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Reference Manual
00809-0100-4860, Rev BC
Section 4: Operation
January 2013
Operation
Manual filter adjust
Manual Filter Adjust allows you to manually adjust the following settings: Low Flow Cutoff, Low
Pass Filter, and Trigger Level, while monitoring flow and or sig/tr.
Primary Variable (PV)
PV is the actual measured 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.
Field Comm. 1, 4, 3, 2
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