Sabio 2010D, Operation Manual

Page: 135 / 182

Internal Calibrations Page 8-2
Calibration Data
Two basic types of data may contain the information necessary to
calibrate a device: 2
nd
order polynomial coefficients and/or a
lookup table. This data may then be used to produce equations
characterizing the device using one of four linearization
methods.
Polynomial coefficients are useful for linear or slightly non-
linear devices and are the easiest way to calibrate a device if
the coefficients are already known. The coefficients a, b and c
are used in the following equation to linearize and convert a
voltage signal to engineering units:
Y = a + bX +cX
2
Where:
X = Control or monitor voltage (Volts)
Y = Flow rate or ozone concentration (SCCM or PPB)
a = Intercept
b = Slope
c = Non-linear term
Lookup
tables contain more information and allow more
linearization options. Each table consists of up to 20 rows,
each representing a calibration point, and three columns: the
control voltage, the monitor voltage and the actual flow or ozone
concentration. The data contained in a lookup table may be used
to
automatically calculate polynomial coefficients using
regression techniques or the table’s data may be used directly
for the lookup and spline linearization methods.
Two sets of linearization equations, referred to as the control
and monitor equations, are produced from the calibration data.
The control equation converts the flow or ozone concentration (in
SCCM or PPB, respectively) to a control voltage. The monitor
equation converts a monitored voltage to engineering units for
displaying flow rates or ozone concentrations. Of the two, the
control equations are the most important since they establish the
correspondence between a desired flow rate or ozone concentration
and the control voltage sent to the device. The monitor
equations are only used for scaling measured voltages to
engineering units for presentation on the display.