Aalborg DFM Digital - Manual (Page 51)

47
NO. INDICATION LIKELY REASON SOLUTION
1 No zero reading after
15 min. warm up time
and no flow condition. Embedded temperature
has been changed. Perform Auto Zero Procedure (see section
5.3.10 "Zero Calibration").
2 LCD Display remains
blank when unit is
powered up. No
response when flow is
introduced from analog
outputs 0-5 Vdc or
4-20 mA. Power supply is bad or
polarity is reversed. For 12 or 24 Vdc option:
Measure voltage on pins 1 and 18 of the 25
pin D-connector. If voltage is out of
specified range, then replace power supply
with a new one. If polarity is reversed
(reading is negative) make correct
connection.
For ±15Vdc option:
Measure voltage on pins 1-18 and 14-18
of the 25 pin D-connector. If voltage is out
of specified range, then replace power
supply with a new one. If polarity is
reversed (reading is negative) make correct
connection.
PC board is defective. Return DFM to factory for repair.
3 LCD Display reading or
/and analog output
0-5Vdc signal fluctuate
in wide range during
flow measurement. Output 0-5 Vdc signal
(pins 2-15, 3-16, 4-17
of the D-connector) is
shorted on the GND or
overloaded. Check external connections to pins 2-15,
3-16, 4-17 of the D-connector. Make sure
the load resistance is more than 1000 Ohm.
4 LCD Display reading
does correspond to the
correct flow range, but
0-5 Vdc output signal
does not change
(always the same read
-ing or around zero). Output 0-5Vdc
schematic is burned
out or damaged. Return DFM to factory for repair.
Analog flow output
scale and offset
variable are corrupted. Restore original EEPROM scale and offset
variable or perform analog output
recalibration (see section 7.3).
5 LCD Display reading
and 0-5 Vdc output volt
age do correspond to
the correct flow range,
but 4-20 mA output
signal does not change
(always the same or
reading around 4.0 mA). External loop resistance
is open or more than
500 Ohm. Check external connections to pins 2 and
15 of the D-connector. Make sure the loop
resistance is less than 500 Ohm.
Output 4-20 mA
schematic is burned
out or damaged. Return DFM to factory for repair.
6 Calibration is off (more
than 1.0 % F.S.). DFM has initial zero
shift. Shut off the flow of gas into the DFM
(ensure gas source is disconnected and no
seepage or leak occurs into the meter).
Wait for 15 min. with no flow condition and
perform Auto Zero calibration Procedure
(see section 5.3.10 "Zero Calibration").
7 LCD Display reading is
above maximum flow
range and output
voltage 0-5 Vdc signal
is more than 5.0 Vdc
when gas flows
through the DFM. Sensor under
swamping conditions
(flow is more than 10%
above maximum flow
rate for particular
DFM). Lower the flow through DFM within
calibrated range or shut down the flow
completely. The swamping condition will
end automatically.
PC board is defective. Return DFM to factory for repair.