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DAT420_MAN02_EN.docx • V1R1
8
DAT 420
6.2
CALIBRATION FOR TOXIC GASES
NO
2
: for DAT 420 detectors fitted with a 0-20 ppm or 0-50 ppm nitrogen dioxide sensor,
use a calibration gas composed of NO
2
at 20 ppm in air!
1.
During adjustment, avoid touching the transmitter circuit or its components with your fingers.
2.
Allow the detector to be powered for at least 24 hours beforehand.
3.
Position the calibration mask and connect the cylinder of nitrogen, the flowmeter and the voltmeter as
shown above.
4.
Adjust the flow rate to between 0.4 and 0.6 l/min and apply nitrogen until the voltmeter display has
stabilised (min. 2 to 3 minutes).
5.
On the transmitter, adjust the "
ZERO
" potentiometer (figure below) to obtain
40 mV ± 0.1 mV
on the
voltmeter.
Figure 7 : Calibration for toxic gases
6.
Stop applying nitrogen and wait until the 40…200 mV output signal is completely stable.
7.
Replace the nitrogen cylinder with the cylinder of calibration gas and apply gas at a rate suitable for
the type of gas being used (see Table 2 - page 11). Wait until the voltmeter reading is completely
stable (see "Exposure" in Table 2 - page 11).
8.
Adjust the "GAIN" potentiometer (figure above) to obtain a reading on the voltmeter corresponding to
the ratio between the calibration gas and the target measuring range.
This value is given, in mV, by the following formula :
10
4
4
20
×
+
−
×
=
Range
Gas
CAL
Measure
V
CY
REGULATOR
VOLTMETER
mV
═
+
-
+
-
"GAIN"
POTENTIOMETER
"ZERO"
POTENTIOMETER
V
Measure
.
ZERO
GAIN
