26
TROUBLESHOOTING
Display does not come on or is weak.
Check power and ground connections.
Flow reading is approximately fi xed either near zero or near full scale regardless of actual
line fl ow.
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 fl ow, volumetric fl ow, pressure or temperature is fl ashing and message MOV,
VOV, POV or TOV is displayed:
Our fl ow 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 fl ashes on the display, neither the
fl ashing parameter nor the mass fl ow measurement is accurate. Reducing the value of the fl ashing
parameter to within specifi ed limits will return the unit to normal operation and accuracy.
Meter reads negative fl ow when there is a confi rmed no fl ow condition.
This is an indication of an improper tare. If the meter is tared while there is fl ow, that fl ow is accepted
as zero fl ow. When an actual zero fl ow condition exists, the meter will read a negative fl ow. Simply re-
tare at the confi rmed zero fl ow condition. Also note that while the meter is intended for positive fl ow, it
will read negative fl ow with reasonable accuracy, but not to the full scale fl ow rate (it is not calibrated
for bi-directional fl ow) 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 fl ow meters should not be compared to mass fl ow meters. Mass fl ow
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 fl ow 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 specifi ed set of standard conditions. The calibration sheet provided with each meter lists
its standard conditions.
Flow fl utters or is jumpy.
The meters are very fast and will pick up any actual fl ow fl uctuations such as from a diaphragm pump,
etc. Also, inspect the inside of the upstream connection for debris such a Tefl on tape shreds.
Note: M Series meters feature a programmable geometric running average (GRA) that can aid in
allowing a rapidly fl uctuating fl ow to be read (see “Pressure Averaging” and “Flow Averaging” page
15).
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 or 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. Confi rm that the port settings are correct per the RS-232 or
RS-485 instructions in this manual (Check the RS-232 or RS-485 communications select screen for
current meter readings). Close HyperTerminal® and reopen it. Reboot your PC.
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