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Technical Support
PS-3204
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013-14662B
15.
Click
Next
.
16.
Click
Finish
. Rinse and dry the probe before using it
for data measurement.
Theory of Calibration
One of the functions of the PASCO Data Collection
Software is to take the stream of raw data from a sensor
and transform it into the calibrated data that you see in the
Graph, Table, and other displays. If you do not calibrate a
sensor yourself, the software uses a default calibration that
is loaded when the sensor is connected.
You can think of the software as taking in raw data and
outputing calibrated data. When you perform a calibration,
the software redefines the linear equation that transforms
the raw input data into the calibrated output data. The linear
function is of the form:
Raw Input = Slope x Calibrated Offset
Or:
Calibrated Output = (Raw Input - Offset)/Slope
The function can be represented graphically as a line.
Two points, Pt 1 and Pt 2, define the line. In the two-point
calibration procedure, each point is reset by associating a
known standard value (for instance, the pH of a buffer
solution) with a raw input measurement that the sensor
sends to the GLX when it is in that standard. In a one-point
calibration, only one of the points is reset by the user.
Types of Calibration
There are three types of calibration: two-point, one-point
slope, and one-point offset. Any of these calibrations can
be performed on a single sensor, or simultaneously on
multiple similar sensors; however, for any given sensor, the
software will automatically select the most typical
calibration type as the default setting.
Two-Point
In a two-point calibration, you reset two points to define a
new line. This type of calibration affects both the slope and
the offset.
One-Point Slope
In a one-point slope calibration, you reset only one point.
The slope of the line changes so that the line intersects the
new point, while the offset (or Y-intercept) does not change.
One-Point Offset
In a one-point offset calibration, you reset only one point.
The line shifts so that it intersects the new point, but its
slope does not change.
Offset calibration is usually used to make one sensor agree
with another sensor. Due to normal variation among
probes, a second probe might read consistently higher than
the first probe. Normally this difference would be
insignificant; however, an offset calibration can be used to
bring the sensors into closer alignment.
