Talk:Potentiometer

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[edit] P vs. transistior

Potentiometers are not used to control high-power devices, such as electric stoves, because of resistive losses, which limit the current-carrying capacity. Typically a pot will be used to regulate a higher power device by controlling the gain of a transistor or other device.

Controlling the transistor's gain by a resistor in order to conserve power is a nosense. AFAIK, the transistors are the variable (transient) resistors. Their resistance is controlled by the base current. Therefore, the techniques like PWM are preferred in the power lines for steppig down the voltage over the Linear Regulators just because of this reason. PWM means a switching mode of transistor (ON/OFF) whereas the linear regulator dissipiates the power resistively. You can adjust the PWM resistively, indeed. --Javalenok 08:45, 9 February 2006 (UTC)

You might use a pot + transistor circuit, though, because the power limit of a pot is usually in the milliwatt range, whilst you can get power transistors that go up to hundreds of watts. As you say, this won't stop the waste of power, but it will work without catching fire. --Heron 19:51, 9 February 2006 (UTC)

[edit] Requested improvements

Remove the invalid redirection "Redirected from Potentiometric analysis" --208.114.161.196 15:50, 18 February 2007 (UTC)

clarify linear movement vs linear taper

A voltage divider commonly used to obtain a smaller voltage.

~~A rheostat is defined as a high power pot and as a two terminal variable resistor in the article. Clarification would be nice as these properties are not associated with each other.~~ (fixed)

Rheostats are constructed differently than pots, and number of terminals the same in both. I have removed the incorrect information and added an external link describing rheostats. A picture of one here would be nice. --ssd 18:45, 8 January 2006 (UTC)

Clarify use of potentiometer as tone control. A resistor(eg pot) on its own has no effect on 'tone' (ie frequency response); it is only when used with a capacitor (or theoretically an inductor), that it can affect the tone of an audio signal.

Sorry if I'm not doing things properly, but this article nagged me. The mention of a rheostat is too brief and seems fairly inaccurate. The rheostat is used to adjust the current in a circuit and these circuits can be low powered (low voltage and low current). Typically, a rheostat is a potentiometer with the wiper tied to one end. They were typically two terminal devices and when they had three, two were shorted. These were very popular at one time and you would have seen them in communication circuits, including stereos. The POWER rheostat was used in larger applications where much power was to be dissipated through the resistor (hence the name "POWER"). There were also applications for reducing voltage using power potentiometers. Some old transformer winding machines had power rheostats to control the motor speed. The rheostat and potentiometer had different schematic symbols too. Remember, in the old days they did not care about conserving energy or saving the environment. Who really cared if a resistor was used to waste power? It did what it had to do and transistors were still fairly new and expensive. So, rheostat has all the mechanics of a potentiometer, except it is a variable resistive load. It does not have to be a resistive wire element, it can be carbon. It can be logarythmic, tapered or linear too! ~DP 12/11/2006

Tell whats the difference between linear, tapered, and logarithmic types. i am a electric engineer, and i sometimes rely on wikipedia to do my electronics!! i consider this piece of article VERY important!! XU-engineer 21:35, 10 June 2007 (UTC)

"(...) a setting of 5 sounds half as loud as a setting of 10", it says in the Audio Control section about logarithmic pots. Shouldn't that be: "5 sounds half as loud as 6?". I don't know a lot of maths. Dafferson 23:10, 3 June 2007 (UTC)

I would like a correction on digital pots. The statement "they allow small adjustments to be made to the circuit by software, instead of a mechanical adjustment." is not correct. It implies that you cannot control a digital pot any other way, when in fact, you can. We use them, but use an electronic interface that has no software or no firmware. It is very simple and some digital pots will allow and up/down switch. The serial ones can be interfaced electronically too and without software or firmware. Not all use I2C bus, many also use a simple two wire serial bus. So, I would suggest this be corrected. Danpeddle 04:38, 4 October 2007 (UTC)

It would be nice to explain Johnson noise and ways manufacturers have designed the resistors to reduce this or at least reference to the fixed resistor, assuming it mentions it. Danpeddle 04:38, 4 October 2007 (UTC)

Can someone add some photos of linear high power potentiometers to show that they are not just circular? (the linear body might be a tube, but they are still linear - see Ohmite) Danpeddle 04:38, 4 October 2007 (UTC)

