Sierra INNOVA-MASS 241-VTP - Manual (Page 61)

Chapter 4 Troubleshooting & Repair Series 24-HP Instruction Manual
4-6 IM-24-HP
Troubleshooting the Flow Meter
Symptom: Output at no Flow
1.
The low flow cutoff is set too low. At no flow, go to the
first column of the hidden diagnostics menu and record the Lvl
value. The low flow cutoff must be set above this value.
2. Example: at no flow , Lvl = 25. Set the low flow cutoff in the
Calibration Menu to approximately 28 and the meter will no
longer read a flow rate at no flow.
Symptom: Erratic Output
1. The flow rate may be too low, just at the cutoff of the meter
range, and the flow cycles above and below the cutoff making
an erratic output. The meter range is stamped on the label on
the outside of the electronics enclosure cover (based on appli-
cation conditions when the meter was ordered). Consult the
factory if necessary to confirm the meter range based on cur-
rent operating conditions. It may be possible to lower the low
flow cutoff to increase the meter range. See the example above
for output at no flow, only this time the low flow cutoff is set
too high. You can lower this value to increase the meter range
as long as you do not create the output at no flow condition
previously described.
2. Mechanical installation may be incorrect. Verify the straight
run is adequate as described in Chapter 2. For in-line meters,
make sure the meter is not installed backwards and there are no
gaskets protruding into the flow stream. For insertion meters,
verify the insertion depth and flow direction.
3. The meter may be reacting to actual changes in the flow
stream. The output can be smoothed using a time constant.
The displayed values can be smoothed using the time constant
in the Display Menu. The analog outputs can be smoothed us-
ing the time constant in the Output Menu. A time constant of 1
will result in the change in value reaching 63% of its final val-
ue in one second. A time constant of 4 is 22%, 10 is 9.5% and
50 is 1.9% of the final value in one second. The time constant
equation is shown below (TC = Time Constant).
4. The
vortex coefficient Ck may be incorrectly set. The Ck is a value
in the equation used to determine if a frequency represents a
valid vortex signal given the fluid density and signal ampli-
tude. In practice, the Ck value controls the adaptive filter, fi,
% change to final value
in one second
= 100 ( 1 – e
(-1/TC) )