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[DPRG] Current Sensing -- How to Do It?

Subject: [DPRG] Current Sensing -- How to Do It?
From: DeltaGraph at aol.com DeltaGraph at aol.com
Date: Mon Jul 19 08:43:10 CDT 2010

Overhead video camera sounds like least number of wires?
Hall effect sensor would "see" the car with no added magnet -- me thinks,  
but does sound expensive.
Modern current detecting ICs (at least inline versions and not  inductive), 
as far as I know, are amplifiers capable of amplifying very tiny  voltage 
drops. Would be interesting to see cleverest way to do this sensing --  each 
track rail forming a complete loop around the track, each track segment  
reporting a slightly different voltage as the car moves around the track.
I am thinking you could do differential drop voltage analysis on say a  
total of three points on the track to get your solution. That is, if you  
measured voltage at location where you are supplying the track and two other  
points say about 1/3 distance around track. you should  be able to get your  
solution. Two sensors almost works, but you won't have a unique solution.
You might want to draw each track conductor as a series of resistors  
arranged in a loop. Maybe for fun 4 resistors at 1 ohm a piece. Then maybe make  
the car 1 ohms for the sake of simplicity -- see what happens as you put the 
car  in different positions and solve the network. Put the voltage supply 
say 10  volts at one corner, and look at what happens as you put the car 
resistor  across each set of corner nodes. When the car is at the position of 
the source,  all sensors read 10 volts. Of course in real life each track 
segment is a  distributed resistance with. 
Anyway, I think this technique would allow you to solve for load being  
generated by car, if I got it right.
The voltage differential measurement would be among points on one of the  
If resistances are not that predictable for real-world track, maybe you  
would have to experimentally test/train the system?
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