[edit] Transducer

Calling a potentiometer a transducer is a long stretch. A potentiometer is a variable resistor. A resistor is a passive device and clearly not a transducer. A transducer converts one form of energy into another. At best, a potentiometer can be used as a sensor, but turning it does not generate energy. A pot could be part of a transducer circuit, but all by itself, it doesn't look like a transducer to me. --ssd 04:56, 9 Mar 2005 (UTC)

Agreed - thanks for the input & revision.--Hooperbloob 15:34, 9 Mar 2005 (UTC)

[edit] pot vs. potentiometer

pot is a slang term, and abbreviation for potentiometer, and as such, does not belong in an article like this. Use of the term potentiometer for anything else other than a variable resistor is archaic, and thus it is proper to use the term for this use now. --ssd 20:40, 7 August 2005 (UTC)

Agreed. - Omegatron 21:05, August 7, 2005 (UTC)

Sorry, I think proper potentiometers may still be used in calibration laboratories. Should we have a disambiguation (what a terrible word) page to discrimimnate between the two usages.??Light current 21:11, 7 August 2005 (UTC)

I don't think a disambiguation page is necessary, especially since the derivation of the modern usage is based on the archaic meaning. I think it should be enough to include both meanings in the same article. It really isn't two different meanings, more like a shift in meaning, as the newer device was a part of the older device. --ssd 23:01, 7 August 2005 (UTC)

On re-reading the article, I think it is a bit disorganized. The historical meaning is mentioned in two different places, and the material for rheostat is also a bit scattered through the article. It might be nice if someone (who can write better than me) rearranged it slightly. :) --ssd 23:10, 7 August 2005 (UTC)

I cant agree with ssd that the use of the term in its original sense is archaic. The term means: a 'something that measures potential' and this was its original function. These devices still exist and are used in schools and calibration laboratories. To omit this defn from the 'pedia would be wrong and would damage credibility of Wikipedia. Again I call for a disambiguation page to split the two (differently applied) devices.Could we have more views on this please?Light current 23:52, 7 August 2005 (UTC)

I think the historical meaning used to be in its own section. We can just move it back. That's the best way to handle it, in my opinion. - Omegatron 00:34, August 8, 2005 (UTC)

When you say 'in its own section' do you mean it had its own page?Light current 01:08, 8 August 2005 (UTC)

No, I mean in its own section; under its own heading. - Omegatron 02:40, August 8, 2005 (UTC)

Look here ye disbelievers!

http://physics.kenyon.edu/EarlyApparatus/Electrical_Measurements/Potentiometer/Potentiometer.html http://chem.ch.huji.ac.il/~eugeniik/instruments/test/resistances.htm Light current 04:26, 10 August 2005 (UTC)

I would say you should include the slang. In fact, you already have! There is a photo of trimpots, also written as trim-pots or trim pots. These are slang and short for trimmable potentiometers. These are used to "trim" a circuit such as the feedback of an amplifier or nulling its output to zero volts (or do I say voltage?). Another type of trimpot is the multi turn type, also mentioned. I would say to include "pot," at least to be consistant. But, slang is important in understanding, especially where reference is concerned. And this is used for reference. ~DP 12/11/2006

[edit] New page layout

Ok FIRST we have the intro which has brief defns of both the 'original' potentiometer (the one used for measureing voltages) AND the 'modern' potentiometer.

THEN we have a heading 'Orignal Potentiometer' and do the description of that. Its already there under 'historical'

THEN we do the modern pot under the heading 'Modern Potentiometers' with its different types, applications, method of operation etc.

Now, how does that sound to every one??? Please lets agree on something:-)))Light current 02:49, 8 August 2005 (UTC)

This version was laid out well. - Omegatron 03:02, August 8, 2005 (UTC)

Can we have some more comments apart from O'tron please, please?Light current 03:09, 8 August 2005 (UTC)

[edit] Important!!!Edit Blocking /Interference

I have twice tried to edit this page within 6 hrs and the edits do not go through-the page is the same as the previous version. Is this page locked or only locked for me. Can someone else try and see if they can edit it? Or is there another explanation?? Light current 07:07, 8 August 2005 (UTC)

This page is not as I had attempted to edit it . Please ignore last edit comment saying that this is new layout .Its not- its the old one. Light current 07:12, 8 August 2005 (UTC)

