Drew Technologies DashDAQ XL, Instruction Manual, Page: 31 / 52

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Figure 28: Parameters for Economy Calculator
This calculator uses airflow to find the amount of fuel entering the motor. Vehicles with a Mass Airflow Sensor can measure airflow
directly. In this case you’d only need to configure four parameters:
•
Air Fuel Ratio:
14.7 for gasoline
•
Fuel Density:
720 for gasoline
•
Speed Signal: Vehicle Speed from GenericOBD2
•
Mass Air Flow Signal: Air Flow Rate from MAF from GenericOBD2
If the vehicle does not have a Mass Airflow sensor, this driver provides a way to estimate MAF based on Manifold Absolute Pressure and
a few other variables. In this case you’d additionally need to set:
•
Mass Air Flow Signal: Calculated Mass Airflow from Economy Calculator
•
Intake Air Temperature: Intake Air Temperature from GenericOBD2
•
Manifold Pressure: Manifold Absolute Pressure from GenericOBD2
•
Engine Displacement: Based on the motor, in liters. For example, 2.7 for some Dodge Chargers
•
Volumetric Efficiency:
Based on the motor. For example, enter 0.67 for 67% efficiency.
Once configured this driver provides two signals that you may assign to any gauge (section 0):
•
Fuel Economy vs Distance: Shows MPG or km/L depending on the Imperial/Metric setting
•
Fuel Economy vs Time: Shows gallons/hour or L/hour depending on the Imperial/Metric setting
If you’ve assigned a statistic to a gauge but you’re not seeing values, double-check that you’ve assigned signals for each parameter. Also
try assigning each input signal to a gauge to verify that the DashDAQ is actually able to get a reading.
Rescale Signal Calculator
DashDAQ can perform a multiplier/offset calculation. This can be used to rescale a signal, for example adjusting the vehicle speed to
compensate for tire size. Alternately this could be used to compare two signals, for example subtracting manifold absolute pressure
from atmospheric pressure to find turbocharger boost pressure.
The calculator implements a simple, linear scaling:
Output Signal = (Multiplier Signal) * Input Offset Signal
This provides the ultimate in flexibility because you can multiply two signals together, add/subtract two signals, multiply a signal by a
constant value, etc.
Make sure that the “Rescale Signal Calculator” was selected when reflashing the firmware (section 0) and install the driver on an
available port (section 0). This calculator can be installed several times; once for each signal that you wish to rescale. There are a few
critical parameters:
•
Input Signal:
Signal to modify. Pick a signal for vehicle speed, voltage, or anything you want to rescale.
•
Multiplier Signal: Either a vehicle signal or “Constant Multiplier” described below
•
Multiplier Sign : Specify 1 to leave the multiplier unchanged, or -1 to make the multiplier negative
•
Offset Signal: Either a vehicle signal or “Constant Offset” described below
•
Offset Sign : Specify 1 to leave the offset unchanged (add), or -1 to make the offset negative (subtract)