Laurel Electronics LTE SERIES TRANSMITTERS PULSE INPUT - Manual (Page 27)

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14. INPUT SIGNAL FILTERING
A moving average filter is selectable in software to process the internal digital readings, which
are taken at 60/sec with 60 Hz power and 50/sec with 50 Hz power. Eight settings are selectable
with t equivalent RC time constants from 0.08 sec to 9.6 sec. The longer time constants
provide superior noise filtering at the expense of fast response time.
Adaptive moving average filtering allows the transmitter to respond rapidly to actual changes
in signal while filtering out normal noise. An adaptive filter threshold causes the moving
average filter to be reset to the latest reading when the accumulated difference between
individual readings and the filtered reading exceeds that threshold. The accumulated difference
is also reset to zero when the latest reading has a different polarity than the filtered reading. The
adaptive filter threshold can be selected as low or high. Low is normally selected. High should
be selected if the signal has large transients.
15. TRANSMITTER CALIBRATION
All input ranges are calibrated at the factory using NIST certified calibration equipment, and
the calibration constants are stored digitally in EEPROM on the signal conditioner board. This
allows signal ranges and signal conditioner boards to be changed without recalibration.
Calibration constants for analog outputs are stored in EEPROM on the main board.
If recalibration is required, a transmitter may be returned to the factory or to an authorized
distributor. Easy calibration of DC, AC and load cell signal conditioner ranges is also possible
with Instrument Setup software, as described in Section 7. Advanced calibration software is
available from the factory.
16. CUSTOM CURVE LINEARIZATION
Curve.exe is a DOS-based, executable PC program used to set up an Extended transmitter so
that the internal digital readings have a user-defined, non-linear relationship with the input
signal. For example, it allows a transmitter to correct for transducer nonlinearity. Calculated
linearizing parameters are downloaded from a PC into non-volatile memory of the transmitter.
The curve-fitting algorithm uses quadratic segments of varying length and curvature, and
includes diagnostics to estimate curve fitting errors. The program is self-prompting, avoiding
the need for detailed printed instructions.
To get started, download curve.exe from our website into the directory that will also contain
your data files, such as c:\curves. Connect your transmitter to the PC and double-click on
curve.exe, which is an executable file. Follow the computer prompts and extensive help
information. Pressing R (Enter) returns to the main menu. You will be given the choice of four
data entry modes, which are explained in detail.