[edit] Relevance of reference to 'VARISTOR'

Why are we keeping the comment on Varistors in here? THis page is complicated enough as it is and a varistor in Nothing to do with pots (not that I ve heard of). Can we remove it please without tantrums & tears??? Comments pleaseLight current 02:19, 9 August 2005 (UTC)

Please leave it. A varistor is not a potentiometer. - Omegatron 04:39, August 9, 2005 (UTC)

What's wrong with a single line mentioning varistor? As for the article being complicated, I don't think it is. Disorganized, perhaps. It's not even a very long article. --ssd 10:49, 9 August 2005 (UTC)

There are many things that are NOT potentiometers, but we do not mention those do we? (thank God). Unfortunately, this is the way articles get confused(by irrelevant additions). If someone wants to mention varistor, it should be in a page on resistors as a special type. Just cos the word may sound remotely similar(both words have a 't' and an 'r' at the end) does not mean that they have to be differentiated here. I vote this entry is moved to resistors. Light current 12:03, 9 August 2005 (UTC)

There are lots of thing that are not variable resistors. I think a term that sounds like a contraction of "variable resistor" will cause a little more confusion than, say, a pie plate. I think it is more useful than not, and can't believe we're spending these many electrons talking about a single, short, insignificant sentence. It was probably added by someone who was confused by the issue, and I'm sure there are others out there.

Yes, the article is disorganized now. Deleting a single, relevant sentence won't help that at all.

And no, it's not long at all. - Omegatron 12:59, August 9, 2005 (UTC)

Just following your example, O. Anyway we are not wasting electrons. See the page on capacitor operation. I never said it was long but it will be when I have added all the omissions! Light current 13:10, 9 August 2005 (UTC)

From your last comment ,O, it seems that you may be thinking that a 'varistor' has something to do with 'variable resistor'. It is NOT a user variable resistor (like a pot). It is in fact a voltage variable resistor and usually operates on semiconductor principles giving a non linear resistance against applied voltage. It is not a very good name for the device, I admit, but we are stuck with that. It is therfore completely out of place on the Potentiometer page. Lets move it to the resistor page where it would fit better(not perfectly, but better). I once again refer you to Uncle Albert's maxim :-) Light current 13:27, 9 August 2005 (UTC)

WE KNOW THAT. THAT'S WHY THIS SENTENCE IS ON THE PAGE.

iT SAYS... *ahem* ... It says "although the term "varistor" sounds like it might refer to a variable resistor, varistors are not the same thing". It's a helpful statement for people who might be confused, as you have just admitted is a common misunderstanding. Why would you want to delete that? Did you actually read the sentence before deleting it?? - Omegatron 15:25, August 9, 2005 (UTC)

Keep calm., O. You know its not good for your blood pressure to get too excited!!(HAL: Take stress pill Dave..). In this case, since the term 'varistor' has a link ,appears in braces, etc I am happy(ish) to let it remain. BTW I didnt say it was a 'common misunderstanding' , I just sain that you appeared to be confused by the term.:-) Light current 17:38, 9 August 2005 (UTC)

I AM CALM!!!!1!!!

:-) Honestly, I am getting somewhat stressed since you arrived. I understand your motives and you have a lot of good knowledge to contribute, but we obviously clash on what's appropriate info to include, and I feel like I have to closely follow all your edits to make sure you're not breaking anything. (And your enthusiasm and spending lots of time on here is great, and I'm glad you're contributing so much, but now I'm spending a lot more time on here than I normally would trying to keep up.) :-)

No, I know about varistors. I was explaining to you that it's a common misunderstanding so this "unconfusing" statement belongs in the article. Please read my comments again and you'll understand. - Omegatron 17:51, August 9, 2005 (UTC)

Seems to be some gobbbledegook left in final para . I dont know what it means. Does any one have an input B4 I attempt to make it make sense?Light current 18:45, 11 August 2005 (UTC)

Yeah, that section needs work. I'm going to draw a schematic for it. - Omegatron 21:53, August 11, 2005 (UTC)

Yes I think your description of theory is more than adequate. Nice job! :)Light current 00:55, 12 August 2005 (UTC)

[edit] Taper markings

So confusing. The article currently says one thing while this link says another, and I can't find any other info anywhere. — Omegatron 20:53, 19 January 2006 (UTC)

