Sierra INNOVA-FLO 220 - Manual (Page 55)

Chapter 5 Troubleshooting & Repair Series 220/221 Instruction Manual
agnostics) and then actuate the enter key twice. This action will cause the
meter to output its 4 mA or 20 mA condition. If the DVM indicates a
current greater than ± 0.006 mA from 4 or 20, adjust the setting up or
down until the output is calibrated. Note: these settings are not for adjust-
ing the output zero and span to match a flow range, that function is lo-
cated in the Output Menu.
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 Lvl value. The low flow
cutoff must be set above this value.
Example: at no flow, Lvl = 25. Set the low flow cutoff in the Cali-
bration 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 application conditions when
the meter was ordered). Consult the factory if necessary to confirm
the meter range based on current 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 condi-
tion 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 protrud-
ing 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 using the time constant in the Out-
put Menu. A time constant of 1 will result in the change in value
reaching 63% of its final value 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).
% change to final value
in one second
= 100 ( 1 – e
(-1/TC) )
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 amplitude. In prac-
5-4 IM-22