Reference Manual
00809-0100-4004, Rev BA
August 2010
4-17
Rosemount 8800D
Primary Variable (PV)
PV is the actual measured variable. On the bench, the PV value should be
zero when the PV is mapped to a flow variable. Check the units on the PV to
make sure they are configured correctly. See PV Units if the units format is not
correct. Use the Process Variable Units function to select the units for your
application.
Signal/Trigger Level Ratio (Sig/Tr)
The Signal to Trigger Level Ratio is a variable that indicates the flow signal
strength to trigger level ratio. This ratio indicates if there is enough flow signal
strength for the meter to work properly. For accurate flow measurement, the
ratio should be greater than 4:1. Values greater that 4:1 will allow increased
filtering for noisy applications. For ratios greater than 4:1, with sufficient
density, the Optimize Flow Range function can be utilized to optimize the
measurable range of the flowmeter.
Ratios less than 4:1 may indicate applications with very low densities and/or
applications with excessive filtering.
Low Flow Cutoff
Low Flow Cutoff enables you to adjust the filter for noise at no flow. It is set
at the factory to handle most applications, but certain applications may require
adjustment either to expand measurability or to reduce noise.
The Low Flow Cutoff offers two modes for adjustment:
• Increase Range
• Decrease No Flow Noise
It also includes a dead band such that once flow goes below the cutoff value,
output does not return to the normal flow range until flow goes above the dead
band. The dead band extends to approximately 20 percent above the low flow
cutoff value. The dead band prevents the output from bouncing between 4mA
and normal flow range if the flow rate is near the low flow cutoff value.
Low Pass Filter
The Low Pass Filter sets the low-pass filter corner frequency to minimize the
effects of high frequency noise. It is factory set based
on line size and service type. Adjustments may be required only if
you are experiencing problems. See Section 5: Troubleshooting.
The Low Pass Filter corner frequency variable offers two modes for
adjustment:
• Increase filtering
• Increase sensitivity
Field Comm. 1, 4, 3, 2, 1
Field Comm. 1, 4, 3, 2, 2
Field Comm. 1, 4, 3, 2, 3
Field Comm. 1, 4, 3, 2, 4
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