I've always hated the mention of these markings anyway. The article does not even make it clear that this is a standard of some sort, it just introuduces the marking without saying why. Now you find a page that essentially says the markings are useless. Granted, I don't buy pots every day, but I've never (before now) even heard of this, and I've never used it when looking for a potentiometer. Given the existance of conflicting markings, I'd be tempted to remove any mention of them. --ssd 12:47, 24 January 2006 (UTC)

No way. We need to include information about all of them. — Omegatron 14:36, 24 January 2006 (UTC)

Vishay application note on potentiometers also [1] (PDF)
Rane Pro Audio Reference definition of potentiometer
Bourn's notes on taper and linearity (PDF)

In my Electronic Engineers Handbook 1975 ed (Fink) it says

type A is a linear pot (the term taper is used but the element is not tapered)
type B is a tapered pot with a CW taper(log?)
type C is a tapered pot with a CCW taper (antilog)

Is this any help? In the Bournes link they swop the A and B so that the A type is CW log. I assume this is because A alos stands for audio. Now which convention shall we use?

--Light current 15:46, 21 February 2006 (UTC)

Well, it's 2006; not 1975. The link above says that there are different codes for now than there were in the past. Assuming you got the CW → log/CCW → antilog right, yours is even different from the "old" system mentioned:

Taper	Old Code	New Code	Alternate
Linear	A	B	LIN
Log (Audio)	C	A	LOG
Antilog	F	N/A	N/A

Who do we believe? — Omegatron 19:20, 21 February 2006 (UTC)

I would tend to go with the pot manufacturers although Bourns and Vishay differ. I would plump for Bourns and say other manfs may have different designations.--Light current 22:21, 21 February 2006 (UTC)

More construction of the pots should be mentioned, laying more attention to the resistive element. Some have steps that are very apparent and others have a coating that seems to have a more continuously variable resistance. DP 12/11/2006 —The preceding unsigned comment was added by Danpeddle (talk • contribs) 02:21, 12 December 2006 (UTC).

[edit] Logarithmic pots

What sort of physical taper would you use on the resistive element to get a logarithmic variation of output voltage with shaft angle (assuming constant input voltage) ?--Light current 16:08, 21 February 2006 (UTC)

A logarithmic taper. :-) — Omegatron 19:37, 21 February 2006 (UTC)

Dont think so! If o/p voltage varies with (position)^2 as it would with a linearly tapering track, you would get a non linear relatinship between o/p and shaft angle. That is: O/P is propl to (x.y) where both and x and y depend on shaft angle. Get it? So how would you get a log o/p?--Light current 22:17, 21 February 2006 (UTC)

Well, I guess it depends on your definition of "logarithmic", but yes, the taper (resistivity or cross section) would vary in a logarithmic way. Logarithms beget logarithms:

If we think of the pot as two resistors:

and call the position of the pot x (varies from 0 to L), the output voltage is directly proportional to R2, since

R total

and Vin are fixed. I'm going to rename R2 as R(x).

If we have a linear pot,

$R(x) = {x \over L} R_\mathrm{total}$

R(x) is the resistance from the wiper to the ground connection, and if the resistive element is a constant resistivity and cross section, the resistance is:

$R(x) = {\rho \over h} \cdot {x \over w(x)}$

The width function w(x) is just a constant, so $R(x) \propto x$

now say we want to get a logarithmic pot, with a resistance vs position function like

$R(x) = {e^x - 1 \over e - 1} R_\mathrm{total}$

, which looks like Bourns red line #2. We want to find the width function w(x) that matches this (but the function :needs to be an integral since w(x) changes):

$R(x) = {\rho \over h} \int_0^x {1 \over w(x)}\,dx$

${e^x - 1 \over e - 1} R_\mathrm{total} = {\rho \over h} \int_0^x {1 \over w(x)}\,dx$

$\int_0^x {e^x \over e - 1}\,dx = {e^x - 1 \over e - 1}$

so we need width vs position $w(x) = {e - 1 \over e^x}$ .

This is a pretty sloppy description, but in my book that counts as a logarithmically varying width/taper. — Omegatron 03:07, 22 February 2006 (UTC)

Or, to put it another way, since o/p voltage is a linear function of your R2, then R2 must vary logarithmically with shaft angle to get a logarithmic variation of output voltage.

