LX Series Unit Ventilator Controller User's Guide
52
Network Outputs
The network variables have several important attributes in common. These
attributes include Heartbeat, Send on Delta, and Throttle.
Table 7 defines the network variable attributes. Table 8 describes the network
inputs.
Table 7: Network Outputs
Attribute
Description
Heartbeat
Heartbeat is the maximum amount of time that must pass before the network
variable automatically transmits. The presence of the heartbeat attribute
indicates that functions are proceeding normally. Failure to receive a signal at
the other node within a heartbeat interval causes an alarm message to be
sent over the network.
Heartbeat is like a countdown timer. Only when the heartbeat timer reaches
zero is the heartbeat message sent. Every time that a message is sent, the
Heartbeat timer resets to the full heartbeat value.
Heartbeat signals are not always sent. If the monitored data changes more
than is required by the Send on Delta setting within a shorter period of time
than the heartbeat, the data is sent on the network and the heartbeat
message is not sent. Instead, the heartbeat timer is reset and begins to count
down again.
Heartbeat provides a method of ensuring that points have not lost connection
and that the network is functioning. Whereas throttle restricts how often
messages are sent, heartbeat ensures that messages are sent regularly.
Heartbeat is disabled by setting it to zero.
Send on Delta
Send on Delta causes a message to be sent when the monitored data
changes by a previously set proportion. Send on Delta restricts extraneous
network noise by allowing only signals that indicate a meaningful amount of
change.
If the monitored data does not change for a period of time equal to the
heartbeat interval, the data is sent as a heartbeat signal.
Throttle
Throttle sets the minimum update period. Throttle acts as a limit on excessive
network traffic. If the value of a point on the network is constantly fluctuating
at a rapid rate and is set to Send on Delta, the network can be flooded by data
from that point. Throttle prevents the variable from transmitting more than
once every minimum update period regardless of how many fluctuations have
occurred during that period. For example, rapid motion of the damper could
drastically increase network traffic. Damper oscillations could also cause
network traffic problems if data were sent on every cycle of oscillation.
Throttle can prevent network congestion in either of these cases by limiting
the number of sends per time interval to a meaningful number.
Throttle units are in seconds. The larger the throttle number, the less
frequently the network variable is transmitted.
You can disable throttle by setting it to zero.
Table 8: Network Inputs
Attribute
Description
Heartbeat
The Heartbeat effect on a network input is set to the maximum time period
that the network variable waits for a message before entering the heartbeat
failure state. When a heartbeat failure state is entered, the value becomes
invalid and an alarm is sent.
Persistent
When the network variable is marked as persistent, the value is written to
EEPROM. Once written to EEPROM, the network variable value is preserved
through power outs and resets. Every time a new network variable value is
received, the new value is written into EEPROM.
Because EEPROM can only accept a limited number of data writes, be
careful how you use the persistent attribute. See the
section for more information.
