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Here's what I working with. I'm researching some three terminal potentiometers for use as adjustable voltage dividers. The outer terminals are connected to 0V and 5V respectably, so as I turn the knob, the wiper voltage sweeps from 0 to 5V.

My question: Does the tolerance of the potentiometer (5%, 10%, etc.), or the resistance matter for this application.

I'm not sure about the tolerance, but I'm pretty certain that the resistance will only affect the size of the load that the wiper can drive (impedance and what-not).

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If you are just taking the voltage into a high-impedance load, then the value of the pot doesn't matter at all. 1k and 10k pots will both give 2.5V at 50% rotation.

It is a common pattern in electronics to make things ratiometric so exact values don't matter. In this case, the tolerance and temperature coefficient of the pot is completely canceled.

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    \$\begingroup\$ temperature coefficient could still be relevant if there is a (time variable) temperature gradient across your potentiometer (e.g. if one side is close to a power resistor/transistor and the other side is close to the frame) \$\endgroup\$ – Curd Jan 15 '12 at 19:28
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The tolerance is a plus/minus percent rating of the total resistance. I.E. A 100 Ohm pot with a rating of 10% could actually be a 90 Ohm pot or a 110 Ohm pot. As you are using a pot to give your voltage divider fine tuning ability, you won't need to care if you are a little short/long on the top end. Figure out what your current needs are and pick your pot based on that.

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The tolerance of your divider will be driven by how accurately you adjust the potentiometer (by hand). Without knowing anything else, 10% tolerance in the total resistance of the potentiometer shouldn't make difference.

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Some pots have a tolerance value for overall resistance, as well as tolerance values for angular/ratiometric accuracy. If you want your pot to translate angles into resistance ratios, you don't need to worry about the first spec at all, but the second may be very important. Many pots are used in situations where such accuracy is not really important because a human being will simply turn the knob until a desired brightness, sound level, or other adjustment is achieved. On the other hand, if you are using your pot for positional feedback in a situation where accurate absolute positioning is required, a pot where a ten-degree rotation in one area will affect the pot's ratio by 3 percentage points but a similar rotation in another will affect it by 5 percentage points, could yield inaccurate positioning behavior.

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You did not ask, so I hope you know that the load on a voltage divider is very important. If you do not understand it, then work on getting informed.

The important spec. I think you need is the taper of the pot. You probably want a linear taper and these are usually specified as a percentage. 10 turn pots are more finely adjustable, bu may not be more linear.

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  • \$\begingroup\$ Thanks for the response. The only "load" is the ADC input to my microcontroller. That's why I didn't bring it up. \$\endgroup\$ – Chris Laplante Jan 15 '12 at 19:46

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