So this implies that a linear function multplied by a log function is a log function (correct I think). But if the pot had a proper linear taper of X sect, we would get, at the output, a voltage that was a function of the square of shaft angle (or displacement along the resistive track). Interesting!--Light current 06:03, 22 February 2006 (UTC)

[edit] ON/OFF Switches in pots

Do we really need to mention these switches as thay have nothing to do with the operation of the pot as such?--Light current 22:05, 4 March 2006 (UTC)

Yes. — Omegatron 18:53, 1 August 2006 (UTC)

I disagree! 8-) I will remove refs to such ASAP--Light current 21:08, 1 August 2006 (UTC)

Looks as tho' we are arguing over nothing 8-)). I can see no ref to switches on this page. BTW 'O' on a personal note, how are you keeping? --Light current 22:21, 1 August 2006 (UTC)

How strange. It's almost as if someone removed it without any consensus whatsoever on the talk page. Now when people search for information on pots with switches, they won't find anything, and Wikipedia will fail in providing comprehensive coverage yet again. Pretty irritating, huh? When people spend time and effort adding information to the encyclopedia and then other people delete it for no good reason? I hate when people do that. Some people just won't accept that wiki is not paper. — Omegatron 13:52, 2 August 2006 (UTC)

Well to be quite fair 'O', my notice (above) stood unreplied to 5 months. It looked like no one was bothered! 8-|--Light current 15:19, 2 August 2006 (UTC)

I have re inserted a ref to pots being available with switches although this was already mentioned in the context of 'on-off' switches being combined with vol controls in consumer equipmnet. Happy?--Light current 15:44, 2 August 2006 (UTC)

Did you revert to an old version by accident? I don't understand why you made so many changes. — Omegatron 16:53, 2 August 2006 (UTC)

Quite possibly. Im feeling a bit groggy today. ill investigate --Light current 17:48, 2 August 2006 (UTC)

Looks like I did revert to an older version. Apologies! This should now be the correct version with the switches mentioned--Light current 17:58, 2 August 2006 (UTC)

[edit] Schematic symbol

Wasn't the zigzag replaced aith a box about two decades ago? Just zis Guy you know? 22:10, 12 April 2006 (UTC)

Dunno what official standards say but in my experiance both zigzag and box symbols are still frequently seen in practice. Plugwash 13:15, 22 June 2006 (UTC)

They're both used quite commonly. I think the box is more European and the zigzag is more American, but both use both. — Omegatron 14:38, 22 June 2006 (UTC)

Use both symbols. As mentioned above European and American symbols differ. This is very common. Also, marking of components vary greatly too. For schematic symbols, Europe has their standards and Americas have theirs. There typically are not standards for component markings. A good example is the common LED. Most people will tell you the flat side represents the cathode, but it does not. The specification sheet is what you must read to find out where the cathode is or you can attempt to apply a low constant current (2mA, some pcb indicator LEDs will be damaged with greater currents) to the ends. If you don't believe me, look up LEDs from some manufacturers (Fairchild, SunLED, Chicago Miniature, etc...). Capacitors and inductors are worse. ~DP 12/11/2006 —The preceding unsigned comment was added by Danpeddle (talk • contribs) 02:30, 12 December 2006 (UTC).

I don't believe you. :-) Can you provide examples of two-pin LEDs that have flat sides with opposite meaning? — Omegatron 14:59, 12 December 2006 (UTC)

