Disabling The Display Backlight - GasTech D-Guard2 Operator's Manual

19. APPENDIX B:

19.1. Disabling the Display Backlight

By default, the display backlight is enabled for Group II versions of D-Guard
The backlight LEDs, when enabled create a voltage drop of around 3.0V in the power supply fed to the internal
electronics. For many applications, this is acceptable and no changes are necessary.
For applications where long cable lengths, large barrier resistances and low power supply voltages are present, it may
be required to disable the backlight LEDs to gain additional voltage compliance for the current loop output to function
up to 22mA.
Disabling the LEDs gives around 130 Ohms extra available loop resistance at 22mA, or will allow the supply voltage to
be operated 3.0V lower for a given loop resistance.
Determining whether the backlight link needs to be fitted requires an understanding of the characteristics of the
components of the system into which the detector is installed. If in doubt consult the system designer, plant engineer
or other body with knowledge of the system.
2
and disabled for Group I versions.
Place link here to disable backlight
DO NOT OPEN UP D-GUARD
IN A HAZARDOUS AREA.
WORK ON D-GUARD
BE CARRIED OUT IN A SAFE AREA.
58
2
D-Guard
2
2
MUST ONLY