#3 readme updates

#3 readme add PID Usage Example w/ charts

README.md

@@ -6,7 +6,7 @@ A PC fan controller using temperature sensors/thermistors, for Teensy 3.x USB De
 
 Supports up to 6 PWM (4pin) fans, and up to 5 temperature sensors (supply water temp, return water temp, case temp, aux1 temp, aux2 temp). Each fan may individually operate in PID, percent-table, or fixed-speed (percent) control modes.
 
-Primarily designed to control radiator fans (4pin/PWM) for a PC water cooling loop, using feedback from a water supply temperature sensor. Configurable to prefer quiet-but-safe operation in all cases.
+Primarily designed to control radiator fans (4pin/PWM) for a PC water cooling loop, using feedback from a supply water temperature sensor. Configurable to prefer quiet-but-safe operation in all cases.
 
 Prototype hardware (supporting 6 fans and 4 sensors) is described in the *Hardware* folder.  Schematic and PCB (Gerber files) will be provided later.
 
@@ -24,19 +24,20 @@ Note: it is possible to connect the Micro USB port to an internal motherboard US
 
 The PID controllers satisfy a temperature setpoint, by changing fan PWM duty cycle(s).  By default, all fans operate in PID mode for supply water temperature control.
 
-The controller may operate up to 4 PID controllers, one per the following temperature sensors: supply water temp, case temp, aux1 temp, and aux2 temp.
+The fan controller may operate up to 4 PID controllers, one per the following temperature sensors: supply water temp, case temp, aux1 temp, and aux2 temp.
 
 
-#### Supply Water Temperature Control
+#### Supply Water Temperature Control / Setpoint Adjustment
 
-A supply water temperature setpoint reset schedule is enabled by default, to adjust for room and/or case temperature changes. By default, the setpoint adjusts between 28 and 31 degC, at 0.5 degC increments. If a case temperature sensor is connected, the reset schedule can be limited by a difference between water supply and case temperature (allowing fan spin-up when case temperature does not change).
+TODO
 
+A supply water temperature setpoint reset schedule is enabled by default, to adjust for room and/or case temperature changes. By default, the setpoint adjusts between 28°C and 31.5°C, at 0.25°C increments. If a case temperature sensor is connected, the reset schedule is limited by a difference between supply water and case temperature (allowing fan spin-up when case temperature does not change).
 
 ### Percent-Table Mode
 
-Each fan may be individually configured to operate using its own *Temperature to Fan Percent table*.  This is like BIOS custom fan configurations.
+Each fan may be individually configured to operate using its own *temperature to fan %-table*.  This is like BIOS custom fan configurations.
 
-Any one of the five temperature sensors, or DeltaT (return temp - supply temp), may be used as the temperature source.
+Any one of the five temperature sensors, or DeltaT (return temp - supply temp), may be used as a temperature source.
 
 
 ### Fixed Mode
@@ -50,12 +51,54 @@ Each fan may be individually configured to operate using a fixed speed (percent)
 
 [Teensy Fan Controller UI (Qt5)](https://github.com/mstrthealias/TFC-ui): provides a user interface to configure and monitor the fan controller.
 
-
-### Linux Kernel modules (hwmon)
+### Linux Kernel module (hwmon)
 
 To be published (liquidtux).
 
 
+## PID Usage and Example
+
+The default configuration works well on a PC with a water-cooled CPU and an air-cooled GPU:
+
+- Uses a supply water temperature and case temperature sensor
+- Controls supply water temperature to 2-3°C above case temperature
+- Fan output percent is generally between 45%-60%, unless CPU is loaded
+- If case temperature is within 2°C of supply water temperature, the setpoint will increase in 0.25°C increments when fans are spinning faster than 60% for 20 seconds
+
+
+For example, the fans are controlled to keep supply water temperature at setpoint:
+
+![Example 1.1](doc/images/ex1.1.jpg?raw=true 'Example 1.1'){:height="480px"}
+
+
+In the same dataset as ![Example 1.1], and only plotting fan RPMs and DeltaT (return temp - supply temp), observe the fan speeds closely tracking DeltaT (which represents CPU load in the following example):
+
+![Example 1.2](doc/images/ex1.2.jpg?raw=true 'Example 1.2'){:height="480px"}
+
+
+Next, an air-cooled GPU is used for about 30 minutes, showing *setpoint adjustment* keeping fan speeds within the configured range:
+
+![Example 2](doc/images/ex2.jpg?raw=true 'Example 2'){:height="480px"}
+
+
+The same behavior is observed, except caused by room temperature changes, in this example:
+
+![Example 3](doc/images/ex3.jpg?raw=true 'Example 3'){:height="480px"}
+
+
+When only the CPU is loaded, the setpoint temperature does not change, and the fans speed up as needed:
+
+![Example 4](doc/images/ex4.jpg?raw=true 'Example 4'){:height="480px"}
+
+
+### Considerations
+
+A case temperature sensor should be used if using *setpoint adjustment* with PID supply water temperature control:
+
+- When under load and without a case temperature sensor, the setpoint will increase to the maximum before allowing fan speedup
+- Without a case temperature sensor, setpoint adjustment may achieve the same result as using a supply water *temperature to fan %-table*
+
+
 ## Configuration
 TODO