Xylem H-4271 - Manual (Page 9)

The H-4191 has an internal inactivity timer which keeps the module awake to process the service
request and receive subsequent packets from the radio. If both the RS-232 and SDI-12 ports
become inactive (and both CTS and RTS are not asserted) for longer than 10-seconds, the timer
expires and the H-4191 enters its low power sleep mode. The H-4191 examines the
“aTTTN” sensor response initiated by an “aM!” measure command and initializes a
second “keep-awake” timer to TTT + 3-seconds. This ensures the H-4191 will remain awake to
process the service request. When the service request actually arrives, the keep-awake timer is
zeroed. While the keep-awake timer is running the H-4191 sends a null (00h) to the radio
once/second to keep the radio link awake while waiting for the service request. The data logger
must discard the 00h characters.
When using a H-4191 SDI-12 gateway, the data logger must prefix all messages with four or five
0xFF characters to allow the H-4191 to awaken before the message payload arrives. The H-4191
automatically discards 0xFF characters such that they are not passed on to the SDI-12 sensor.
The radios used in this architecture are normally programmed for “sleep & sniff” low power
operation. When properly configured, the data logger, radios and H-4191 module can provide a
low-power wireless SDI-12 bridge capable of performing retries.
1.11 FCC Restrictions
This equipment has been tested and found to comply with the limits for a Class B digital device,
pursuant to Part 15 of the FCC Rules. These limits are designed to provide reasonable protection
against harmful interference in a residential installation. This equipment generates, uses, and can
radiate radio frequency energy and, if not installed and used in accordance with the instructions,
may cause harmful interference to radio communications. However, there is no guarantee that
interference will not occur in a particular installation. If this equipment does cause harmful
interference to radio or television reception, which can be determined by turning the equipment
off and on, the user is encouraged to try to correct the interference by one or more of the
following measures:
! Reorient or relocate the receiving antenna.
! Increase the separation between the equipment and receiver.
! Connect the equipment into an outlet on a circuit different from that to which the receiver is
connected.
! Consult the dealer or an experienced radio/TV technician for help
1.12 Agency Certifications
The 9Xtend RF module complies with Part 15 of the FCC rules and regulations. Compliance
with the labeling requirements, FCC notices and antenna usage guidelines is required by the
system integrator. The 9XTend module may only be used with antennas that have been tested an
approved for use with this module.
H-4271
Introduction 1-5