Off The Beaten Path

What is the difference between a potentiometer and a rheostat? Is a volume control knob an example of a potentiometer?

Take a look here .

Commonly, the potentiometer is used in the field of electronic, it is a gain control device. When I say gain, I mean that it usually will be used to cotrol a variation in voltage. Since Voltage does nothing, it controls a potential. An potential is nothing, tinck of Mike Tyson.

Commonly, a rheostat does real work. We can see rheostats on welding machines. A rheostat will control current. Current does a lot.

We see BIG rheostats and SMALL potentiometers.

I have never seen a potentiometer weighting 10 pounds. A rheostat yes.

I hunderstand that this answer is simplistic but so is the question.

technically a variac is a potientiometer

AND many of them are quite large and weigh 10 lbs

A potentiometer is used to control voltage..therefore is a 3 wire device. + DC is connected to a terminal (not center/wiper) and -DC voltage to another (not center/wiper) and center/wiper is the difference of the 2 inputs as the dial is turned...ie a 1000 ohm 1 turn potentiometer when turned halfway will have 500 ohms resistance on the center connection...if voltage applied is 10vdc then the reading would be 5vdc, 100 ohms = 1vdc, 1k ohms= 10vdc.

Potentiometers are in most cases small and low wattage devices, but there are larger high wattage devices available when needed

Rheostats, which are potentiometers that only use 2 of 3 connections to control current are available in many sizes, shapes and configurations, these are normally DC devices.

I mentioned the VARIAC because of a recent post, the name should show its an AC device, works similar to a potentiometer thougn.

SOO.... In a sense both pots and rheos are types of resistors?

Thats exactly what they are, variable resistors, the application and/or connections determines whether they control voltage or current.

Think of a circuit with a variable resistor in series with a load, vary the resistance and you vary the current to the load...thats a rheostat.

Think of a circuit with a variable resistor connected in parallel on a line..2 wires connect to the line voltage and 3rd is a variable voltage with a reference from either + or -.

Look at any potentiometer and it will be rated for an OHM value...an ohmmeter can check the values across it or from either end to center, center will vary over the scale.

Same goes for a rheostat, it has an ohmic rating and can be measured.

Thanks

Let us know how your exam goes

No, I'm not a student. I'm working full-time but trying to learn electronics. THANKS

Just another bit of info concerning pots and rheostats. We know the rheostat is essentialy a 2 wire device that controls current..any 3 connector pot can be made into a rheostat...just short the center wiper with another connector...note you have to pay attention to which one because of the KNOB..ie the direction it turns. When you turn sound up (as your first example) its normally clockwise, counter-clockwise is down...the application may determine whether resistance is high or low per direction.

The other aspect of resistors is that they can be used as voltage dividers...naturally a pot is a variable voltage divider.

Steve Bailey ...

I looked at your site reference and found one of my favorite information sources. This guy, Glen Williamson has set up a great site for learning electronics. He'll even respond to questions. Quickly, too.

For those that aren't aware of what we've refered to, check out:

www.williamson-labs.com

Warning, he also is politically opinionated and patriotic. Shares his opinions front and center. Regardless of what your own political philosophy might be, revel in it, ignore it, but check out the tutorials on just about everything electronic or electric.

Won't have anything on PLCs though. Phil has created an incredible venue for all that kind of info, right here.

... rab

GREAT LINK

The electronics ref is nice, very nice, BUT the rest of the site is GREAT. Thanks for the link Bob