Potentiometers

[1951-44U]

Is there any limit to the resistance that a potentiometer wired up to the Analog Breakout can have?

[kamocat]

If you're asking about an upper limit, I would say around 10 kilo-ohms, but you could probably get away with a 50 kilo-ohm pot. Each input has a 1 mega-ohm resistor inline.
If you're asking about a lower limit, that is about 20 ohms if it's the only thing on the analog breakout. The limitation is that the 5v supply on the analog breakout has a 300mA limit.

So, anywhere between 300 ohms and 3,000 ohms is great.

[1951-44U]

Exactly what I wanted. Thank you!

[EricVanWyk]

Originally Posted by 1951-44U

Is there any limit to the resistance that a potentiometer wired up to the Analog Breakout can have?

Not really. Just about anything you can find on the shelf is likely to work. I'd recommend choosing something in the 2k-20k range.

The lower limit is set by how much power can be drawn. Lower resistance draws more power (Power = (5 Volts)^2 / R Ohms). You have about 1W total to play with, which would limit you to 25 Ohms - but that would be kinda silly. Why waste all that power? 1k is good enough lower bound here: 25mW.



As you increase pot resistance, your power consumption goes down but you become more sensitive to other sources of error. The one that will eventually limit you is the input impedence of the NI-9201 - it draws a tiny amount of current to measure the voltage, which can affect the voltage that it is measuring! As a rule of thumb, you want this to be about an order of magnitude of margin. Fortunately, the NI-9201 has a really nice input impedence of 1 mega-ohm. If your pot is less than 100k, you won't even notice it.

EDIT: Gah, beaten by Marshall again!

[Jason Law]

Originally Posted by EricVanWyk

Not really. Just about anything you can find on the shelf is likely to work. I'd recommend choosing something in the 2k-20k range.

The lower limit is set by how much power can be drawn. Lower resistance draws more power (Power = (5 Volts)^2 / R Ohms). You have about 1W total to play with, which would limit you to 25 Ohms - but that would be kinda silly. Why waste all that power? 1k is good enough lower bound here: 25mW.



As you increase pot resistance, your power consumption goes down but you become more sensitive to other sources of error. The one that will eventually limit you is the input impedence of the NI-9201 - it draws a tiny amount of current to measure the voltage, which can affect the voltage that it is measuring! As a rule of thumb, you want this to be about an order of magnitude of margin. Fortunately, the NI-9201 has a really nice input impedence of 1 mega-ohm. If your pot is less than 100k, you won't even notice it.

EDIT: Gah, beaten by Marshall again!

Okay, so is there a particular type/brand of potentiometer that you know is reliable or works the best/well?

We are particularly looking at multi-turn potentiometers. I went to one website and they had over a thousand types of potentiometers.

Thanks,
Jason LaW

[tagayoff]

Originally Posted by Jason Law

Okay, so is there a particular type/brand of potentiometer that you know is reliable or works the best/well?

We are particularly looking at multi-turn potentiometers. I went to one website and they had over a thousand types of potentiometers.

Thanks,
Jason LaW

These are very reliable pots.
http://www.bourns.com/ProductLine.as...pots_multiturn

[Alan Anderson]

Originally Posted by Jason Law

Okay, so is there a particular type/brand of potentiometer that you know is reliable or works the best/well?

All I can advise is this: you get what you pay for.

[Joe Ross]

Originally Posted by Jason Law

Okay, so is there a particular type/brand of potentiometer that you know is reliable or works the best/well?

We are particularly looking at multi-turn potentiometers. I went to one website and they had over a thousand types of potentiometers.

We've used Vishay 534-1-1-502 10 turn potentiometers several times before.