The cylindrical LED does not need a flat spot on the plastic package and does not need a shorter lead to denote an anode or cathode. Here is one LED component that has the anode on the flat side and the short lead on the cathode... http://www.mouser.com/catalog/specsheets/XC-600110.pdf And, if needed, I will find more of these from other manufacturers (you can see some paging through distributor catalogs like I did). But, right now I have too many project deadlines to complete before the end of the year. The manufacturers do not make this visible on their website, you need to download the datasheets often to find out. Here is a web page that discusses this issue and uses it to make an LED tester, but, it's current can damage the 2mA LEDs that are out there. http://www.web-ee.com/Electronic-Projects/projects/led_test/index.shtml A simple method is to use something like an LM317 in CC operation or the LM234, set the current for 2mA (or make it adjustable to ~20mA - Note luxeon type LEDs will probably not emit) and clamp the max voltage to about 3.3V with a zener. Oh, and that LM317 CC circuit would use a variable resistor known today as a trimpot, but set up as a rheostat. Anyway... a tangent... Even the IR LEDs may use the flat spot for the anode. This also holds true for the topmount LEDS, except it is the location of the dome instead of a flat spot. If you ever designed with LEDs, you would have come across this several times. It is also written in hobby books and text books. What most people believe in is a rule of thumb, not an industry standard. Never trust a rule (ruin) of thumb, they can be horribly wrong. If you want an example of a rule of thumb fiasco, ask, I have a good one from a company I worked at. BTW... A good power indicator is to use an LED in series with a zener very near the max voltage (with current limiting resistor for safety). It will turn on close to the max voltage (remember, LEDs and diodes are "leaky" valves and zeners have a knee). Sorry about the info overload and I'm not editing this. I hope this helps you understand more. If not, let me know. P.S. You made me curious about the LED info on this site... Ummm... I do not have the time to comment completely, but, there are some things that are not correct. ~DP 12/12/2006

Omegatron do you believe me now or do you require more proof? There are also LEDs in the same cylindrical package, but without a flat. Instead they use the lead length to determine the polarity. Danpeddle 18:52, 15 December 2006 (UTC)

[edit] Page split

Split into modern pots and old fashioned potentiometers (measuring instruments) ? 8-|--Light current 02:09, 11 June 2006 (UTC)

Why?
Didn't we already have this discussion? — Omegatron 04:44, 11 June 2006 (UTC)

Because they are actually different things doing different jobs, but with the same name.
Yes. But its more urgent now

--Light current 22:01, 21 June 2006 (UTC)

Is no one bothered about splitting the page just yet? Ill go with the consensus.--Light current 12:48, 26 June 2006 (UTC)

[edit] Resistive element

I accessed article for description of types of element ie carbon, conductive plastic etc and include pros and cons. This article would benefit from including such information. Richard 02:22, 30 June 2006 (UTC)

Agreed. — Omegatron 23:11, 4 August 2006 (UTC)

[edit] "Constant current potentiometer" Needs Diagram

I came here (as a reader) from Weatstone Bridge looking for a comparison between the wheatstone bridge as described in Wikipedia and the original use of the potentiometer. The present article describes the measuring use of the potentiometer via a series of variants, the first of which is the "Constant current". Understanding all of them depends on understanding the first. In "Constant current", there is verbiage that appears intended to describe the circuit, but a diagram would make it clear. Jack Waugh 17:58, 21 September 2006 (UTC)

[edit] potentiometer= v divider!

the basic operation is that of voltage dividing.

rheostats were used at the beginning of electricity 1890s -- transistors were starting to be used in the mid1950s, after manufacturers learned how to make them with consistent characteristics.

the picture of the rheostat shows part of a toroid, over an insulated core -- —The preceding unsigned comment was added by Cem BSEE (talk • contribs) 14:41, 29 December 2006 (UTC).

[edit] String pots and resistance wire

These [2] are examples of what I call a "string pot". This device consists of a linear multi-turn potentionmeter attached to a spring-loaded spool of stainless-steel wire. As you unreel the wire, the spring loaded spool turns the potentiometer which results in a varying output voltage. There is no electrical connection to the wire. It is misleading to call the wire "resistance wire" as the resistance of the wire is uncontrolled and there is no reason why a string pot couldn't be make with a non-conductive material instead of stainless-steel wire. If I should leave "resistance wire" in the article, please comment here or on User talk: Sagsaw Sagsaw 17:47, 29 December 2006 (UTC)

Sorry I think you got it wrong! String pots do use resistance wire. See some of the links in the article.--Light current 02:02, 5 January 2007 (UTC)

That's entirely possible. I took a quick look at the links that looked relevant, but I couldn't find an example of a string pot in which the spooled wire/string is part of the circuit. Please let me know which links you're talking about. Sagsaw 03:45, 24 January 2007 (UTC)

I may be wrong. Im thinking of the term slidewire not string.--Light current 17:35, 24 January 2007 (UTC)

