[Mini] [minElist] Wiring instruments in parallel or series?

[Richard Porter]

On 19 Mar 2016 John Lieberman jlieberman37 at comcast.net [minilist] 
wrote:

> If you wire any two components in series, they're going to split the
> available voltage.  Plus, if they have unequal current draw, you could
> fry the one with the lower draw because the same amount of current will
> be passing through both components.  Therefore, you would want to wire
> in parallel to keep the voltage constant to every component.

Ammeters generally have low resistance so you can wire them in series. 
Voltmeters have high resistance and can be wired in parallel. That's 
not to say that connecting a second instrument won't affect the 
reading at all. Wiring a voltage sensor across an ammeter doesn't make 
sense. If you wire voltmeters in series you read part of the voltage 
on each meter.

But you need to know what you are measuring. Some traditional car 
instruments are thermal - they are operated by bimetal strips which 
are heated by the current and may have a significant resistance. 
Others can be moving iron or moving coil and usually require a voltage 
stabiliser.

First use a multimeter to see how the voltage you are interested in 
varies over the range of temperature, pressure or whatever you are 
trying to measure. My thinking is that if you've got a high resistance 
sender and a low resistance gauge then the voltage across either isn't 
going to vary that much. If both sender and gauge have a similar 
resistance they will form a potentiometer so you can get a useful 
output from your voltage sensor.

-- 
Richard Porter                        http://www.minijem.plus.com/
Skype: minijem2                       mailto:ricp at minijem.plus.com
I don't want a "user experience" - I just want stuff that works.