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Tim in Phoenix
Joined: 21 Oct 2006
Posts: 4409
Location: Phoenix
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| Posted: Mon Aug 23, 2010 11:06 pm Post subject: What Value Resistors for a Voltage Divider? |
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Guys!
I am working on a projector with a weird problem; the blue G2 keeps spiking above the limit of my Fluke meter, possibly as high as 1000 vdc. So I want to feed the G2 thru some resistors to ground, and sample G2 safely into the meter. What resistor values would permit this?
I was thinking G2>------<9 meg>--------Fluke in--------<1 meg>-------- >Ground
This should take 1000 vdc and divide x ten, right? The Fluke should be seeing from zero to 100 volts.
What would you recommend? I want to protect the Fluke and the HVPS. Should I ground to the frame or another point?
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garyfritz
Joined: 08 Apr 2006
Posts: 12088
Location: Fort Collins, CO
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| Posted: Mon Aug 23, 2010 11:23 pm Post subject: |
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9M + 1M will divide by 10. I can't tell, are you putting your Fluke in series with the resistors, between the 9M and 1M? That won't work. If you've got one lead of the Fluke between the 9M & 1M, and the other lead on ground, you should get a 1/10 reading.
I have no idea if 10M to ground will affect the G2. Probably not.
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tse
Joined: 03 May 2006
Posts: 1014
Location: Sweatbucket, Fl.
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| Posted: Mon Aug 23, 2010 11:44 pm Post subject: |
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Are you sure the input resistance of your meter is 1M? I believe most are 10M.
The Marquee G-2 (you didn't say which projector) output is capable of 100uA. That is equivalent to 10M at 1000V. There is a 16M (or is it 22M?) resistor on the neck card so the lowest value that you can put across that resistor and draw less than 100uA at 1000V is 27M.
If you put 20M (like two 10M in series) in series with your meter you won't overload the G-2 output. Just multiply meter reading by three. Assuming your meter is 10M input.
Scott
_________________
"Were we directed from Washington when to sow and when to reap, we would soon want bread."
Thomas Jefferson
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Tim in Phoenix
Joined: 21 Oct 2006
Posts: 4409
Location: Phoenix
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| Posted: Mon Aug 23, 2010 11:52 pm Post subject: |
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Hello
The meter won't handle over 660vdc, so I wanted to read the G2 in a safer mode.
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tse
Joined: 03 May 2006
Posts: 1014
Location: Sweatbucket, Fl.
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| Posted: Tue Aug 24, 2010 12:00 am Post subject: |
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With 20M in series with your meter 1000V will read 333.3V.
Scott
_________________
"Were we directed from Washington when to sow and when to reap, we would soon want bread."
Thomas Jefferson
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Tim in Phoenix
Joined: 21 Oct 2006
Posts: 4409
Location: Phoenix
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| Posted: Tue Aug 24, 2010 12:12 am Post subject: |
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Guys!
I have some 22 meg resistors here, I put five in series and will try reading between the fourth and fifth resistor, the fifth resistor going to ground. The meter reading times five should be the G2 actual voltage.
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tse
Joined: 03 May 2006
Posts: 1014
Location: Sweatbucket, Fl.
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| Posted: Tue Aug 24, 2010 12:30 am Post subject: |
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Meter reading x 13.8 = input voltage. Placing your 10M meter across the bottom 22M resistor makes the value 6.875M.
Scott
_________________
"Were we directed from Washington when to sow and when to reap, we would soon want bread."
Thomas Jefferson
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