Detcon RXT-300 - Manual (Page 23)

RXT-300 SmartWireless™
RXT-300 Wireless IM Rev. 2.0 Page 17 of 41
as well as process and store the alarm state of the sensor. The Sensor Station RXT-300 will transmit all its
sensor data to the rest of the network when it is polled by the Master RXT-300. This data is then stored by
every RXT-300 on the network and available for those RXT-300s to perform alarm processing or for user
visibility through a HMI Station.
The Modbus™ interface only supports sensors or a controller not both, so if one or more sensors are attached
it the Modbus™ interface it will not support a controller or HMI. If the sensors only use the 4-20mA inputs
then a Modbus™ controller or HMI can be attached.
The Modbus™ sensors are defined in the system configuration as being attached to a particular RXT-300 and
the Modbus™ address and registers that are to be read. Additionally the register that contains the sensor
concentration is identified and what alarm thresholds are. The RXT-300 will read all registers as configured,
store them locally and then process the concentration for an alarm event. If Detcon sensors are used,
additional fault or calibration info is also processed and made available for display on the HMI Stations.
The two 4-20mA sensor inputs can represent up to two separate sensors if enabled. Their Modbus™ address
becomes the RXT-300 they are attached to. The RXT-300 will actually store the readings for the two inputs
into two separate registers on the RXT-300. A 4-20mA sensor type can be setup that will read this register and
process alarms much like sensors on the Modbus™ interface.
3.4 Alarm Station Operation
Alarms can come from several different sources. These not only include sensors but RXT-300s and network
based alarm events. These alarm events are eventually mapped to just four alarm outputs, Alarm 1-4 on an
RXT-300. All RXT-300s will generate alarms on their alarm outputs but most stations do not have any alarm
devices attached. A list of possible alarm events are shown below:
• Sensor Threshold Settings, Ascending or Descending
• Sensor Communication Errors
• Sensor Fault conditions – Detcon sensors types only
• Battery Threshold on remaining time
• Battery Communication Error (fault)
• Network Communication Error – one of more RXT-300s offline
• Network Down – no Master RXT-300
Mapping of these alarm events is configurable to any one of the Alarm 1-4 outputs on a device by device basis
but defaults are generally used. Alarms can also be grouped using Zones which is covered later. Each
RXT-300 will process all alarms for itself which will include sensors if any, battery status and network status.
Upon detection of an alarm event the local Alarm outputs will be updated. This information is disseminated
later when that RXT-300 is polled by the Master RXT-300 and at this point all RXT-300s will receive the new
alarm state and update their alarm outputs accordingly.
Detcon Alarm Stations that can operate off of a single Detcon Smart Battery pack will have two alarm devices
attached. Alarm devices were selected to minimize the power consumption and yet maximize the alarm
coverage. Figure 15 shows units designed for installation and use in Hazardous duty, corrosive work
environments rated at Class 1, Division 2, Groups E, F, and G.