Xylem H-4400 - Manual (Page 3)

Chapter 1
Introduction
H-4400
RS-232 Data Radio 1-1
1.0 Introduction
The W ATER LOG ® H-4400 is a spread spectrum RS-232 radio bridge. The H-4400 radio link is
often used to interface a data recorder with a remote “point-of-sale” display. The display allows
water level data to be displayed at a project office or other location remote from the data recorder
and water level sensing equipment.
The radio link uses modern direct sequence spread spectrum telemetry radios. Spread spectrum
technology is highly secure and has good interference immunity. The radio operates in the
license-free 900 Mhz ISM Band.
Two or more H-4400 modules are required; one connected to the data recorder (master) and one
or more located at the remote (slave) sites. The master and slave H-4400 modules are identical.
Normally the RS-232 data transfer is unidirectional - master to slave only. No device addresses
or setup is required, the master broadcasts to all slaves at the same time.
The radio internal to the H-4400 has a built-in electronic switch with controls power to the radio.
A push-on jumper on the radio selects either full power or power-save operation. When the
jumper is set to “Always On” the radio is powered continuously and draws approximately 60mA
continuous. When the jumper is set to “External (DTR)” the power is controlled by the RS-232
DSR input signal (pin-4).
1.1 Operation
The H-4400 operates as a transparent 9600-baud RS–232 radio bridge. No programming or
special setup is needed. The radio in the slave station(s) must be jumpered for “Always On”. All
slave sites must be powered continuously or they will miss the data transmissions. The radio in the
master station can be jumpered for either “Always On” or “External (DTR)” depending on your
application. If the master station is connected to a data logger, the External DTR control setting
should be used to save power. If the external power control mode is selected, the data logger
must assert its DTR output before and during the transmission. Note a standard RS-232 cable
normally connects pin-4 (DTR) of a data terminal equipment (DTE) device [your data logger] to
pin-4 (DSR) of a data communications equipment (DCE) [the H-4400].