5

Is there a special name for a potentiometer whose A-W or B-W resistance can drop to zero? I have a 1k +/-10% pot and I can only vary A-W or B-W resistance from 118 ohms to 1.2k. Note A, B refer to the outer pins and W the wiper pin.

Thomas O
  • 31,786
  • 58
  • 184
  • 322

5 Answers5

8

I suspect that what you're seeing is a combination of a poorly-manufactured pot and the resistance of the connections to the pot. There's always a couple ohms of resistance in anything you measure, just because you can't attach your multimeter to anything with infinitely low resistance wires. But beyond that, you just have a lousy pot.

pingswept
  • 12,651
  • 4
  • 46
  • 66
  • 1
    Zero reading on meter is 1.1 ohms, it's a cheap meter. But it checks out against some 330 ohm +/-1% resistors, reading 331 ohms. The pot is made by "ALPHA" and has a small encircled "a" stamped on it. They only cost about 25p each though, so you're right, they are cheap. – Thomas O Nov 09 '10 at 14:07
4

Do you mean "silvered ends"?

Top Silver End Terminations (CP Only)

A type of tap used for excitation, wherein the connection is placed on the conductive film. This is the most common connection which is used, and has an end resistance below 0.5Q. For certain applications requiring a smooth transition from end to function, this tap may not be suitable. See Fig. 1A.

Precision Potentiometer Tutorial

End resistance on pots is pretty normal. Audio controls at their minimum often still bleed through a little, like -60 dB.

Community
  • 1
endolith
  • 28,734
  • 24
  • 119
  • 184
1

You could easily have one made where the wiper goes onto a straight conductive surface at the ends, but I don't know what they're called.

For low-volume/prototype, you might be able to use a rotary switch with a pot (some seem to stack) to accomplish the same thing by using the switch to short the wiper at the tail end. May be similar to volume/power knobs.

Nick T
  • 12,480
  • 2
  • 45
  • 72
1

Can "potentiometer with switch" be the name ? You need just wire the switch to A and W. So it will guarantee a very good zero (when turned counter clock wise all way until click).

  • This is what I was going to suggest. Plenty of cheapo pos available with switch. – ttt Nov 12 '10 at 13:33
0

The way to achieve what you are asking is probably either really expensive or impossible.

A good engineering practice is to design a circuit allowing for 10% tolerances, anyway.

J. Polfer
  • 3,790
  • 2
  • 28
  • 33
  • The pot may be +/-10% but the offset is 150 ohms (typ.), this is across multiple potentiometers. – Thomas O Nov 09 '10 at 13:57
  • The question did not said anything about price. Also some specific equipment are tailored to be as best as possible, ex: astronomical instrumentation. Some cases 10% tolerances are not acceptable. – RMAAlmeida Nov 10 '10 at 17:18