Changes by last author:
Changed:
| Even on v3.2 that is assembled to a very high level, the EGT parts are not on (pads left empty). The circuit itself is simple: |
| Even on v3.2 that is assembled to a very high level, the EGT parts are not always populated (- except the assembled controllers). The circuit itself is simple: |
|
but the
* probe * AD597AR chip * special connector (to eliminate the error caused by temperature difference between EC.. connector and AD597AR chip) are expensive and require some attention. Not surprising, that usually just an EGT meter is sold for higher price than the whole GenBoard/VerThree |
|
See [Rob's EGT guide]
Short checklist (see table below for details): * supply for AD597AR * sensor (or compensational cable) wires connected (green+ to AD597pin1 and white- to AD597pin8). A(n optional) capacitor between them filters noise. * make sure pins 1,3,4 of AD597 are connected, using the SMD pads and some wire (note: pins 8,3,4 would be just as fine). This provides a solid ground for the circuit input * AD597 output (pins 5,6 connected) connected to MCP3208 via 2 resistor + 1 cap voltage divider and filter. This is onboard since v3.2 so requires little to no attention. |
|
|| EGT+ connection || green (+) wire from the sensor goes to pin1 || pin1 vs pin8 should measure 0mV in diode-check mode (upto +1mV if the sensor is connected and you heat the sensor tip 25C) || ||
|| EGT- connection || white (-) wire from the sensor goes to pin8 || pin1 vs pin8 should measure 0mV in diode-check mode (upto +1mV if the sensor is connected and you heat the sensor tip 25C) || || |
|
|| EGT+ connection || green (+) wire from the sensor goes to pin1 || pin1 vs pin8 should measure 0mV in diode-check mode (upto +1mV if the sensor is connected and you heat the sensor tip 25C above the cold junction temperature) || ||
|| EGT- connection || white (-) wire from the sensor goes to pin8 || pin1 vs pin8 should measure 0mV in diode-check mode (upto +1mV if the sensor is connected and you heat the sensor tip 25C above the cold junction temperature) || || || filtering cap || 100..220..1000..2200nF cap between EGT+ and EGT- (easiest on the board bottom side, right where the compensational cable is soldered to the header) || - || EGT reading becomes more stable || |
| It doesn't make sense to care too much about EGT reading on LCD until the above steps are completed (pin6 voltage depends on temp). |
| Default firmware release is compiled with MCP3208_EGT1=4 . This is valid for v3.2. However v3.0-v3.1 users will add MY_CONF += -D MCP3208_EGT1=5 to my_make and recompile (alternatively, it is OK to physically connect the EGT amplified output (with a small solder-blob) to both channel 4 and 5 (mcp3208 pin5 and pin6). |
| AD597 output (10V for 1000C) is divided with 2 resistors so the mcp3208 can measure it (max range is 5V). |
| It doesn't make sense to care too much about EGT reading on LCD until the above steps are completed (pin6 voltage depends on temp - or EGT input). |
|
----
Calibration |
|
** v3.2 (R83=100k, R84=75k) since there is a cap on mcp3208 input that enabled us to use these high resistor values (little current consumption). Division is * 3/7.
** v3.0, v3.1 : (R83=2.7k, R84=2.7k) although division is * 1/2 , not same as for v3.2 (someone can find better matching values under 35k that are available in the rescue kit ??) 22k:33k is closest prolly... |
| AD597 output (10V for 1000C) is divided with 2 resistors so the mcp3208 can measure it (max range is 5V). config.egt1_cal can be adjusted to show proper readings. |
|
----
MCP3208 to LCD |
|
* v3.2 (R83=100k, R84=75k) since there is a cap on mcp3208 input that enabled us to use these high resistor values (little current consumption). Division is * 3/7.
** egt1_cal=0x49 (decimal 73) is most likely ** egt1_offs=00 * v3.0, v3.1 : (R83=2.7k, R84=2.7k) although division is * 1/2 , not same as for v3.2 (someone can find better matching values under 35k that are available in the rescue kit ?) might be 22k:33k closest. Some uses a piggyback cap that allows exact same (high value 100k and 75k) resistor values that are used since v3.2. ** egt1_cal=0x3F (or 0x3E decimal 63 or 62) is most likely, but do verify since different dividers were used ** egt1_offs=00 Calibration method |
|
In lcd_display.c channel 5 is written (from the valid real channel numbers 0..7).
<code> mcp3208_data[5]; ... read_mcp3208(5); </code> The real channel 5 is confusingly (in eagle library or mcp3208 datasheet) named MCP3208_CH6 (from CH1..CH8). Anyway, 5 in the code reads pin6. (0 in the code reads mcp3208 pin1, ...etc... 7 in the code reads mcp3208 pin8) Since EGT1 out goes (after divider) to mcp3208 pin5 on v3.2, this is the only change since v3.1. To get good LCD reading you can * change the code: write "4" instead of "5" to read mcp3208 pin5 * or connect the mcp3208 pin5 and pin6 (since you most likely not use pin6 for anything else anyway): the leftmost pins on the 2x2 througholes right-upper relative to AD597 are perfect for this |
|
* connect input voltage to the EGT input. Eg. a 2*1.5V battery pack and voltage divider is perfect. Eg. 150k and 1k gives division of 3V/151=19.86mV.
** 10..30mV is best ** green (AD597pin1) is + ** white (AD597pin8) is - |
|
TODO:
* config.egt1_cal units, and calibration hints (verify with DVM) |
| Example |
|
Let's say you measure 19.7mV on EGT input that you applied with the improvised voltage divider. If board temperature is 26C, the egt1_cal should be adjusted until EGT reading is appr. 26C + 19.7mV/(40uV/K)=26C + 492.5K = 518.5C In practice 510 .. 527C is perfect.
I usually start with egt1_cal=0xFF, read the value and adjust it in one step with a simple calculation. Or egt1_cal=0x49 and confirm the read value is perfect. |
| These seem to be old notes, everything has been standardized since and applied to the pick-n-place manufacturing |