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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.

  1. 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. 
  2. 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.
    1. 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
    2. 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)
  3. Mine expressions worked out to be:
Dwyer 605-6 (0-3” H20):  (0.2)*Y11+(-0.82)
Dwyer 605-20 (0-20” H20):  (1.163)*Y7+(-3.488)
The Device Assignment in Artisan Scope is:
My variable Assignments in Artisan are:


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)
When gas pressure is greater than 3”, the 205-6 gauge will simply be at maximum and the 605-20 will be used. As the gas is lowered below 3”, the 605-3 will become usable. The 605-20 can continue to send data to the Phidget, but is harder to read at low numbers.  Note that above 3.0, the 605-3 may result in Artisan reading an error and displaying “-1”.

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