Noland Engineering RS11 v3.0 Manual page 14

APPENDIX C
Analog Gauge (sensor) Calibration Examples
This Section describes the relatively simple and straightforward method for calibrating analog gauges and sensors so that the
RS11 can output the correct data. To use this method most effectively requires that you have the RS11 installed in the vessel,
CANbus power available, and the engine gauges or sensors operational and connected to RS11 analog inputs (A1-A4). A
voltmeter might also prove useful, but it is not essential since the RS11 analog inputs can function like a voltmeter.
Shown below is an example of an engine oil pressure sensor characteristic. The voltage measured at the "S" (sense) terminal
of the vessels' oil pressure gauge is shown in the graph. It is a negative slope characteristic, which is typical of these sensors.
Most sensors exhibit an approximately linear (straight line) characteristic over their range of interest. The RS11 assumes this
straight line characteristic for all sensors. Two points on the line are needed for each analog gauge or sensor. A voltmeter
may be needed to determine these points, but the RS11 can be used as a voltmeter as described later.
Our first point on the curve is usually easy to obtain. For the case of Oil Pressure, we know the pressure is '0' when the en-
gine is not running, so all we need is the gauge voltage with engine 'off' but gauges switched 'on'. That reading is repre-
sented by the upper left point (8.4V) on the example graph above. Rather than use a voltmeter, we could instead read the "%
f.s" volts measurement from the "$PNOLA,... " sentence of the RS11 (see Section 4– Output Data Monitoring). If A1 is
assigned to "Oil pressure" and the full-scale jumper setting in the RS11 is set to 10V, the reading would show
"$PNOLA,84.0, .." for the Oil Pressure analog input (A1 shown here). Note that 10V x 84% = 8.4V, so in effect we are using
the RS11 analog input as a voltmeter.
Next, with the engine running, assume the oil pressure increases to 66 psi and the gauge voltage now reads "2.7V" (or
"$PNOLA,27.0,.."). This is our second data point for calibrating this gauge/sensor. The other three gauges/sensors are cali-
brated the same way. The recorded data points for all gauges or sensors are then entered in to the Setup Utility, which will
process and download calibration factors to the RS11.