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Old 12th Mar 2020, 9:33 am   #1
John M0GLN
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Default Mystery 'Capacity Divider'

These three photos were taken by a friend a few years ago, they are the only photos he has and whatever happened to the instrument is unknown.
It's called a 'capacity divider' and although I can't see it having anything to do with radios as such, the BNC socket labelled 10M, 12.5PF, 12.5PF suggests something electronic.

I wonder if anyone can identify this piece of equipment please?

Thanks

John
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Old 12th Mar 2020, 9:52 am   #2
Radio Wrangler
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Default Re: Mystery 'Capacity Divider'

It's a high voltage range extender for a voltmeter.

Charging a larger capacitor near ground via a smaller capacitor from the unknown voltage puts a calculable fraction of the unknown voltage on the larger capacitor.

Used because it's a lot more difficult to make reliable high voltage resistors than it is to make high voltage capacitors. Used for measuring high voltage AC, can be used on dc as a one-shot measurement but that's difficult.

The capacitance of whatever you feed it to and the cable are in parallel with the output capacitor and affect the accuracy, hence the design value is carefully labelled.

David
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Old 12th Mar 2020, 9:53 am   #3
rontech
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Default Re: Mystery 'Capacity Divider'

The rounded top cap and the heavily insulated lead with the croc clip suggest something for EHT testing. Also the socket labelled 10 ( megohm? )
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Old 12th Mar 2020, 9:54 am   #4
rontech
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Default Re: Mystery 'Capacity Divider'

Quote:
Originally Posted by Radio Wrangler View Post
It's a high voltage range extender for a voltmeter.

Charging a larger capacitor near ground via a smaller capacitor from the unknown voltage puts a calculable fraction of the unknown voltage on the larger capacitor.

Used because it's a lot more difficult to make reliable high voltage resistors than it is to make high voltage capacitors. Used for measuring high voltage AC, can be used on dc as a one-shot measurement but that's difficult.

The capacitance of whatever you feed it to and the cable are in parallel with the output capacitor and affect the accuracy, hence the design value is carefully labelled.

David
Our posts just crossed lol
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Old 12th Mar 2020, 10:07 am   #5
John M0GLN
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Default Re: Mystery 'Capacity Divider'

It never ceases to amaze me how quickly these questions regarding seeminingly obscure items get answered, thank you for your replies and satisfying our curiousity.

Thanks

John
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Old 12th Mar 2020, 2:00 pm   #6
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Default Re: Mystery 'Capacity Divider'

S'easy! We're some very obscure people!

David
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Old 12th Mar 2020, 2:03 pm   #7
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Default Re: Mystery 'Capacity Divider'

Don't tell me you're not going to put it is as a puzzle in some non-technical magazine as a puzzle "What do you think this is for?" sort of thing. With the label on the far side in the photo, of course.

The replies could be somewhat amusing.

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