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PrinceNai
Joined: 31 Oct 2016
Posts: 452
Location: Montenegro
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| K40 laser water control |
 Posted: Sun Apr 21, 2019 9:35 pm |
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Dear All,
I recently bought a cheap laser cutter, which will be operated by my friend that has time, will and ideas of what to do with plastics. After spending some time on the net we decided to make a water cooling system that is a little better than just relying on the temperature inertia of 10l tank of water. The idea is this:
The controller will have the control over a peltier driven cooling tank, it will measure two temperatures and will be checking if the water pump is working by means of a Hall effect water flow sensor. All the data will be shown on an 4x20 LCD, with a piezo buzzer to wake up the operator if something goes wrong. Two things can. Either the temperature of the water is too high for some (as yet unknown) time or the pump dies. In either case it will shut down the laser tube.
It is a very simple project with respect to the code, so I don't need any coding assistance, at least not so far. What I would need is some input of where (the water tank definitely, the other location is probably at the exit of the laser tube) and how fast I should measure the temperature. Maybe PID control is needed. It is also meant as a project for all potential laser enthusiasts that read this.
I know I'm stretching the usage of this forum, but I've found the ideas and replies here very useful for uncounted number of times and that is why I'm asking and posting this. So if you administrators find this out of the playing field, just delete the topics and forgive me for wasting your time.
I will make a PCB board for this that will accept 20 and 40 pin PIC-s. I only need one, but the Chinese guys will send me at least 20 for the same price. If there will be any interest, the rest of them will be available for free, just for the price of shipping.
I whipped together a skeleton of a code for the controller (the temperature measuring is working 100%), just a sketch. It uses just the first temperature sensor. It is still in a process of going from floats to integers, flow sensor hasn't arrived yet and the program is missing the timing, output actions and very likely some possible "problem" scenarios. That is where your input would be much appreciated. How to do it correctly.
| Code: |
#include <thermo_1820.h>
#include <string.h>
#include <i2c_Flex_LCD_driver.c> //LCD driver
#include <1wire_2_sensors.c>
#include <ds1820_2_sensors.c>
//float Temperature1 = 0; //temperature from 1820 in deg. Celsius
//float Temperature2 = 0; //temperature from 1820 in deg. Celsius
signed int16 Temperature1 = 0; //temperature from 1820 in deg. Celsius
float Temperature2 = 0; //temperature from 1820 in deg. Celsius
#define WATER_TOO_HOT 220
// *********************** FUNCTIONS ******************************************
void Service_Temperature1 (){
// Temperature1 = DS1820_read1(); // change to correct DS1820 pin in 1Wire.c
DS1820_read1();
Delay_Cycles(1);
Delay_ms(30);
lcd_gotoxy(1,1);
Delay_ms(30);
lcd_putc("Water tank: ");
Delay_ms(30);
printf(lcd_putc,"%3.1w", Temp3);
Delay_ms(30);
lcd_putc('\xDF'); // degree sign, works!!!
Delay_ms(30);
}
void Service_Temperature2 (){
Temperature2 = DS1820_read2(); // change to correct DS1820 pin in 1Wire.c
Delay_Cycles(1);
Delay_ms(30);
lcd_gotoxy(1,2);
Delay_ms(30);
lcd_putc("Laser tube: ");
Delay_ms(30);
printf(lcd_putc,"%3.1F", Temperature2);
Delay_ms(30);
lcd_putc('\xDF'); // degree sign, works!!!
Delay_ms(30);
}
#INT_TIMER1
void TIMER0_isr(void) {
output_toggle(PIN_B5);
}
void main() {
setup_timer_1(T1_INTERNAL|T1_DIV_BY_4); //50 ms overflow
enable_interrupts(INT_TIMER1);
enable_interrupts(GLOBAL);
// port_b_pullups(true);
lcd_init(); // init LCD
Delay_ms(100);
lcd_putc('\f'); //CLEAR lcd
lcd_gotoxy(1,1);
Delay_ms(100);
lcd_putc("K40 WATER CONTROL");
delay_ms(2000);
lcd_putc('\f'); //CLEAR lcd
lcd_gotoxy(1,1);
while(TRUE){
Service_Temperature1 ();
Service_Temperature2 ();
// ...........CHECK WATER TEMPERATURE AND TURN ON COOLING IF NEEDED...........
if(Temp3 > WATER_TOO_HOT){
output_low(PIN_C6);
lcd_gotoxy(1,3);
lcd_putc("WATER COOLING IS ON ");
}
else{
output_high(PIN_C6);
lcd_gotoxy(1,3);
lcd_putc("WATER COOLING IS OFF");
}
// ................ CHECK IF THE WATER PUMP IS WORKING.........................
if(TRUE){
lcd_gotoxy(1,4);
lcd_putc("WATER IS CIRCULATING");
}
else{
lcd_gotoxy(1,4);
lcd_putc("PUMP IS NOT WORKING ");
}
// .............. MEASURE FOR HOW LONG THE WATER IS TOO HOT ...................
