Trying to plot a simple linear function but returns constant

Hi! I'm working on a temperature sensor and I've found its equations on this link: PT-100. It's a device which electric resistance depends on temperature changes and it can be easily measure with a voltage output when it's apply on a bridge circuit.

But in general the code is the next:

clear all
close all
clc

T = 0: 0.01 : 200; 

alpha = 0.00385; 
R0 = 100; 

RT = R0 * (1 + (alpha * T));  % ............(1)

V_cd = 5;

Voltage = ((RT/(RT + R0)) - 0.5)*5; % ..........(2)
subplot(2,1,1)
plot(T,RT)
ylabel('Resistance');
xlabel('Temperature °C');
grid on;

subplot(2,1,2)
plot(T,Voltage);
ylabel('Voltage');
xlabel('Temperature °C');
grid on;

(1) and (2) are the functions that I'm trying to plot, RT (1) is a function that depends on temperature changes T = 0:0.01:200 -> °C, and Voltage depends on RT output. When I plot RT vs T it returns a linear function on a graph, but when I plot Voltage vs T it returns a constant!!

I think I'm doing something stupid but I can't find the problem hahahah I always use matlab for modeling electronics but it's the first time I got a plotting problem with matlab :(

Answer 1

[the cyclist]

You were accidentally doing a matrix division, instead of element-wise division. Try this instead:

Voltage = ((RT./(RT + R0)) - 0.5)*5; % ..........(2)

Notice the "./" in place of just "/".

[Esteban Torres Pérez]

wow! It's solved! thanks a lot cyclist! Now I'm interested on this "./" what is it? I'll search about it! seriously thanks :)

[the cyclist]

An important thing to remember is that MATLAB has a strong emphasis on matrix operations, from its original on linear algebra. So "*" and "/" are matrix operators, which can surprise new users.

Here is one documentation page that discusses array vs matrix operations.