[edit] Rheostat/Rheotomes

The reference to an early Edison patent for a carbon potentiometer in 1872 needs work. Historical web sites such as www.tomedison.org/invent.html refer to Edison's 1872 invention of the "carbon rheostat" which consisted of powdered graphite in glass tubes that changed resistance by increasing and decreasing pressure on the graphite with a screw/knob. Edison abandoned this because it was too sensitive to vibration. I could not find his patent for this. Edison got a US patent 131,334 titled "Rheotomes or Circuit-Directors" but this is for a selector switch, not a rheostat, although a simple modification could change the switch into a multi-tap potentiometer as was used in radio broadcasting studios and audio recording studios where they were called "pots". In 1877, Edison revived the vibration-sensitive rheostat for use as a carbon (graphite) telephone transmitter. On the web site edison.rutgers.edu/sernote3.htm near the bottom there is a reference to Edison's notebook entry for a "carbon rheostat" in 1873. Rheostats using a screw/knob to vary current by varying pressure on graphite were used in power supplies for vacuum tube radios during the 1920's and 1930's and they were labeled rheostats. Greensburger 02:10, 5 January 2007 (UTC)

[edit] Rheostat vs. Potentiometers

It seems their is too little understanding of what is a rheostat. You have stated a rheostat "is usually much larger, designed to handle much higher voltage and current" when comparing to a potentiometer. Please, understand what you are writing so the wiki world doesn't look so foolish! This is a statement that an uneducated novice would make.

A rheostat is a two terminal variable resistor used to control current. It has one fixed end and one variable end (the wiper). They can be high power high voltage, low power low voltage or anything in between. They can also be linear in shape or any shape a potentiometer comes in. They can be linear taper, log taper, any other taper and even digital.

A Potentiometer is a three terminal variable resistor used to control voltage (variable voltage divider). It has two fixed ends with a variable middle (the wiper). They can be high power high voltage, low power low voltage or anything in between. They can also be linear in shape or any shape a potentiometer comes in. They can be linear taper, log taper, any other taper and even digital.

Basically, they are the same component, except the rheostat has either a wiper shorted to one fixed end or the second fixed end of a potentiometer is not connected to anything. Try it, take any potentiometer and short the wiper to one fixed end and you have a rheostat or do not connect the second fixed end in your circuit! Please note, that it is better practice to short the wiper to one fixed end of a potentiometer or purchase a rheostat.

BOTH a potentiometer and a rheostat can be seen as varying the resistance (depending on where the measurement is made). After all, they are VARIABLE resistors.

They are also represented slightly different schematically. And, speaking of schematic symbols, the rheostat actually has two; one that shows it's wiper connected to one end and one that shows an arrow THROUGH a resistor (no connection of the arrow to the fixed end)

Danpeddle 04:09, 4 October 2007 (UTC)

OK, sounds good. You sound well qualified to update the article to make the distinction then. --Hooperbloob 22:04, 28 October 2007 (UTC)

A rheostat is definitely a two-terminal device - the essence of the "potentiometer" is the variable voltage divider, three-terminal configuation. --Wtshymanski (talk) 16:11, 17 December 2007 (UTC)

[edit] Digital pot section

I've removed the following text from the digital pot section, because there really isn't any tie in to this article. A digital pot could be used to create a hybrid digital and analog control system, but nothing in the removed text really describes how a digital pot would be used in such a system or the advantages/disadvantages of using a digital pot in such a system. Sagsaw 18:20, 28 October 2007 (UTC)

For the most part, the universe of feedback system design separates neatly into two fundamental design paradigms: analog-based designs and digital-based designs. Both design strategies are characterized by advantages and liabilities that generally make one or the other a clearly superior choice for any given application. Pure analog designs, for example, tend to display design simplicity and low development costs that play well in the context of smaller system applications. Digital-based designs, by contrast, have essentially unlimited flexibility in computation of the feedback function and therefore dominate in more complex feedback applications in which higher development costs (generally including software implementation) can be justified. Sometimes, a feature of particular utility in digital designs is the availability of digital memory with its ability to store feedback parameters for arbitrary lengths of time without drift. This makes possible a variety of system solutions including multiple system operating modes in which feedback values can be acquired in some modes and then applied in others

[edit] Common vs rare

There is currently no evident distinction of common vs rare uses. Use of the pot as a voltage measuring device is surely the latter today, being more relevant to early history and standards work rather than common electronic use.

Also the fact that this was its first use explains the ending 'meter' for what is today an item that has more or less nothing to do with metering. This could be spelled out. Tabby (talk) 06:47, 3 January 2008 (UTC)