Alicat PCU Portable Calibration Unit - Manual (Page 24)

24
TROUBLESHOOTING
Display does not come on or is weak.
Recharge the battery.
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 sensor to pressure
drops in excess of 10 PSID. A common cause of this problem is instantaneous application of high-
pressure gas as from a snap acting solenoid valve upstream of the meter. Damage due to excessive
pressure differential is not covered by warranty.
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.
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 (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 will often not agree with one another when put in series because they 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. PCU 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.
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: PCU
meters feature a programmable geometric running average (GRA) that can aid in allowing a rapidly
fluctuating flow to be read.
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.
RS-232 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 instructions
in this manual (Check the RS-232 communications select screen for current meter readings). Close
HyperTerminal® and reopen it. Reboot your PC.