Temperature control by a heating ramp

Dear all

I buy today all components to do my project.

-arduino
-lcd and i2c
-5v relay
-lm35 temperature sensor

I would like to make a controler from a test equipement that consists a heater plate and a cup of water.
I need to heat the water a a rate of 5c/minute from ambient temp until 100c.

I tryed in other program language (labview), but in arduino code I think I will find problems how to configure the code for the ramp. And my loop must be shorter to be more precise.
Another thing is that the heater plate at the begin is not fast, so the "ramp" must wait (=0) when we have incresing temperature the ramp can control the relay for tunr on/off the plate.

Hoppe you understand the project and help me to developt this part of the ramp.

Best regards

cpalha

And my loop must be shorter to be more precise.

Shorter than what? To be more precise than what? If you want precision anywhere, you are starting with the wrong temperature sensor.

Hi PaulS

Thanks for your repply.
I want to say that I need a ramp of 5c/min, but the loop must be shorter, about 10s and check the speed each cycle.

The code needs to add 0.833 each 10s loop to the mathematic ramp, and check if the temperature is on mathematic line or not and tunrs on or off the relay for that. And if the temperature is too low (at the beginning) need a condition to add zero instead 0.83.

Hoppe not complicate.

CPalha

I want to say that I need a ramp of 5c/min

Whether you are able to increase the temperature by 5 degrees per minute, or not, has NOTHING to do with the code. It has ALL to do with the heat source and the volume to be heated.

but the loop must be shorter, about 10s

loop() should be on the order of something more like 10 microseconds.

The code needs to add 0.833 each 10s loop to the mathematic ramp

0.833 Newtons per kilometer squared?

Hoppe not complicate.

What's complicated is your tap dancing. Tap dancing has no place in your project.

Hi Paul

In labview I creat a line (law) that increases 0.833degrees c/10sec and control the relay (heater) following this line with feedback of the temp sensor.
As I am a newebie I will get an existing control temperature program, but in this case the setpoint is moving automatically.

But I not see how to do

ramp=ramp+0

loop

ramp=ramp+0.833

if temp>ramp
relay off
else ON

If temp<(ramp+5) \heater is starting heating so the ramp must wait
ramp=0

delay (10000)

something like that

delay (10000)

something like that

No, forget it. NOTHING like that.

Do not even consider using delay(). Use millis(), instead, to see if it is time to do something (different).

That is, on each pass through loop(), use millis() to get the current time. Compare that to the previous time. The difference should be used to determine the expected change in temperature.

Then, measure the actual temperature, and compare that to the previous temperature, to get the amount of change. If the actual change was less than the needed change, turn the heater on. If the actual change was more than the needed change, turn the heater off.

Expect the heater to be bouncing on and off, though, as you are not likely to get a linear change in temperature running the heater full blast or nothing and using a crappy temperature sensor.

Ok...... ::slight_smile:

I will wait for the equipement then seems I will get a very complicated thing to program.....

Thanks PaulS for your help

CPalha

Search for PID loop temperature control - many threads on this.

To get a ramp you need to feed a ramping value in to the control input of the
PID loop.

Train your PID on more demanding step-changes of temperature though, With
heating you need to be careful not to overshoot (unless you have active cooling
as well as heating).

What people are trying to say is do this for scheduling a PID loop at 10s intervals:

#define DELAY 10000
unsigned long next_pid = 0L ;

void loop ()
{
  if (millis () - next_pid >= DELAY)
  {
    next_pid += DELAY ;
    myPID () ;
  }
  // other stuff can go here, updating display, check for button presses etc...
}

float setpoint = ?? ;

void myPID ()
{
  // do the PID stuff here, it gets called every 10s
  setpoint += 5.0/6.0 ;
  // PID calcs
  // handle relay
}

Hi MarkT

Thanks for your good help.
But I was worked with the system in labview and witn a ON/OFF control and it is quite good.
With PID I am afraid that the system take many time to get the set point. I expect overshot but ±0.5C will be nothing.

Please se the picture, the problem will be at the beggining the heater will be slowly and the red ramp needs to wait for the temperature.

Thanks a lot

CPalha

If you have a working Labview program, simply use the same hardware and adapt the various labview blocks to Arduino code.

In this case, there is nothing that labview can do that the arduino cannot. More specifically, I would use the same sensor and heater, if they are working for you.

What you are really looking for is a state machine.

:slight_smile:

No, arduino works alone and it is more more simple in equipement and code (no pc).
The problem is my knowledge in that, but i will learn.

Thnaks

cpalha

Hi

here is the first version with errors.
The code increases 5 degrees /min in templaw and temp follows templaw if temp is slow, templaw waits. Please help me find the error.

Best regards
cpalha

//control a water heater beaker at 5C/min

int tempPin = A0;   // the output pin of LM35
float temp;
int led = 8;        // led pin

float templaw=5;   // the law ramp 

void setup() {
    pinMode(led, OUTPUT);
  pinMode(tempPin, INPUT);
  Serial.begin(9600);
}
 
void loop() {  
   temp = readTemp();     // get the temperature
   
   if temp < templaw + 2; {   
   templaw = templaw + 0; 
   } else {
   templaw = templaw + 0.83;//gives an increase of 5C/min
    
   }
 
    
   
   if(temp > templaw) {        // if temp is higher than tempMax
     digitalWrite(led, LOW);  // turn on led in future relay
   } else {                    // else turn of led in future relay
     digitalWrite(led, HIGH); 
   }
   
   Serial.print("TEMP: ");
   Serial.println(temp);      // display the temperature
   
   Serial.print("TEMPLAW: ");
   Serial.println(templaw); 
   
   
   
   delay(10000);
  
}


int readTemp() {  // get the temperature and convert it to celsius
  temp = analogRead(tempPin);
  return temp * 0.48828125;
   
}

Changing this:

   if temp < templaw + 2; {

to this:

   if (temp < templaw + 2) {

should help.

Very Very Thanks

Works perfectly, for now.

Best

cpalha

That shouldn't even compile without a ()!