Add the Calibration sub-chapter

mainpart.tex

@@ -106,6 +106,15 @@ The data from the could data stream are then visualised on the server node via p
 
 The web interface also contains a button for shutting the appliance on or off (by controlling the electromechanical relay K1). It consists of simple ON/OFF button that changes its value accordingly to the relay's state. It also uses the mentioned \gls{ddns} service to contact the server node.
 
+\subsection{Measurement calibration}
+
+Since the client's node is performing measurements of physical quantities, it is reasonable to perform the initial calibration, to make the device as accurate as possible. Since the actual measuring unit, the MAX78700\cite{online:MAX78700}, is an \gls{adc} converter, it cannot provide the results in an actual Volts and Amperes. To be able to interpret the 24-bit number obtained from the the conversion process, we have to multiply it by calibration constants. They depend on the resistors surrounding the converter.
+
+This process is also outlined in the reference design\cite{online:SONOMA} provided by Maxim, displaying the calibration constants tailored for the configuration suggested by it, along with the formulas to do the calculations.
+
+The calibration performed in the laboratory resulted in similar, but not entirely equal calibration constants. The difference could be caused by a little bit different lengths in \gls{pcb} tracks and different length and material of the conductors, with respect to the reference design, which needed to be taken into consideration.
+
+
 \subsection{Possible future improvements}
 The most crucial thing to improve is to make the client node's start reliable. The ESP-12E module sometimes won't start. After this problem has been resolved, one can move on to some other issues, but not before.
 
@@ -113,7 +122,7 @@ It is possible to fulfil all the failed requirements due to inability of accessi
 
 Speaking of a \gls{pcb} iteration, another opportunity to improve the \gls{pcb} design lies in utilising the MAX78615 in-built relay controlling mechanism, utilising one of its free multio-purpose \gls{io} pins. Fundamental part of responsibilities of the \gls{ic} is to track the phase shift, thus being informed about the zero-crossing\cite{chappell2013introduction}. Relay switching locked to the zero-crossing allows for a graceful start ofthe appliance. This is helpful in preventing damage to some sensitive appliaces when started at the point of mains line voltage peak, such as incandescent light bulbs\cite{dilouie2008lighting}. Relay is also not essential for actual measurements, so it could be removed from the system altogether to save some cost and space, in applications where the relay is not needed.
 
-It would be really helpful to address the cosmetic issues, outlined back towards the end of a sub-chapter \ref{ss:problems}. Also, to reduce the cost, the programming circuitry described in sub-chapter \ref{ss:schematic_pcb} could be removed from the PCB and moved onto the programmer itself. To reduce the size, the fuse could be replaced by the smaller size one, or even better, the miniature resettable \gls{ptc} one, proposed back in the chapter \ref{ss:hw}. The connectors for mains could be replaced by fast-on type to simplify the final assembly process. The crystal Y1 could be replaced by a miniature resonator to reduce the size too.
+It would be really helpful to address the cosmetic issues, outlined back towards the end of a sub-chapter \ref{ss:problems}. Also, to reduce the cost, the programming circuitry described in sub-chapter \ref{ss:schematic_pcb} could be removed from the PCB and moved onto the programmer itself. To reduce the size, the fuse could be replaced by the smaller size one, or even better, the miniature resettable \gls{ptc} one, proposed back in the chapter \ref{ss:hw}. The connectors for mains could be replaced by fast-on type to simplify the final assembly process. The crystal Y1 could be replaced by a miniature resonator to reduce the size too. The linear voltage regulator could also be replaced by a smaller one, since the power consumption across whole node is not that high overall.
 
 There is always a room for improvement, but the last bigger proposed one is to completely remove the GL.inet board from the system. It was included mainly for research and practice reasons, not so much to provide some necessary functionality. If we wanted strictly cloud-connected client devices, given there is a trend in increasing count of such a devices, this would reduce the cost and complexity. Such a change would require the client devices to be connected to the Internet all the time and to move the web server from the GL.inet (server node) to some other place, preferably where the could storage is hosted. It would also eliminate the need for an external \gls{ddns} server.