and the entire post is good.
https://www.eevblog.com/forum/testgear/wattmeter-needed/msg3250004/#msg3250004


My interpretation is that you desire instantaneous readings of Volts and Current (multiply to get power). and you want this done at a very high data rate.  I understand the desire for high quality measurements but still I don't see any reason RMS comes into play here.

Another idea from left field is to use an analog multiplier with a high bandwidth and put your meter at the output of this.  Parts such as AD633 will do this.

https://www.analog.com/media/en/technical-documentation/data-sheets/AD633.pdf

and there is a brief explanation of a project here:

https://www.circuitspecialists.com/blog/measuring-power-with-a-digital-panel-meter/

maybe there are some dev boards or other projects that would be available for purchase.

 

Offline eevcandies

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Re: wattmeter needed
« Reply #27 on: October 01, 2020, 03:54:55 pm »
I don't want it "instant" (2-3 readings a sec is fine) I just want to  multiply RMS volts times RMS amps to get VA , or Watts, if the power factor is near unity.    That's the standard equation.  So a dual multimeter that measures both should be able to do the trick (since I do the same thing using two rms meters and a calculator).
 

Offline mjkuwp

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Re: wattmeter needed
« Reply #28 on: October 08, 2020, 01:13:49 pm »
I think Dave's 121GW meter does this with a 3-wire connection.
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The meter you mention looks pretty interesting...I wish it gave selectable watts rather than just VA (since it monitors both I & V in one unit, it should be able to measure watts)..well, it's close!   I wonder if there is one that measures output as well, this is for power supply efficiency testing (input & output power)..could use two of these meters, perhaps.

I guess I am not sure what you are after then because some statements don't go together.

The units of V*A is Watts and 1 Volt x 1 Amp == 1Watt so if you don't care about power factor and want to assume a purely resistive load then this meter would do that.  The display might have an indicator stating VA or mVA but you can read this as Watts.

The quantity you would be measuring I think is Apparent Power as opposed to Active Power because it is not accounting for phase differences between the waveforms.

It could be helpful if you share with the group what you are trying to achieve - what is the outcome you want.  It could be an interesting discussion; I think context always helps when discussing tools.
 


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