GASMAX/TX Operation & Maintenance Manual, Revision 1.0
Page 12
IMPORTANT:
THE GASMAX/TX INFRARED SENSOR
WILL NOT
DETECT COMBUSTIBLE LEVELS OF
HYDROGEN GAS.
Every six seconds, the GASMAX/TX central processor wakes up, reads the sensor’s digital output, scales
and converts the reading to engineering units, applies correction factors based on the most recent
calibration and displays the value on the LCD display. Based on the gas concentration level and alarm
levels programmed by the user, the microprocessor then determines if a compact wireless data packet
should be broadcast to the site manager or wireless controller / receiver. This data packet includes the
gas value, alarm and fault status bits and battery voltage.
At the conclusion of each “Wakeup Timer” interval, the GASMAX/TX also transmits a larger data packet
containing additional information that includes zero and span values, user-programmed tag and
engineering unit values and communications timeout settings. Third-generation controllers such as the
C2/TX Wireless Site Manager process and display this information, eliminating the need to program both
the gas monitor and site manager or controller.
NOTE:
GDS CORP WIRELESS GAS DETECTORS
CAN ONLY
COMMUNICATE WITH PROPERLY EQUIPPED GDS
CORP CONTROLLERS OR WIRELESS SYSTEM / SITE MANAGERS.
If the GASMAX/TX determines that a data packet should be transmitted, the following events take place:
Power is applied to the radio, the radio is placed in receive mode and listens for the synchronization
beacon transmitted by the site manager or controller / receiver. If the beacon is found, the radio
synchronizes to the beacon hopping pattern, transmits the data packet and returns to sleep mode. This
sequence takes between 250 milliseconds and 1 second to complete. If the radio fails to synchronize with
the beacon, it waits 2 seconds and tries again, then waits 2 seconds and tries once more. If the third
attempt fails an “Out of Range” icon is displayed and the GASMAX/TX goes to sleep until the next six
second interval occurs. The “Out of Range” event will be logged in the Event Log.
FHSS radios for both 900 MHz and 2.4 GHz are available. For North America, 900 MHz is recommended
due to increased power output available (up to 1 watt), greater range and ability of lower frequency
signals to travel around interfering objects. Systems utilizing 2.4 GHz radios transmit at lower power levels
and have corresponding less range. In addition, higher frequency 2.4 GHz signals tend to require a more
direct ‘line of sight’ between the gas detector and controller / receiver antenna. On the other hand, 2.4
GHz systems are generally license-free world-wide and are generally less prone to interference from other
radio frequency sources.
