Connection to other central devices 1
Colour code of connecting terminals and/or leads at the gas sensor:
Connected values:
For field operation, we recommend to supply a constant current between 200 and 400 mA DC to the gas sensor.
Alternatively, the gas sensor can be operated with a constant voltage between 2 and 5 V DC. Then, the cable length amounts to max. 5 m.
This operating mode is intended for settings at service centres.
Power consumption amounts to max. 1 W for both operating modes.
The gas sensor automatically detects a constant current supply or a constant power supply when the central device is switched on.
The leads between central device and gas sensor must have a sufficiently low resistance to ensure the correct supply voltage at the gas sen-
sor. For constant current mode, the maximum resistance per core is calculated as follows:
Example:
With I
C
= 200 mA, P
C
= 1.6 W, the result is a maximum resistance per core of R = 7.5 ¾.
With cable lengths per core of 1500 m, the resistance per unit length R’ = 50 ¾ / 1500 m = 33 ¾/km may not be exceeded.
In constant voltage mode, unequal lead resistances can lead to a deviation between the output signal of the gas sensor and the gas concen-
tration displayed by the central device as well as to a periodic fluctuation of the output signal. In this case, sensor signal and central device dis-
play must be alined as described in the Instructions for Use under "display target gas category". Common central devices are equipped with
standard low-pass filters (with a typical time constant of 10 seconds) which usually smoothen the periodic fluctuations of output signals.
Commissioning of the System
The DrägerSensor IR infrared gas sensor is preconfigured and ready for use after installation.
z
To avoid false alarms, the alarm call to the central device is to be deactivated.
z
When the supply voltage is applied, the gas sensor automatically performs a self check (10 seconds). Then it uses the calibration (see
Instructions for Use) and target gas category set for delivery.
For the duration of the self test, the gas sensor issues a signal of approx. –15 %LEL. (Remark: When gas sensor and central device are
not trimmed, the value indicated at the central device might deviate).
z
Wait for the running-in period of one minute to expire. No settings can be changed at the gas sensor during this phase. For the duration of
the running-in period, the gas sensor issues a signal of approx. –15 %LEL.
z
Check signal transmission and adjust if required (see Instructions for Use "Checking the signal transmission", "Checking the alarm trigger"
and "Displaying the target gas category".
z
Check setting of the target gas category for the intended use. Set target gas category if required (see Instructions for Use "Changing the
target gas category").
z
Check the calibration of the gas warning system (see Instructions for Use "Calibration").
z
Reactivate the alarm call to put the system back to normal operating state.
1
The measuring function for the explosion protection according to EN 61779 is not proven.
Terminal 1 (brown)
=
+ (supply)
Terminal 2 (yellow)
=
output signal (concentration-dependent medium potential of the half bridge)
Terminal 3 (black)
=
– (common reference potential)
P
C
– 1 W
R =
___________
2 x I
C
2
with
R:
maximum resistance per core
I
C
:
constant current set at central device
P
C
:
Performance of the central device with I
C
(according to manufacturer's instructions)
NOTICE
Cable resistance deviations caused by temperature influences, transition resistances of terminals, etc. can also contribute to the fact that the
calculated cable length can not be fully used.
To keep cable losses to a minimum, we recommend setting the constant current as low as possible at the central device.
NOTICE
To prevent moisture condensation on the optic surfaces of the device, parts of the transmitter housing are heated from the inside. This can
increase the surface temperature by approx. 5
o
C.