Emerson Rosemount 8782 Reference Manual page 109

Reference Manual
00809-0100-8782
10.4.2 Auto zero
LOI menu path
To ensure optimum accuracy at either low or high frequency, there is an auto zero trim
that should be initiated. This is more important at High frequency or if running at low flow
rates (<0.3 m/s).
The auto zero trim should be performed only under the following conditions:
• With the transmitter and sensor installed in their final positions. This procedure is not
applicable on the bench.
• The coil drive frequency can be either Low or High. The auto zero trim will calculate
both Low and High frequency auto zero offsets.
• With the sensor full of process fluid at zero flow.
These conditions should cause an output equivalent to zero flow. Set the loop to manual if
necessary and begin the auto zero trim. The transmitter completes the auto zero trim
automatically in about 90 seconds. A clock symbol will appear in the lower right-hand
corner of the display to indicate that it is running.
Note
Failure to complete an auto zero trim may result in a flow velocity offset error of 0 to 2% at
1 ft/s (0.3 m/s) at Low frequency and 5% to 10% at 1 ft/s (0.3 m/s) at High frequencies.
While the output level will be offset by the error, the repeatability will not be affected.
10.4.3 Other signal processing tools
The transmitter contains several advanced functions that can be used to stabilize erratic
flow readings caused by process noise. If the High coil drive frequency has been set, and
the flow reading is still unstable, the damping and signal processing functions should be
adjusted. It is best to set the coil drive frequency to High to increase the flow sampling
rate. In addition to selecting a higher coil drive frequency (High vs. Low) to isolate the flow
signal from the process noise, the transmitter can measure the noise level and
automatically adjust and analyze each input based on user defined parameters to reject
the noise specific to the application.
Signal processing mode
LOI menu path
The signal processing mode is the primary way the user should adjust the signal
processing. The signal processing modes in
processing settings.
Table 10-1: Signal processing modes
Signal processing mode
Off
Minimal
Reference Manual
Diagnostics → Trims → Auto Zero
Detailed Setup → Signal Processing → SP Mode
Table 10-1 automatically configure the signal
Description
Signal processing is disabled.
Provides a minimal amount of signal processing
to remove spike noise with the fastest response.
Digital Signal Processing
November 2019
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