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Old 13th February 2004, 08:44 PM   #1
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Default Trimming resistors

Hello all,

I'm looking for a way to change or trim the value of a metal film resistor. Is this doable? By how much can you adjust the value?
I suppose you can trim a resistor only one way, up or down (if at all).

Any input is very welcome.

Thanks,

Jarno.
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Old 13th February 2004, 09:16 PM   #2
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One method is to put a slightly higher value in and then parallel a much higher value to 'trim' the final value.

Rx = 10 K.
install a 12K resistor and then add:

56K 60K 64K to get,
9.8K 10K 10.1K.

(this will add a litle bit of extra capacitance to the circuit)

If you are talking about removing the outside layer of one resistor then I believe you can only go up in value.
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Old 13th February 2004, 10:03 PM   #3
maylar is offline maylar  United States
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Bend it

Metal film resistors are the same basic composition as strain gages. Sensitive to mechanical stress.

Seriously... use a pot.
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Old 14th February 2004, 10:33 AM   #4
lucpes is offline lucpes  Europe
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Actually, there are two realistic options:

1) Buy a bunch of 5% tolerance resistors and measure them to get what you need. They're dirt cheap.

2) Use a trim pot if the wattage permits as maylar suggested.
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Old 14th February 2004, 12:11 PM   #5
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if you parallel with a larger resistor, the formula is:

Rnew = R1*R2/(R1+R2)
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Old 14th February 2004, 07:24 PM   #6
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Thanks for your replies. From your comments I gather that trimming a bit off the outside of resistors is no option? I would rather not use a trimpot so indeed parallel resistors is the way to go.

Thanks,

Jarno.
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