Spirax Sarco RIM20, Installation And Maintenance Instructions Manual, Page: 110 / 132

IM-P198-05 MI Issue 2 110
6.8 Determine the fault
6.8.1 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 flowrate at no flow.
6.8.2 Symptom: erratic output
1. The flowrate 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. 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 condition
previously described.
2. Mechanical installation may be incorrect. Verify the straight run is adequate as described
in Section 2. 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 Analogue outputs can be smoothed using the
time constant in the Output 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 coefficient Ck may be incorrectly set. The Ck is a value in the equation used to
determine if a frequency represents a valid turbine signal given the fluid density and
signal amplitude. In practice, the Ck value controls the adaptive filter, fi, setting. During
flow, view the f and fi values in the first column of the hidden diagnostics. The fi value
should be approximately 10- 20 % higher than the f value. If you raise the Ck setting
in the Calibration menu, then the fi value will increase. The fi is a low pass filter, so by
increasing it or lowering it, you can alter the range of frequencies that the meter will accept.
If the turbine signal is strong, the fi value will increase to a large number - this is correct.
Fig. 52 Electronics stack sensor connections