BOILER MONITOR
My old oil-fired central heating boiler was circa 1974 vintage and the ignitor was becoming intermittent, which meant that if it didn't light, it tripped out. I spoke to Nu-Way who manufactured the burner unit and they said something unpublishable and "...that should be in a museum!". With little hope of repair, I had two options available
- continue having the wrath of the rest of the family fall on me whenever the boiler failed to start or
- replace the boiler
I chose the latter. After a period of investigating boiler manufacturers and installers, I finally settled on a 32/50 (kW) oil-fired boiler by Worcester Bosch. This was installed in a day and while not costing any less to run, despite it being 93% efficient, it does heat the house very quickly and to a temperature higher than the old boiler ever could.
The boiler is located in a building that's separate from the house and I was intrigued to determine how long the boiler was firing and also when the house thermostat had cut in. I bought a Velleman USB I/O card and some mains relays from Maplin, wrote a couple of Windows programs in C, found a spare Dell GX11 PC in my store and very quickly had a working boiler monitor. One program runs continuously, collecting data from the I/O card and writing it to disk. The second program runs as a CGI program within IIS and generates an SVG image from the collected data. The graph below shows a typical day's usage.
The graph is generated on-the-fly and shows the "on" and "off" periods for each channel that it's monitoring. Two channels are being monitored here but the card will support up to five digital inputs. I built a unit that sits between the card and the mains supplies for the pump and boiler. This is limited to four channels but only because that's as many relays as would fit the die-cast box (photos to follow). You could use a third channel to monitor the mains supply, providing the PC was on a UPS. The image contains three icons that are links to the previous and next day's data and a refresh button for the current day. The icons change colour with the context, so if the day being displayed is not "today" the refresh icon is greyed-out and, likewise, if there is no previous or next day's data, those icons are grey and inactive.
The block diagram below shows the general design of the system. A UPS provides reliable power to both the boiler, pump and PC so that power failures can trigger an SMS message to one or more mobile or fixed numbers.
SVG is a standard web language for graphical images and it has the benefit of being human-readable, which is an essential aid during development and debugging. Most modern browsers will deal with SVG, though if you're using Internet Explorer you might need to install the Adobe SVGview plug-in. (Why I use SVG.)
The Velleman card is very easy to set up and get going. There's lots of example code in Basic, VB, C++ and so on on the Internet but none that I could find for standard C, my preferred language. This was a potential problem because the card is supplied with a DLL but no .LIB file, so my C linker was going to complain about that.
The purpose of the LIB file is to provide information to the linker about the functions in the corresponding DLL. The linker would normally include this information in the program's EXE file. In the end I used pointers to each function that I intended to call and resolved the addresses of their locations at run-time, so the linker did not need to know about the functions at link time. There are four steps to obtaining the functions' addresses:
- create a type definition for each unique function type, that is, its return type and argument types
- using the type definition, define pointers to each function using its name. The name you choose to use doesn't have to match the actual name of the function in the DLL, but not doing so can cause confusion and is poor practice.
- load the DLL by specifying its path and filename in a call to LoadLibrary()
- obtain the address of each function in the DLL and assign it to the local name
The following example code in C shows the various steps involved:
// One typedef for each unique combination of return and argument types
typedef void (CALLBACK* LPFNDLLFUNC0)(void);
.
.
// Define each function using its corresponding typedef
LPFNDLLFUNC0 ReadAllDigital;
.
.
// Load the DLL
hDLL = LoadLibrary("K8055D.dll");
.
.
// Store a pointer to the address in the DLL of the function
ReadAllDigital = (LPFNDLLFUNC0)GetProcAddress(hDLL,"ReadAllDigital");
.
// Now you can use the function by calling it as ReadAllDigital()
THE DATA RECORDING PROGRAM
The data recording program (K8055log.EXE) runs continuously and records any changes to the digital inputs. It only writes a record to the data file when a change occurs and this means that the data files are fairly small and, for this application, less than 2K bytes per day. The filename comprises the date that the data were recorded and each data record is a simple timestamp and the current status of each channel. An example of recorded data is shown below:
00:00:00 0 0 0 0 0
04:59:05 1 1 0 0 0
05:21:49 1 0 0 0 0
05:32:55 1 1 0 0 0
05:38:17 1 0 0 0 0
05:50:37 1 1 0 0 0
05:55:59 1 0 0 0 0
06:08:35 1 1 0 0 0
06:13:55 1 0 0 0 0
K8055log starts by reading a configuration file, which can be used to set up rules for what to do when a channel goes on or off. Typically, this can be used to send a text message to someone about a power failure, etc. All that's required is a mobile handset connected by cable or Bluetooth and to type the port, mobile number and appropriate message in the configuration file.
The program needs to deal with channel settings spanning midnight and this requires synchronising two data files. It does this by checking to see whether the file it is about to write to exists, if yes it just writes the data, if not it writes a record for midnight with the current settings as the first record in the new file before writing the new settings that triggered the write. There is no corresponding midnight record in the previous day's data file but the plotting program deals with this by extending, to midnight, the last data recorded.
THE GRAPH PLOTTING PROGRAM
The graph plotting program (BoilerMonitor.EXE) runs as a CGI program under Microsoft IIS, thjopugh you could use Apache or something similer. With no arguments the program generates a graph for today's data. It reads a configuration file to obtain some parameters such as its own URL, the path to the local data files, how many channels to display, plot style options and whether to draw graphpaper.
The program draws the axes, labels and graph paper; then it reads the data file and generates the "ON" graph for each channel. It then determines whether the previous and next day's files exist and creates the icons and links if appropriate.
The program also inserts comments into the SVG so that human readers can keep track of what is being drawn. One of the settings in the configuration file is to create additional diagnostic comments in the SVG source to assist in debugging future revisions of the program.
PARTS LIST
The list of parts required is shown in the table below. The Velleman I/O card comes with its own USB cable. I have used RJ45 sockets and a patch cable for the connection between the I/O card and the relays so that I can put the PC remote from the boiler, but you could make a direct connection or put the card and relays in a larger die cast box and have just a USB connection to that.
The connections between the mains inputs and the relays are single core 1mm2 stranded cable terminating at screw terminals at the relay but could be soldered or crimped spade connections at the IEC socket. The internal cabling is bound together with some small plastic tie-wraps.
| Description | Quantity | RS part number | Maplin part number |
|---|---|---|---|
| Die-cast box 120x185x80 | 1 | N72FK | |
| 240V relay - 8-pin | 4 | JG60Q | |
| Relay socket - 8-pin | 4 | JG54J | |
| IEC C14 mains socket (chassis type) | 4 | HL15R | |
| RJ45 Krone IDC metal receptacle (chassis) type | 1 | 450-9062 | |
| Velleman K8055 card | 1 | L92BL | |
| 3mm nuts, screws, washers | various | ||
| 1mm single core stranded wire | |||
| spade connectors (optional) | |||
| tie wraps |
NEXT STEPS
The next step is to use Dallas (now Maxim) 1-Wire thermometers to record temperatures at various points on the system and plot them on the graph with a second Y axis, or as a separate graph. I plan to record outside air temperature and inlet and outlet water temperatures on the boiler.