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Description
The GDS 404 is a multi channel combustible and toxic gas monitor, which can accommodate up
to 4 sensor channels housed in wall mounting enclosure. Sensors may be added or removed as
required, but should be carried out with the power to the unit switched off. Each sensor continuously
monitors for gas, with the digital display sequentially sampling each sensor reading. Where a
particular sensor reading requires to be viewed, the hold button should be pressed when the
channel indicator is on the appropriate sensor, pressing the hold button again will restart the
sampling sequence.
The gas alarms are activated at preset levels and will remain on until the gas clears, these in turn
activate the appropriate alarm relays. The fault indicator is initiated should the sensor connecting
lines become open/short circuit, or an electronic fault be detected.
The control unit requires an a.c. mains power supply and/or a low voltage d.c. power supply.
When both are provided the low voltage d.c. acts as a standby supply in the event of an a.c. mains
power failure.
HOLD
(Fig.1) Pressing and releasing the button will hold the meter display on a particular sensor
channel which is indicated by the amber L.E.D., press again to continue the auto step sequence.
RANGE INDICATORS
Three range indicators are positioned directly above the panel meter %L.E.L.
(Lower Explosive Level), PPM (Parts Per Million) and %Volume, each sensor is addressed to indicate
its appropriate range.
MAINS ON LAMP
(P) GREEN indicates that power is being supplied to the control unit.
When the optional standby battery is fitted loss of mains supply will result in the GREEN Mains ON
Lamp changing to RED.
ALARM LAMPS
C1, C2, C3, C4 - Lo and Hi RED illuminated when the gas concentration increases
beyond the alarm trip points.
FAULT LAMP
(F) AMBER illuminated in the event of a sensor cable fault or sensor supply circuit /
electronic fault or DC output / fuse fault.
SOUNDER
initiated in the presence of a fault or gas alarm condition.
TEST
When pressed for 15 seconds alarm L.E.D’S are activated. If pressed for a further 15 seconds
alarm relays will change state.
RESET
used to mute the sounder and reset alarms, gas alarms cannot be reset until the gas
concentration has decreased below the set alarm level.
ALARM RELAY INHIBIT
Pressing the reset pad for 15 seconds will inhibit the alarm relays which is
indicated by the fault light coming on. To remove the inhibit press the reset pad for 15 seconds, the
fault light will turn off.
ZERO POTENTIOMETER
meter zero adjust when the sensor is monitoring a gas free atmosphere.
SPAN POTENTIOMETER
used to adjust the meter indication to read correctly when the sensor is
subject to a test gas of known concentration.
ALARM SET SWITCH
alarm trip points setting.
SENSOR CURRENT POTENTIOMETER
sensor supply adjustment.
