switching between 2 values

Hi all,

My question is, how can I manage to achieve numbers fluctuating between two values. What I want to achieve is a temperature sensor. I want to set 2 temperature values, say 19-22. So, once the temperature reaches 22, I want the heater turns off and remains off until temperature drops to 19 degrees. After that heater turns on and remains its operation until 22.

I don't have predefined temperature values, so at each step T is calculated where it depends on heat input from the heater.

I have tried a couple if statements but the temperature is fluctuating either around 19 or 22 and tends to stay at one of these values.

Any helping hand will be appreciated, thanks

[Azzi Abdelmalek]

what are products are you using? Matlab? stateflow?

[San]

basic functions of matlab.

Answer 1

[José-Luis]

Maybe a sine wave plus some noise would do the trick?

numSteps = 1000;
temp = 20.5 + 3.*sin([1:numSteps]') + 3*randn(numSteps,1);
plot(temp);

Temperature mean would be 20.5 degrees, the amplitude of the temperature change would be of 3 degrees plus some random change. And if you want the values to fall strictly between 19 and 22:

temp(temp>22) = 22;
temp(temp<19) = 19;

And if you only one 19's and 22's;

temp = rand(numSteps,1);
temp(temp > 0.5) = 22;
temp(temp <= 0.5) = 19;

Cheers!

[San]

Thanks Jose,

But what is important for me is indeed the status of the heater. And using the net heat transfer, I will calculate the temperature for the next step.

[José-Luis]

I misunderstood the question, maybe this is what you meant.

Let's say you are currently warming your system:

isCooling = false;
isWarming = true;

counter = 1;
numSteps =  1000; %or whatever

 while (counter < numSteps)

    while isWarming
        %Calculate T
        counter = counter + 1;
        if counter > numSteps
            break;
        end
        if T > 22
            isWarming = false;
            isCooling = true
        end

    end

    while isCooling
        counter = counter + 1;
        if counter > numSteps
            break;
        end
        %Calculate T
        if T < 19
            isCooling = false;
            isWarming = true;
        end
    end
 end

Using two booleans is probably unnecessary but I left them in for clarity's sake.

[San]

it seems that it doesn't respond to any of the boundaries. It is at off mode all the time. It is weird though.

Could we use for loop instead of the main while loop?

[José-Luis]

I am not sure I understand your question. Maybe the number of steps is insufficient. If you want to go through a certain number of cycles of cooling and warming, you could try:

isCooling = false;
isWarming = true;
counter = 1;
numCycles =  20; %or whatever
 while (counter < numCycles)
    while isWarming
        %Calculate T
        if T >= 22
            counter = counter + 1;
            isWarming = false;
            isCooling = true
        end
    end
    while isCooling
        %Calculate T
        if T =< 19
            counter = counter + 1;
            isCooling = false;
            isWarming = true;
        end
    end
 end

Answer 2

[Azzi Abdelmalek]

 t=1:500;y=20+4*sin(0.05*t)
 action=0
 for k=1:length(t)
    if y(k)<19
        action(k)=1
    elseif y(k)>22
        action(k)=0
    end
 end
 plot(t,y);hold on ; plot(action,'r');grid

[San]

Hi Azzi,

unfortunately temperature is not given. So, if the heater doesn't operate, there is no way that the temperature rises.