Artisan and Multiple Gas Gauges
The gas gauge in coffee roasting is the same as the gas pedal in driving - it determines how much energy is sent to the burners. Roasting profiles are based off very precise settings. The gas gauge included on my roaster was of little value because it had too large of a range. I've since replaced it and am having some fun incorporating it into the software.
Both the middle and right gas gauge are transmitters, so I can grab the output and send to a Phidget.
Artisan-Scope, the donation-supported coffee roasting platform can then use the Phidgets to display the data.
Calibrating the gauges was a bit of fun. The mechanical gauge reads an accurate gas pressure, but the transmitter basically reads a current in mA. This needs to be converted back so that both measurements are the same.
- Map out a bunch of datapoints (minimum of 3, preferably 5+) and plot them. I used Excel. X-axis should be mA and Y-axis should be inches of H2O. Verify that they form a (relatively) straight line.
- Assuming you form a line, which both of my Dwyer gauges did, you can figure out the equation of the line, or y=mx+b.
- Using 2 of the measurements (I used 2 in the middle), find the slope (m) by (Y2-Y1)/(X2-X1). Then, solve for the y-intercept (b) by putting in a single point as (Y3)=m(X3)+b
- The output allows you to display the Gas in Artisan as inches of H2O by having y2(x) on the Phidget Device be: mYn+b (Yn is the y1(x)
- Mine expressions worked out to be:
|
Device |
Label 1 |
Label 2 |
Y1(x) |
Y2(x) |
|
Mill City Probes |
Y1: Bean Temp |
Y2: Exhaust Temp |
n/a |
n/a |
|
Virtual Used for First Crack Alarm |
[Y3] toFCs |
[Y4] afterFCs |
pFCs |
t-t{FCs} |
|
Phidget TNO1101 Roaster Air Temp |
[Y5] Air Temp |
[Y6] not used |
||
|
Phidget TMP1101 Port 1 Dwyer 605-20 Gas Gauge |
[Y7] Gas_hi (mA) |
[Y8] Gas_hi (in H2O) |
1.163*x-3.488 |
|
|
Virtual Used for DTR |
[Y9] DTR |
[Y10] not used |
100 * max(0, (t-t{FCs})) / (t-t{CHARGE}) |
|
|
Phidget TMP1101 Port 2 Dwyer 605-6 Gas Gauge |
[Y11] Gas-Low (mA) |
[Y12] Gas_low (in H2O) |
0.2*x-0.82 |
|
|
Virtual Display the High Gas |
[Y13] not used |
2* High Gas Graph |
(2*Y7) if (Y7 > 4 ) else (-999) |
|
|
Virtual Display the Low Gas |
[Y15] not used |
[Y16] 2* Low Gas Graph |
2*Y11 |
|
|
Virtual Display Gas Gauge Readings |
Low Gas (in H2O) |
High Gas (in H2O) |
Y11 |
Y7 |
My Setup
- Mill City Roasters 2kg on LP
- Per manual, maximum gas is 14” H2O
- Bean Probe upgraded to 2mm (Mill City sells them)
- Dwyer Magnehelic 605-20 Indicating Pressure Transmitter
- 4” diameter, electronic, 0-20” H2O
- I paid $84.80, including shipping on ebay (new in the box)
- Dwyer Magnehelic 605-3 Indicating Pressure Transmitter
- 4” diameter, electronic, 0-3” H2O
- I paid $75.00, including shipping, on ebay (used)