Re: ---My wiring questions (was progress on Travelette - premature sending)

["Allan Ericson" <lowvolt@xxxxxxxxxxxx>]

If you set the meter on the 20 volt DC scale, you put the leads across the
light bulb, you get a reading. There are two terminals on the light bulb.
"Across" means the meter is in parallel with the load.

Likewise, on the rheostat, there are two leads in series with the light
bulb. You put your meter across them. The two voltages (across the bulb and
across the rheostat) add up to the total voltage in the circuit, less any
losses for wire lengths or anything else you may have added into the
circuit. The impedance of the meter is so high that it will not
significantly affect the readings.

[trivia mode]
In a circuit where the current can be measured in microamps, you also must
figure the parallel impedance of the meter when you make the measurements.
This is especially true of analog meters. That's another subject, though.
[/trivia mode]

A potentiometer (variable resistor) has three leads. Two of the leads are
the total resistance of the unit. The third lead is the "wiper" and the
value of resistance changes as the potentiometer is turned. From one end it
increases, and from the other end, it decreases, depending on which way it's
turned.

If you tie the wiper to one of the leads, it's called a rheostat. In either
case, the load is always tied to the wiper, whether you hook it up to "tap"
the circuit or as a rheostat. You would measure from the side "opposite" the
load, since the rheostat will work on either side of the bulb.


----- Original Message ----- 
From: "John Hofstetter" <hofs@domain.elided>
To: "Allan Ericson" <lowvolt@domain.elided>
Cc: "T.R.E. Jr." <T_R_E_Jr@domain.elided>; "IHC Digest"
<IHC-Digest@domain.elided>
Sent: Sunday, June 29, 2003 12:57 PM
Subject: Re: ---My wiring questions (was progress on Travelette - premature
sending)


> On Sunday, June 29, 2003, at 12:40  PM, Allan Ericson wrote:
>
> > Measure the voltage across the rheostat when you have the light
> > exactly how
> > you want it.
> >
> Allan,
>
> What do you mean exactly when you say measure the voltage across the
> rheostat?
>
> Interested observer