Comparing two input voltages?

I'm attempting to build a ride by wire system, I've built a proof of concept in Simulink utilising an Arduino as the controller.

Now I've moved on to real hardware with a RBW throttle, it uses two hall effect sensors to give two voltages. On one it gives a range of 0.9 - 4.4v and the other is 0.4 - 2.2v. I've looked through various blocks but I'm struggling to see a way forward and would appreciate any guidance on this problem.

[Adam Danz]

Sounds fun! What's your question? What do you mean by 'comparing the voltages' ?

[Philip Harris]

As you turn the throttle the two signal voltages increase, one signal should be approx half the other. It's part of a safety measure to ensure you get a correct throttle input but I'm currently unsure how to implement this relationship.

[Adam Danz]

You are uncertain how to implement it physically using resistors or the arduino or you are unsure how to implement code that scales one signal to be half the value of another signal? Sorry, I'm still catching up with you here.

[Philip Harris]

Implementing the code.

It's almost like a verification. On other throttles the relationship is 0 - 5v and 5 - 0v as you require one signal to verify the other otherwise if it falls out of sync you need to flag an error code as riding the vehicle would become dangerous.

So on mine if signal 1 is 3v then signal 2 should be ~1.5v before then passing signal 1 forwards to operate a servo.

[Adam Danz]

I continued in the answers section now that we're getting closer to understanding the problem. If I'm still off base, I can remove that answer and we can continue here.

Answer 1

[Adam Danz]

"if signal 1 is 3v then signal 2 should be ~1.5v before then passing signal 1 forwards to operate a servo."

If signal 1 is an instantaneous value s1 and signal 2 is an instantaneous value s2, would this work?

s1 = 3.012;       %3v + some noise
s2 = 1.490;       %1.5v + some noise
tol = 0.05;       %Noise tolerance; so s1/s2 must be +/- tol from 2

if abs((s1/s2) - 2) > tol          %Test that s2 is 1/2 of s1 within tolerance
    %[enter code to stop servo]    %system fail
else
    %[pass signal to servo]        %your system is working
end

The conditional statements would be wrapped in a while-loop or whatever controls your system and receives s1 and s2.

[Philip Harris]

That looks like a plausible solution, thank you. Is there a specific block in which you can input this within Simulink?

Unfortunately I've only used the software recently and it's not well supported at my University.

[Adam Danz]

I'd put it in whatever block recives the s1 and s2 signals so your system can react to a discrepency right away.