The view from April, Daylight savings time adjustment for your RTC

The boiler has worked flawless all winter, I am happy with the software and hardware but with all things mechanical there is room for improvement. I have just started my 7th ton of pellets. And I really don’t want to get into my 8th and don’t think I will have to, especially if I institute some energy conservation in the software. This is the time of year that I would normally burn what my grandmother called a “trash fire”. In her case it was some cardboard boxes from the trash and maybe an odd shaped piece of wood or two. Just enough for 3-4 hours in the evening, letting it burn out overnight since the days get up to 40°F or 50°F there’s no need for more fire than that. Later in the month most of the nights will be above freezing. But I still want to light the boiler in the evening mostly for the hot water and then turn it off at 2-3 am, so I wrote that into the software and it has gotten the consumption down to 1-2 bags per day. I also added a function in the software to change the real time clock for Daylight savings time and back automatically. It’s not fully tested but I think it will work OK.

void DaylightSavingsSchedule(){//start function
if (Year ==2013 && Month ==11 && Day ==2 && hour ==2&&DaylightTest ==0)//fall back an hour
FallBack();
if (Year ==2013 && Month ==11 && Day ==4 && hour ==2&&DaylightTest ==1)//reset flag
DaylightTest =0;
if (Year ==2014 && Month ==3 && Day ==9 && hour ==2&&DaylightTest ==0)//spring forward an hour
SpringForward();
if (Year ==2014 && Month ==3 && Day ==10 && hour ==2&&DaylightTest ==1)//reset flag
DaylightTest =0;
if (Year ==2014 && Month ==11 && Day ==2 && hour ==2&&DaylightTest ==0)//fall back an hour
FallBack();
if (Year ==2014 && Month ==11 && Day ==3 &&DaylightTest ==1)//reset flag
DaylightTest =0;
if (Year ==2015 && Month ==3 && Day ==8 && hour ==2&&DaylightTest ==0)//spring forward an hour
SpringForward();
if (Year ==2015 && Month ==3 && Day ==9 && hour ==2&&DaylightTest ==1)//reset flag
DaylightTest =0;
if (Year ==2015 && Month ==11 && Day ==1 && hour ==2&&DaylightTest ==0)//fall back an hour
FallBack();
if (Year ==2015 && Month ==11 && Day ==2 &&DaylightTest ==1)//reset flag
DaylightTest =0;
if (Year ==2016 && Month ==3 && Day ==13 && hour ==2&&DaylightTest ==0)//spring forward an hour
SpringForward();
if (Year ==2016 && Month ==3 && Day ==14 && hour ==2&&DaylightTest ==1)//reset flag
DaylightTest =0;
if (Year ==2016 && Month ==11 && Day ==6 && hour ==2&&DaylightTest ==0)//fall back an hour
FallBack();
if (Year ==2016 && Month ==11 && Day ==7 &&DaylightTest ==1)//reset flag
DaylightTest =0;
}//end function

void SpringForward(){//start function
DateTime now = RTC.now(); //get the data from the RTC
now =now.unixtime()+3600; //subtracts an hour from the time
RTC.adjust(DateTime(now.unixtime())); //resets the time to an hour earlier
DaylightTest =1; //flag variable so it won’t go back in time continously
}//end function

void FallBack(){//start function
DateTime now = RTC.now(); //get the data from the RTC
now =now.unixtime()-3600; //subtracts an hour from the time
RTC.adjust(DateTime(now.unixtime())); //resets the time to an hour earlier
DaylightTest =1; //flag variable so it won’t go back in time continously
}//end function


I am considering adding Ethernet capability

By adding Ethernet capability I can write the data I am currently collecting on the micro SD card to a browser directly. This means I could pull up Firefox and go to my Arduino’s IP Address and see the data.  This will give me the ability to read the data from anywhere on my home network as well as anywhere I can get internet connectivity, potentially allowing me to review data from a smart phone remotely. Additionally I could control relays from a remote location as well. But for now the ability to ease the data collection and monitor the process remotely will be a great first step. First I have to buy an Ethernet shield.  For those of you not familiar with Arduino this means an additional plug-in board that will stack on top of the Arduino pins.

