ELPRO 905U - Change of State Conditions

Chapter Three Operation
man_905-105_2.16 Page 29
to be reflected to an output on the module for alert purposes. The outputs on the module may also be
configured to reset after a specified timeout (digital outputs reset to “off”, analog outputs reset to 0
mA) allowing the system to turn off in a controlled manner e.g. a pump will never be left running
because of a system failure.
Note: The 905U will hop frequencies for each re-try transmission - each re-try will follow
at approx 0.5 sec after the last. However the 105U licensed fixed-frequency units will re-try
on the same frequency. In order to allow other users to clear the frequency channel, the
105U will wait a random time between 2 and 7 seconds between each retry. So a 905U will
complete all re-tries in less than 3 seconds, however a 105U will take 10 – 20 seconds.
Repeaters can be used in a system to increase range. Each 905U unit can be configured to act as a
repeater. When configuring an input to be mapped to an output, the communications path to the output
unit, including the repeater addresses is specified. The 905U acts as a store&forward repeater, that is,
the signal is decoded and then retransmitted “as new”.
Example Repeater Communications
Unit A DI 1 mapped to Unit D DO1 via Units B & C
Unit A Unit B
Repeater
Unit C
Repeater
Unit D
•
DI 1 is turned
on
• Transmit
• Receive
Acknowledge
• Receive
• Transmit on with
Acknowledge
• Receive
Acknowledge
• Receive
• Transmit on with
Acknowledge
• Receive
Acknowledge
•
Receive
• Transmit
acknowledge
• DO 1 is
turned on
3.1.2 Change of state conditions
The module transmits a data message whenever it detects a "change-of-state" on one of its input
signals. A "change-of-state" of a digital or digital internal input is a change from "off" to "on" or vice-
versa provided the change is sustained for 0.5 second (i.e. 0.5 second debounce). The debounce delay
is configurable.
In addition to "change-of-state" transmissions, each module will transmit the status of each input to its
corresponding output every ten minutes (configurable). These updates mean that the outputs are set to
the current input values regularly, even where no “change-of-state” has occurred. These update
transmissions increase the accuracy of the output and give extra system reliability.