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Do Radio Shack Trimmers react to heat?

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tom86951

New Member
I have two 0-10k trimmer pots from radio shack. Last night I set them to 1000 ohms each, while I was sitting in my air conditioned house. After installing them in my car as pull up resistors for sensors, they now read about 800 ohms each. Do they loose their stability based on ambient temperatures? Should I use precision resistors instead?
 

mvs sarma

Well-Known Member
Yes, they change. but not so much as in this case.
It appears the mistake is in using a 10K pot setting it to 1000 nearly 10%. you may use 2K pot and set it to 1K it might behave better.

How ever there will be change wrt temperature. It is called temperature coefficient of resistance and it changes from material to matrial.
 
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Mikebits

Well-Known Member
I have two 0-10k trimmer pots from radio shack. Last night I set them to 1000 ohms each, while I was sitting in my air conditioned house. After installing them in my car as pull up resistors for sensors, they now read about 800 ohms each. Do they loose their stability based on ambient temperatures? Should I use precision resistors instead?
Why would you use trim pots as pull up resistors? Why not use a simple fixed resistor?
 

Hero999

Banned
Agreed using potentiometers for pull-ups does sound silly.

Pull-up resistors aren't critical, if the schematic specifies 1k but you don't have that value, use the nearest value you have. It can probably be between 820R to 1k2 without any problems.
 

tom86951

New Member
Ok, I'll swap in regular resistors. I have no electrical training, so was just trying to make the circuit as precise as possible. Perhaps pull-up resistor was the wrong terminology. I have using it as part of a circuit to measure the output of a thermistor (to measure air temps in my motor). I have a dataq data logger that measures anaolog DC voltages. In order to log the thermistor, I grounded one lead of the thermistor and sent the other lead to the datalogging input. I also connected this lead to a regulated 5vdc through the "pull-up" resistor. My theory was that the more precise the resistance on that resistor, the more precisely I could calculate the resistance/temp at the thermistor. In the temp range I am measuring, the thermistor has about 50 to 1000 ohms, so I opted for a 1K pull up.
 

tom86951

New Member
By the way, will regular fixed resistors also change significantly in resistance based on temperatures? If a 1K resistor measures 1000 ohms at 70F, what might it measure in a 160F environment?
 

audioguru

Well-Known Member
Most Helpful Member
When RadioShack was still selling (they are gone now) over-priced poor quality stuff in Canada, I remember the no-name-brand trimmer pots. I never tried them.
Instead I bought top quality name-brand (Bourns) trimpots from a real electronic parts distributor (Digikey or Newark) for less cost.
 

Hero999

Banned
Perhaps pull-up resistor was the wrong terminology. I have using it as part of a circuit to measure the output of a thermistor (to measure air temps in my motor).
That's an entirely different matter.

The correct terminology is "I'm using the resistor as part of a potential divider". In that case it does make a difference and pots have the advantage of being adjustable.

By the way, will regular fixed resistors also change significantly in resistance based on temperatures? If a 1K resistor measures 1000 ohms at 70F, what might it measure in a 160F environment?
It's not normally significant.

How accurate does it need to be?


Use 1% a metal film resistor rather than a 5% carbon film resistor.
 
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BrownOut

Banned
When RadioShack was still selling (they are gone now) over-priced poor quality stuff in Canada, I remember the no-name-brand trimmer pots. I never tried them.
Instead I bought top quality name-brand (Bourns) trimpots from a real electronic parts distributor (Digikey or Newark) for less cost.
Radio shack gives you instant gratification. Once upon a time, there were many independent neighborhood distributors to choose from, but as fewer and fewer people do things for theirselves, the competitors have disappeared, sadly.
 
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crutschow

Well-Known Member
Most Helpful Member
A typical 1% metal film resistor has a temp coefficient of 100ppm/C or 0.01%/C.
 
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