Minor Tweaks

I've just finished tweaking the Datalogger. I changed the logging interval to 15 minutes regardless of time of day so that the graph is now completely linear.

I also changed the format of the logging file from column delimited text to CSV (Comma Separated Values) which just makes importing into a spreadsheet a little bit simpler.

I have been tinkering with a couple of op-amps to make a 'prescaler' for the temperature sensors. A voltage reference of about 2.6v-2.8v (adjustable) is subtracted from the Kelvin value voltages from the sensors to give an output that is closer to Celcius values. Gain of the differential amplifier is also set at x5 so 10-90 Celcius gives almost a full 5v swing to the input of the digitiser.

In order to get a better accuracy (smaller steps) I have also decided to invest in a different board to try as part of the Datalogger package. The new board is the Tronisoft DACIO 300. 8 Analogue inputs and two 8 bit digital IO ports, all connected to the computer via RS232. I have used this board before in another project so I'm comfortable with it.

The downside is that it needs a COM port, so I'll need to use a USB>RS232 dongle on the laptop. This slight disadvantage is more than made up for by the extra capability and resolution of the new board.

Possible expansion of the logger may include indoor and outdoor temperature sensors, monitoring of the solar panel and battery voltages and some other monitoring functions.

Sun Glorious Sun

And Centigrade Glorious Centigrade! I left the logger on for 48 hours...the data was pretty impressive!

I perhaps need to tweak the maths or the sampling interval time in order to linearise the plot. Between 9am and 5pm, the sampling interval is ten minutes. Outside those hours, it's 20 minutes so there is a nonlinearity in the graph. Alternatively, I could interpolate the missing 10 minute intervals or discard alternate readings during the shorter sampling period.

This is what the graph looks like with the 10 minute intervals removed:

I think that does the job. I'm going to compromise and rewrite the logger so it just logs data at identical 15 minute intervals over the whole 24 hour period. It takes a little 'steppiness' out of the graph, too. Until I tweak the hardware, the accuracy of the temperature measurements is +/- 1 step on the digitiser which equates to roughly 1.9 Celcius. Closer tolerance and equal intervals will mean a more readable graph. Even so, as things stand, the performance of the system can be monitored. Even at almost midnight, the tank was holding up at around 42 Celcius. I really don't need hot water then, but it does show that from when the sun comes up, the system doesn't have to lift the water temperature from a very low starting point if there has been good input on a sunny day.

Disappointing July

I don't know...perhaps August may be better, but I would have expected July to produce some decent performance on the solar thermal. Having said that, I'm not at all disheartened because all I'm using the hot water for is washing up and handwash, and for the volume of water in the calorifier, I can't moan too much. Anything above 40C is good in my book, and temperatures on a variable day like today were pushing 60C. I really ought to leave the logger on long-term and see what the performance is like over a few days. Today in moderately overcast weather, the tank got hot enough for me.

New Logger

Nothing much to report other than I have tidied up my logging app and made it look a bit more pretty.

Rain Stopped Play

The heavens really opened today. I got to the office just after 10 and although the morning had been rather bright up to that point, as I drove down to the Goat Field the clouds let rip with the most torrential rain I can recall for a long time.

Good news - the water tank started filling nicely.

Bad news - I found some leaks and rain was coming in heavily.

Good news - I think I managed to sort the leaks.

Bad news - data wasn't great today.

There was obviously some sun first thing as the tank temperature was up and the pump had obviously been running. With the VM110N modified to accept digital inputs as a 12v signal rather than a switch to ground, I can now monitor the pump control relay. Before I could do any logging, I made a few minor upgrades to the electrics.

The system simply did nothing at all between me getting the logger running just after noon and the rain drying up and the sun trying it's hardest at about 2.30 or so. Well past noon, so only at an angle to the panel, but managed to pump about 10C extra into the tank.

Real-World Logging

I couldn't have chosen a worse day! There was a lightning strike very close to the house up at The Manor yesterday, and it appears my router has gone on the fritz. As I'd emailed myself the software for the logger to download and install on the laptop, this was not an auspicious start to my day. By the time I'd switched over to the fallback internet connection and checked the van for electrical damage, the clouds had come over and the heavens opened. It was pushing 11am by this time and the panel had seen a little sun, but no action until gone 4pm. Rain for most of the day.

I have real data! It's just not very impressive-looking.

Tank temperature barely exceeded 40C, thanks to a bit of early morning sun and then hovered around the 29-31C mark for most of the day, picking up a little diffuse energy around 4.30pm when the sun had come out again...on the wrong end of the box!

What matters is the data though, not how fantastic it looks. The graph is what counts...the fact that the data is logged automatically and can generate the output required.

Number Crunching

Today being a Wednesday, I don't go over to the Manor so it's a day catching up on administration or cracking on with a few computer odds and ends.

I tackled the creation of a data logger today. Call me old fashioned (well, I am Retrotecchie, after all) but I still like Visual Basic 6.0 for knocking up 'quick and dirty' Windows-based software for my needs. One of the advantages of VB is that most of the 'hobbyist market' PC interfacing kits or modules use standard DLL libraries which are easily accessed from VB with just a few lines of code.

The Velleman K8055/VM110 USB interface modules I have lying around not only have exactly the right I/O (both digital and analogue) but the DLL is exceedingly well documented. The modules also connect to a PC via USB which is nice for the laptop I use in the office as I don't have legacy Com or LPT ports and no way of adding a PCI or PCIe I/O card.

With this in mind, I knocked up a simple data logger today. On the basis that the program can run in the background all the time the laptop is running I decided that between 8am and 5pm when the solar thermal is 'active' a ten-minute logging interval would be fine. Outside those hours, I don't anticipate the system running much (or me being in the office) so I can extend the logging interval to twenty minutes.

The system reads the two temperature sensors on the differential thermostat and converts the voltages to direct Centigrade readout. The status of the pump (running or not) is also recorded.

The daily logging is output to a date-stamped text file, the contents of which can be imported into a LibreOffice Calc (or Microsoft Excel) spreadsheet and the data converted to a graphical representation. It also counts pump cycles so I can get an at a glance status of how many times the pump has run during the logging period.

I can also toggle the digital outputs on the card just in case I want to use the card to control anything...lights, pump system or ancillary systems.

Although I developed this at home today, I've created a sample data file with 'faked' data just to see how it all works. The test board I'm using has a couple of potentiometers which I can manually tweak to simulate temperature readings and pump status. My 'faked' data looks a little like this:

This data can then be imported to a spreadsheet and converted to a graphical representation of system performance. This data can then be compared on a regular basis to see how it performs in different weather conditions or different seasons.

There's tidy. Some cosmetic refinements, and then a little work on the hardware to tidy the electronics up a little and I'm a happy bunny.