Alicat MC Series Mass Flow Controller - Manual (Page 40)

40
TROUBLESHOOTING
Display does not come on or is weak.
Check power and ground connections. Please reference the technical specifications
(pages 50 - 70) to assure you have the proper power for your model.
Flow reading is approximately fixed either near zero or near full scale
regardless of actual line flow.
Differential pressure sensor may be damaged. A common cause of this problem
is instantaneous application of high-pressure gas as from a snap acting solenoid
valve upstream of the meter. If you suspect that your pressure sensor is
damaged please discontinue use of the controller and contact Alicat.
Displayed mass flow, volumetric flow, pressure or temperature is flashing and
message MOV, VOV, POV or TOV is displayed:
Our flow meters and controllers display an error message (MOV = mass
overrange, VOV = volumetric overrange, POV = pressure overrange, TOV =
temperature overrange) when a measured parameter exceeds the range of the
sensors in the device. When any item flashes on the display, neither the flashing
parameter nor the mass flow measurement is accurate. Reducing the value of
the flashing parameter to within specified limits will return the unit to normal
operation and accuracy. If the unit does not return to normal contact Alicat.
After installation, there is no flow.
Alicat MC controllers incorporate normally closed valves and require a set-point
to operate. Check that your set-point signal is present and supplied to the correct
pin and that the correct set-point source is selected under the SETPT SOURCE list
in the control set up display. Also check that the unit is properly grounded.
The flow lags below the set-point.
Be sure there is enough pressure available to make the desired flow rate. If
either the set-point signal line and/or the output signal line is relatively long, it
may be necessary to provide heavier wires (especially ground wiring) to negate
voltage drops due to line wire length. An inappropriate PID tuning can also
cause this symptom if the D term is too large relative to the P term. See pages
20 and 21 for more information on PID tuning.
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. See pages 20 and 21 for more
information on PID tuning.
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.