Alicat M Series Mass Flow Meter - Manual (Page 32)

32
TROUBLESHOOTING
Display does not come on or is weak.
Check power and ground connections. Please reference the technical
specifications (pages 41-56) 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. Avoid installations that can
subject the sensor to excessive pressure differentials (see page 7). 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 meter 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.
Meter reads negative flow when there is a confirmed no flow condition.
This is an indication of an improper tare. If the meter is tared while there is flow,
that flow is accepted as zero flow. When an actual zero flow condition exists,
the meter will read a negative flow. Simply re-tare at the confirmed zero flow
condition. Also note that while the meter is intended for positive flow, it will
read negative flow with reasonable accuracy, but not to the full scale flow rate
(it is not calibrated for bi-directional flow) and no damage will result.
Meter does not agree with another meter I have in line.
Volumetric meters are affected by pressure drops. Volumetric flow meters
should not be compared to mass flow meters. Mass flow meters can be
compared against one another provided there are no leaks between the two
meters and they are set to the same standard temperature and pressure. Both
meters must also be calibrated (or set) for the gas being measured. M-Series
mass flow meters are normally set to Standard Temperature and Pressure
conditions of 25° C and 14.696 psia. Note: it is possible to special order meters
with a customer specified set of standard conditions. The calibration sheet
provided with each meter lists its standard conditions.
When performing this comparison it is best to use the smallest transition
possible between the two devices. Using small transitions will minimize lag and
dead volume.