Ethernet Shield

Ethernet Shield

Here’s a picture of just the Ethernet shield, the connection point you see on the front is the plug-in point for the Ethernet connection. This is a RJ-45 connector. I was able to get a 100 foot Cat 5 with installed RJ-45 connectors for $27 at Home Depot.

Ethernet Shield stacked on an Arduino UNO, note upper connection is the RJ-45 Ethernet connection

Ethernet Shield stacked on an Arduino UNO, note upper connection is the RJ-45 Ethernet connection

At present I have already have a prototype shield plugged into my Arduino Uno. This allows me to easily disconnect and update the Uno without disturbing any wiring connections. There are quite a few wiring connections for the RTC or Real Time Clock, the LCD display, the outside temperature thermister, the boiler water tank thermister, the Auger Feed pipe thermister as well as Relays to turn on the Auger motor and boiler tank water circulator. But when I attempted to plug in a prototype shield into the Ethernet shield there was interference with the RJ-45 connection point. The prototype shield would have grounded itself on the metal so I have ordered Stacking headers to extend the height above the shield. More when the headers arrive.


Deja Vu (it got really cold again), Test Plan

After writing a similar post on 1/15/2012 I find myself saying basically the same thing, after a -10F night the boiler has kept up. Additionally except for a 12 hour period when I made some boiler modifications the boiler has run continuously for 14 days. There are several differences however. The software is 100% better and controlling the temperature to within a few degrees. The burner is now a waterfall type burner that is much safer and runs more consistently. The hopper and auger setup is much more consistent and dependable as a worm and worm gear than the chain and sprocket setup from last year. Most significantly the burner has proved it can run on chips as well as pellets. During these colder nights it is more difficult for the burner to keep up with chips because of the density differences. The chips are much less dense and because of this the auger must feed significantly more of them. The auger motor may need to be changed to accommodate this burning however during weather that does not require so much energy the chips will burn just fine. I could have easily burned chips for most of December with no issues if they had been dry enough. Which brings me to my second topic.

A test plan. I have taken the Holidays off but it is now the new year and time to make some constant progress. To facilitate the test plan I want to make some incremental improvements in the software. The first change in the software is to gather more data to make better decisions.  To do this I am going to first add the date and outside temperature readings to both the LCD display and the data collected.  By knowing these I can correlate the feed times to temperature and see how close a relationship between them exists. Next I would like to total the run time of the auger per minute and correlate that to both outside temperature and fuel usage. Armed with this additional data I can then make various burner modifications and see the differences if any graphically. The data is good now but could be better. As you can see from the data below the software is not working properly now. The derivative portion of the formula is not contributing at all. This needs to be fixed in the software.

Data collected on SD card

Data collected on SD card


PID works!

122012PID

After tweaking the Kp and making the Ki work in the software the graph speaks for itself. The software is controlling the temperature to the set point of 140°F within a fraction of a degree for the most part. This was the last difficult piece of puzzle. I did not use the PID function in the Arduino language, instead I wrote my own with a large part of the understanding of the code coming from the excellent description by Brett Bueargard who wrote the PID library, as well as assistance from a friend who helped me understand the problem better in a spreadsheet. I now have a burner that works dependably and is modular so that I can make changes and see if I can further improve the efficiency. I now have software which will hold the temperature without worry. I plan to add a proof of fire sensor next for the mechanical part of the project, and add the ability to set the Real Time clock in the software. Onward, ever onward, but for today I think I will have a beer!


Thinking about PID control

Proportional, Integrative, Differential control.  There is a function in Arduino that implements this and I started thinking about how I would do this and if it would be appropriate.  The function, really an algorithm is all based on error and time.  In this case the error is the difference between the set point and the actual tank temperature.

All three functions Proportional, Integrative and Differential have a factor, Kp, Ki and Kd.  For example let’s calculate each portion of the formula starting with the proportional contribution Kp, if the current temperature of the tank is 100°F and the set point is 140°F the error is 40.  The integrative portion of the formula adds the contribution of the error over time.  This would be the Ki factor multiplied by 40 and added to the previous Ki*error for every time period.  The differential portion is the Kd multiplied by the difference in the tank temperatures or in other words the tank temperature at the beginning of the time period  minus the tank temperature at the end of the time period.  Let’s take some of the data collected by the OpenLog microSD card and take a stab at this in Excel. We’ll assume Kp=6, Ki=.6 and Kd =.2. The time period is one minute.

