A method for reading current...the clamp meter. - AVS Forum
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post #1 of 20 Old 01-28-2013, 04:48 PM - Thread Starter
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Here is a very short video that shows how to measure current in an AC line.

Enjoy.

Listen. It's All Good.
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post #2 of 20 Old 01-28-2013, 05:24 PM
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It is called the "amp probe" from electrical techs
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post #3 of 20 Old 01-28-2013, 06:05 PM
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I used to have one of those years ago, until I loaned it out to my father and he lost it somewhere. frown.gif

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post #4 of 20 Old 01-30-2013, 12:35 PM
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would this http://www.amazon.com/Sinometer-UT202A-Auto-ranging-Clamp-Meter/dp/B005FSSKJA/ref=sr_1_1?ie=UTF8&qid=1359578151&sr=8-1&keywords=clamp+meter be accurate enough to measure how much currents going into your speakers, and then you could use a volt meter with it and you could find exact power draw of your speakers?
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post #5 of 20 Old 01-31-2013, 03:49 AM
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Quote:
Originally Posted by WagBoss View Post

would this http://www.amazon.com/Sinometer-UT202A-Auto-ranging-Clamp-Meter/dp/B005FSSKJA/ref=sr_1_1?ie=UTF8&qid=1359578151&sr=8-1&keywords=clamp+meter be accurate enough to measure how much currents going into your speakers, and then you could use a volt meter with it and you could find exact power draw of your speakers?
clamp meters are great for measuring constant current. not so for currents that spike all over the place.

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post #6 of 20 Old 01-31-2013, 06:49 AM
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600 A? Should cover most home products... smile.gif

No BW specified; these tend to target AC lines and may not have much bandwidth, and probably not the resolution desired for audio applications. A large clamp needs a pretty good field (high current) to register.

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post #7 of 20 Old 01-31-2013, 07:10 AM
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Quote:
Originally Posted by paskal9 View Post

clamp meters are great for measuring constant current. not so for currents that spike all over the place.
+1. They're used by electricians at the service breaker box to test how much load is being drawn on each circuit, to be sure than they aren't running too close to the breaker capacity.

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post #8 of 20 Old 01-31-2013, 07:31 AM
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could you run a sin wave on an amplifier and then measure the current draw of the amplifier power cord?
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post #9 of 20 Old 01-31-2013, 10:06 AM
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That or use a Kill A Watt or similar device, only problem is you need to know the exact efficiency of you amp to calculate power output.
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post #10 of 20 Old 01-31-2013, 02:34 PM
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Quote:
Originally Posted by mtg90 View Post

you need to know the exact efficiency of you amp to calculate power output.
If that's the goal measure the output voltage and use ohms law to calculate power.

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post #11 of 20 Old 01-31-2013, 07:53 PM
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You measure the resistance of the load (speaker) in ohms, then run a constant test tone and measure AC volts. The current is your voltage measured divided by the resistance.
I prefer any product made by fluke, they hold there specifications, typically other branded meters will require alignments after 12-16 months to maintain their specs. FYI, I have calibrated that very Extech clamp meter shown in video. Those are defiantly junk and have seen them fail right out of the box.
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post #12 of 20 Old 01-31-2013, 08:06 PM
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Quote:
Originally Posted by Kiel'thalin View Post

You measure the resistance of the load (speaker) in ohms, then run a constant test tone and measure AC volts. The current is your voltage measured divided by the resistance.
I prefer any product made by fluke, they hold there specifications, typically other branded meters will require alignments after 12-16 months to maintain their specs. FYI, I have calibrated that very Extech clamp meter shown in video. Those are defiantly junk and have seen them fail right out of the box.

I'd hope so, flukes are 5-6x as much as others biggrin.gif
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post #13 of 20 Old 01-31-2013, 08:23 PM
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Originally Posted by WagBoss View Post

I'd hope so, flukes are 5-6x as much as others biggrin.gif
Fluke model 115 will suit most home applications, those fancy ones are the ones you want to stay away from.
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post #14 of 20 Old 01-31-2013, 09:09 PM
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I'll tell Agilent the 8-digit DMM I am using can be replaced by Fluke's handhelds... smile.gif

The problem with Ohm's Law in this case is that speaker impedance tends to vary wildly with frequency so calculating power gets tricky.

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post #15 of 20 Old 01-31-2013, 09:15 PM
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You need only measure the driver's impedance with a woofer tester or DATS and use the impedance at the frequency you are running the sine wave at. The real problem now is how impedance changes under higher cone excursion which is much much harder to measure.
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post #16 of 20 Old 02-01-2013, 05:56 AM
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Quote:
Originally Posted by DonH50 View Post

The problem with Ohm's Law in this case is that speaker impedance tends to vary wildly with frequency so calculating power gets tricky.
Only if you're trying to find the power at individual frequencies, and I don't know what you'd want to do so. If all you're interested in is a ballpark average figure measure the voltage with a peak hold meter and calculate the power using the speaker nominal impedance.

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post #17 of 20 Old 02-01-2013, 07:17 AM
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WagBoss asked how to get the "exact power draw" of his speakers. I am not sure what that means exactly... smile.gif If he really wants exact, then he needs the ability to measure current and voltage, or he has to know the signal BW and speaker impedance and so forth. In any event, I think the main point to be made is that a high-current clamp current meter designed for industrial use is not an appropriate measuring tool for this application.

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post #18 of 20 Old 02-01-2013, 07:40 AM
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Quote:
Originally Posted by DonH50 View Post

WagBoss asked how to get the "exact power draw" of his speakers. I am not sure what that means exactly... smile.gif If he really wants exact, then he needs the ability to measure current and voltage, or he has to know the signal BW and speaker impedance and so forth. In any event, I think the main point to be made is that a high-current clamp current meter designed for industrial use is not an appropriate measuring tool for this application.
+1. IMO he's not aware that power varies with current, current varies with impedance, and impedance varies with frequency, so you may be drawing 10 watts at one frequency, 500 watts at another, yet with the same SPL at both. Strictly speaking this isn't something we really concern ourselves with. From a practical standpoint all that matters is current draw at the speaker's lowest impedance, and being sure that the amp is capable of handling that load.

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post #19 of 20 Old 02-01-2013, 07:58 AM
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Originally Posted by Bill Fitzmaurice View Post

+1. IMO he's not aware that power varies with current, current varies with impedance, and impedance varies with frequency, so you may be drawing 10 watts at one frequency, 500 watts at another, yet with the same SPL at both. Strictly speaking this isn't something we really concern ourselves with. From a practical standpoint all that matters is current draw at the speaker's lowest impedance, and being sure that the amp is capable of handling that load.

lol? i wanted to know if it could read current in speaker wire so I could test the impedance at certain frequencies in speakers... for fun smile.gif
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post #20 of 20 Old 02-01-2013, 09:11 AM
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Originally Posted by WagBoss View Post

lol? i wanted to know if it could read current in speaker wire so I could test the impedance at certain frequencies in speakers... for fun smile.gif
Do an impedance sweep, it's a lot easier.

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