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Analogue signal
— A current between 4 and 20 mA flows through the current loop during normal op-
eration. This current is proportional to the gas concentration.
— The Polytron 7500 uses various current values to indicate the operating status:
Current
4 mA
20 mA
<3.2 mA
3.8 mA ... 4 mA
20 mA ... 20.5 mA
>21 mA
3.4 mA
1)
<3.2 mA
for 1 second
every 10 seconds1)
1)
Factory setting; can be configured as desired, page 52.
Display
— In measuring mode, the display shows the actual gas concentration, e.g.:
An alarm is triggered:
— when the alarm threshold for the concentration alarm is exceeded,
— if the measured concentration exceeds the full-scale value:
Y Y Y Y
the special symbol »
— If the measured concentration drops below the calibrated zero point:
X X X X
the special symbol »
9023927 - 2nd edition - May 2007
Meaning
Zero point
Full-scale value
Fault
Sensor drift below zero point
Measuring range exceeded
Fault in analogue output
Maintenance signal
1)
Warning signal
(factory setting: off)
« is then displayed instead of the measured value.
« is then displayed instead of the measured value.
0.9
NF
ppm
3
5.0
NF
A1
3
Y Y Y Y
NF
ppm
3
X X X X
NF
ppm
3
Page 17 of 72 Pages
Start-up
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