Raw data imported into Excel with PID data calculated

Raw data imported into Excel with PID data calculated

Now in practical terms how is the the fire being controlled now?  The auger time is being controlled.  Of course practically the fire must not go out so there is a minimum time the auger must run, since in this program the auger is on a fixed time of 5 secs this really means that all of the control comes from varying the time the auger is not running.  But again the fire can’t go out so I figure the max amount of time between the fixed auger feeds of five seconds is forty seconds.  So that is the slowest the fire can go.  How fast can it go?  Well theoretically the feed could run continuously but again we are dealing with a chemical process that cannot simply absorb 100% fuel feed.  In this case the auger motor added a practical aspect by limiting the feed to a duty cycle of 50%, so the maximum time that the feed can be on is half the time.

Since the PID control is based on time periods and the data collection time period is one minute,lets choose a time of 1 minute for argument.  In one minute at max run the feed will be on 30 seconds and off 30 seconds.  In one minute at min run the feed will be on for 5 secs, off for 40 secs, on for 5 secs and then off for the remaining 10 seconds of the minute.  So again we don’t control the on time only the off time and the difference between the max on time (min off time) and min on time (max off time) is 30 secs on, 30 secs off for the max and 10 secs on and 50 secs off for the min.   So the only control between full bore and idle is the difference between 50secs and 30 secs or 20 secs per minute.
 
This explains some of the challenge,  the other challenge is the inertial effect of the combustion reaction especially if unburned fuel has built up.  So now that the PID output has been calculated I’m having a hard time wrapping my mind around how this would translate to control of the time, I know I could set up a simple proportion between the PID output and the 0-20 scale of  auger off time dwell.  However in this example the PID output  increases as the error decreases.  I guess that’s the beauty of a spreadsheet I will play around with Kp, Ki and Kd to see if I can get this to work a little better.


Software changes to control underdamped Setpoint control

After running for a few days I have been happy with the amount of holes in the bottom of the burner, the ash level when running does not get higher or lower.  However the fuel usage is a little higher than I thought it would be and the program does not hold the set point temperature as well as I would like.  The graph shows the interaction of the excess fuel usage and the set point.  At times the boiler should be idling along with very little fuel feed, the program should be able to determine the fuel usage needed to control the temperature to the set point.

Under damped control

Under damped control

You can see the 140°F horizontal grid line, the set point is currently 140°F. The integral of the area over that line is excessive fuel usage. However that’s not the only issue, the second issue is the amplitude seems to grow larger until approx. 121 minutes.  At that point I shut down and started a new software change.    You can see the slow recovery as I had to relight the fire and then the software starting correcting earlier, so in short more software changes are in order.    The challenge is to build self correcting software since the whole goal of this project is to burn chips and that will require the software to deal with different energy densities.  I’ll make a few more software changes and post another graph soon.


More Testing, another day, another graph

I rebuilt the burner yesterday added more air holes in selected areas and tried to stop up the misc air leaks to see if that

Tank Temperature vs. Time in minutes

Tank Temperature vs. Time in minutes

would add more power.  I’ll let the graph speak for itself.   Note the issue at 45 or so minutes in where the temperature started to drop.  At this point the sawdust bridged so badly it wasn’t feeding any fuel.  After I poked the sawdust in the hopper, the temperature continued to rise.  I had to continue to poke the pile to get the feed rate to be somewhat normal.  Looks a lot like yesterday’s graph, so I am thinking about adding some additional air through a forced draft fan on the front end of the process.   Once again the burner did do the job but slowly and until approx. 379 minutes or a little more than 6 hours into the test did the temperature rise past the point where the circulator turned on.  I measured the chamber pressure, in this case vacuum and it measured .1″ H2O so additionally I am wondering if I need a larger exhaust fan as well.