Emerson Rosemount 8732EM, Reference Manual

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10.5.2 Auto zero
LOI menu path Diagnostics > Trims > Auto Zero
To ensure optimum accuracy when using 37 Hz coil drive mode, there is an auto zero
function that should be initiated. When using 37 Hz coil drive mode it is important to zero
the system for the specific application and installation.
The auto zero procedure 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.
• With the transmitter in 37 Hz coil drive mode. Never attempt this procedure with
the transmitter in 5 Hz coil drive mode.
• 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 procedure. The transmitter
completes the procedure automatically in about 90 seconds. A clock symbol will appear in
the lower right-hand corner of the display to indicate that the procedure is running.
Note
Failure to complete an auto zero may result in a flow velocity error of 5 to10% at1 ft/s (0.3 m/s).
While the output level will be offset by the error, the repeatability will not be affected.
10.5.3 Digital signal processing (DSP)
LOI menu path Detailed Setup > Signal Processing
The transmitter contains several advanced functions that can be used to stabilize erratic
outputs caused by process noise. The signal processing menu contains this functionality. If
the 37 Hz coil drive frequency has been set, and the output is still unstable, the damping
and signal processing function should be used. It is important to set the coil drive
frequency to 37 Hz to increase the flow sampling rate. The transmitter provides an easy
and straightforward start-up, and also incorporates the capability to deal with difficult
applications that have previously manifested themselves in a noisy output signal. In
addition to selecting a higher coil drive frequency (37 Hz vs. 5 Hz) to isolate the flow signal
from the process noise, the microprocessor can scrutinize each input based on three user-
defined parameters to reject the noise specific to the application.
Operating mode
LOI menu path Detailed Setup > Signal Processing > Operating Mode
Digital Signal Processing
136 Rosemount ® 8732EM Transmitter with HART Protocol Reference Manual