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1/99 SMV 3000 Transmitter User’s Manual 117
10.5 Resetting Calibration
About Reset Accuracy
for PV1 and PV2
You can erase incorrect PV1 and/or PV2 calibration data by resetting the
data to default values. The default values return the transmitter calibration
to the original factory “characterization” values for the existing LRV and
URV. Characterization calculates a mathematical model of the
performance of the transmitter’s sensors and then stores that data in the
transmitter’s memory. Note that this is not the “final calibration” which is
done at the end of the process against the ordered range.
While resetting the calibration will return the transmitter to a close
approximation of the previous calibration using its stored characterization
data, the accuracy of the “reset” transmitter will be lower than the
specified final calibrated accuracy. The calibration is not exact since the
transmitter mounting angle may be different than the factory mounting
angle and time drift may have occurred since the factory characterization.
This means that the transmitter is calculating its output based on the
characterization equation alone without any compensation for the small
residual errors of zero offset and span correction.
For example, a typical zero offset correction is less than 0.1 inH
2
O for a
400 inH
2
O range and a typical span correction is less than 0.2% regardless
of the range (down to the point where specification turndown begins). The
typical performance of a 400 inH
2
O transmitter after a calibration reset (or
a “Corrects Reset” as it is often called) can be expressed as:
Accuracy = 0.2% +
OinH Span
OinH 0.1
2
2
• 100%
By correcting the zero input, the typical performance will be 0.2% or
better.
For other transmitter ranges, the initial zero offset will be scaled by the
ratio of the Upper Range Limit (URL) to 400 inH
2
O at 39.2 °F (4 °C).
Thus, for a 100 psi range, the initial zero offset can be expressed by:
psi 0.025or O inH 0.7
OinH 400
OinH 2768
O inH
2
2
2
2
=•1.0
Note that these are typical values and they may vary. However, our
patented characterization method includes several techniques that help to
ensure that this level of performance can be achieved.
Continued on next page