// ............................................................................
}
}
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Regards,
Samo |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19219
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| Posted: Sun Apr 21, 2019 11:27 pm |
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I'd do two things:
I'd measure the temperature at the exit of the tube.
I'd measure the flow _at the same point or just after_.
This way, the water has to be flowing through the tube to be detected
by the flow meter, and must pass the temperature sensor to be detected
by the meter.
If you detect before this point, there is always the possibility of a leak
between the flow detection point and the temperature sensor.
For simple 'emergency' detection, you don't need PID. This would be
required for control.
Your logic seems slightly wrong. You turn off the tube if the temperature
is too high, but not if the water pump fails. Remember if the pump
fails there will not be water flowing to the temperature sensor. So
there may well not be an over temperature reading....
So logic:
Test if flow?.
No. Cut laser.
Yes. Test if temperature outside threshold?.
Yes. Cut laser.
No. Run Laser.
Now I say 'threshold'. You might want to also cut the laser, if the
temperature reads as <1C. This could imply water would be frozen, or
that the temperature sensor is disconnected. Either could be failure
reasons... |
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temtronic
Joined: 01 Jul 2010
Posts: 9102
Location: Greensville,Ontario
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| Posted: Mon Apr 22, 2019 5:15 am |
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general comments
1) use 2 flow sensors. relying on just ONE sensor is what caused the MAX8s to crash. I'd put 2nd at the tank outlet. If they're calibrated the same, the flows should be the same.
2) PID is not needed. simple bang-bang controller is fine.If you have an RTC, have it send a 1HZ interrupt. this 'triggers' the 'read the temp sensors' routine,update the display, etc. Temperature is usually a long term 'event', IE slooooow, you don't need 1,000s of updates. I run my solar controller and bldg heating systems this way since the 16C84 with no complaints.
3) a 'power up- selftest' function is needed. Confirm water flows, temp sensors agree, etc. BEFORE running 'main()'.
4) use separate pins for the temp sensors. Makes for simple coding, easier wiring.
Jay |
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PrinceNai
Joined: 31 Oct 2016
Posts: 452
Location: Montenegro
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| Posted: Mon Apr 22, 2019 5:56 am |
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| Quote: |
You turn off the tube if the temperature
is too high, but not if the water pump fails
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As I said, the code is more of a sketch, far from finished. It will shut down the K40 in both cases, independently. Water too hot or no flow ---> shut down.
| Quote: |
a 'power up- selftest' function is needed. Confirm water flows, temp sensors agree, etc. BEFORE running 'main()'.
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Maybe that won't be needed, because upon power-up the pump should be working, but not the laser tube itself. It fires after one loads the shape to be cut and presses go button, and that takes some time. My control is active in 2 or 3 seconds and will be monitoring things way before that.
| Quote: |
use separate pins for the temp sensors.Makes for simple coding, easier wiring.
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That is the way it is done already. Two DS1820 sensors, two separate pins. Sorry I didn't send the whole code, you couldn't see that.
Two flow sensors are a good thing and I'll place them as you suggested, at the exit from the tube. I won't use RTC, instead I'll just use timer interrupt to make the program execute measurements and any actions approx. once every second. And WDT every 2,3s to restart if it hangs. I also think that it'll work without PID. It is a 40W laser and I have 120W cooling elements (two peltiers glued on a small water tank). The water will be cooled to some 18 degrees Celsius and laser will shut down when it comes above 20. The cooling will start as soon as it goes above 18. I'll add the check for below zero temperature, but as long as I pay the bills, that won't happen :-). |
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PrinceNai
Joined: 31 Oct 2016
Posts: 452
Location: Montenegro
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| Posted: Mon Apr 22, 2019 6:07 am |
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| Once again for below 1 degree. That is the reason for two temperature sensors, but maybe I'll throw in the third. As long as two of them agree on the temperature, I'm fine. |
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temtronic
Joined: 01 Jul 2010
Posts: 9102
Location: Greensville,Ontario
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| Posted: Mon Apr 22, 2019 7:08 am |
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re:
upon power-up the pump should be working
hmm, 'should be'. you need to confirm before, never assume. I had to replace a 10K$ xray tube as someone 'assumed' the safety circuitry was functioning.
do you use RO water for cooling ? |
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PrinceNai
Joined: 31 Oct 2016
Posts: 452
Location: Montenegro
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| Posted: Mon Apr 22, 2019 9:16 am |
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When the machine is powered up, the pump starts pushing the water around, but the laser itself isn't on yet. Within 2 seconds I'll have the temperatures and the indication of the water flow, so no way the laser will fire if the pump isn't working. Maybe I should add a few minutes delay at startup to ensure that the water is mixed and at the correct temperature, both in the tube and in the tank.
I'm using distilled water and am thinking of adding a TDS meter. |
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