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# Analogue Ammeter

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I am using an analogue ammeter to make current and voltage measurements. The analogue meter utilizes and electromagnet; it is not heat based. I am curious if their is a bandwidth for which this type of meter is accurate. I know that digital, hand- held multi-meters have bandwidths that are usually limited to between 40 Hz and 100Hz.

David

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What exactly are you trying to measure?

If the frequency is above the range of the meter, use a bridge rectifier to measure the current/voltage, and a oscilloscope to measure frequency.

If the voltage is too high, use a voltage divider.

If the current is too high, calculate it based on known current at a known voltage (this may not be possible), to get the resistance of the load, then check the operating voltage to calculate the current.

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I do not see how a bridge rectifier solves the problem of a limited bandwidth for accurate measurements of a multimeter. The reason is that when you rectify the voltage or current the voltage or current still oscillates however now its polarity is constant. Therefore, I think that a common digital multimeter,which has a bandwidth of 40 to 100 Hz, is still unable to make accurate measurements of the voltage or current of this device. In fact, don't multimeter rectify the voltage or current on their own; this is why they have the AC measurement option.

I look forward to hearing your reply.

Thanks for your response.

David

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Well, the idea I had with rectification was to convert AC to DC, and then measure the DC voltage, thereby getting around the bandwidth issue.

If you are working with tesla coils (I'm guessing so) there are certain formulas to get the voltage on the power circuit side.

I think the tank cap needs to be 2x supply current + safety margin (usually 30kV+ for neon sign transformers).

Standoff between turns on the primary coils can be calculated using the breakdown voltage of air.

There are formulas to calculate the voltage across the secondary coil, and from there you can get volts per turn to know the amount of insulation needed for the wire.

For actual electrical data, I'd recommend an oscilloscope with a high voltage probe (basically a voltage divider that measures electrical field).

I'd recommend this site:

http://www.hot-streamer.com/

It's run by one of the main contributors to the Tesla Coil mailing list I posted...somewhere.

Paul Nicholson's site (linked from the above web page) has a bunch of differen modeling software that makes it pretty easy.

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