Alicat LC Series Liquid Flow Controller - Manual (Page 41)

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Meter does not appear to be accurate when compared against another valid
measurement of the physical flow (such as weight over time).
Water flow meters can normally be compared against one another provided
there are no leaks between the two meters. One common cause of inaccuracy,
inconsistency, or unusual readings is air bubbles trapped in one or both of the
legs of the differential pressure sensor. Bleed the ports as described in this
manual to remove this possibility (See page 11). Another possibility is that the
water has some contaminant or additive, such as antifreeze, that affects the
viscosity of the water. A third possibility is an improper tare error (see page 19).
Controller is slow to react to a set-point change or imparts an oscillation to the flow.
An inappropriate PID tuning can cause these symptoms. Use at conditions
considerably different than those at which the device was originally set up can
necessitate a re-tuning of the PID loop (page 30).
Flow flutters or is jumpy.
The meters are very fast and will pick up any actual flow fluctuations such
as from a diaphragm pump, etc. Also, inspect the inside of the upstream
connection for debris such a Teflon tape shreds. Note: L & LC-Series devices
feature a programmable geometric running average (GRA) that can aid in
allowing a rapidly fluctuating flow to be read. Please see “Pressure Averaging”
and “Flow Averaging” on page 22.
The output signal is lower than the reading at the display.
This can occur if the output signal is measured some distance from the meter
as voltage drops in the wires increase with distance. Using heavier gauge wires,
especially in the ground wire, can reduce this effect.
My controller oscillates wildly and/or exhibits very different reactions to the set-
point than I expect.
Conditions considerably different than those at which the device was originally
set up can necessitate a re-tuning of the PID loop. Avoid long runs of small
diameter tubing in the system, increase line size.
RS-232 / RS-485 Serial Communications is not responding.
Check that your meter is powered and connected properly. Be sure that the port
on the computer to which the meter is connected is active. Confirm that the port
settings are correct per the RS-232 / RS-485 instructions in this manual (Check the
RS-232 / RS-485 communications select screen for current meter readings). Close
HyperTerminal® and reopen it. Reboot your PC. See pages 14, 15 and 32 for more
information on RS-232 / RS-485 signals and communications.
Slower response than specified.
L-Series Meters and LC-Series Controllers feature a programmable Geometric
Running Average (GRA). Depending on the full scale range of the meter, it
may have the GRA set to enhance the stability/readability of the display,
which would result in slower perceived response time. Please see “Pressure
Averaging” and “Flow Averaging” on page 22.