Chapter 3 - Device Overview
64 3BHS335648 E82 UNITROL 1020 User Manual
Alarm output toggling
Supervision and monitor alarms can be assigned for digital outputs as a summary alarm.
If a single monitor function is triggered, the output becomes active and the status is
latched.
The user can activate the toggling function by means of a parameter if the monitor
function detects a new alarm again. In this case the digital output linked to the alarm will
be deactivated for 1 sec (toggled off) and reactivated again (toggled on).
Channel Changeover Logic
As shown in Figure 3-12, the Changeover status is the output of the AND-gate which
depends on the Alarm and Trip Status from the current channel, Alarm and Trip Status
from the Second Channel and the DCH Communication Status which is an indication of
the communication quality between both channels.
The DCH Communication refers to the data transmitted over CAN between both
channels, and it contains setpoint information, measurements, status signals (including
Alarm and Trip) and others. The status of this communication is logical one (good) if data
coming from the Double Channel feature is received well and free of errors (CRC check).
On the other hand, the Communication Status is logical zero (bad) if the received data
contained errors, the communication was not enabled (no data received) and/or the
configuration was not set properly. Alarm and Trip from the Second Channel should be
configured using the DCH Supervision in the other channel.
To increase the flexibility, the Changeover dependency on Alarm and Trip status is
configurable; i.e. checkboxes allowing to configure whether these signals are part of the
AND and OR gate inputs of the logic decision (Figure 3-12). Each checkbox output is
determined according to the rules shown in Figure 3-13. An important setting is the
checkbox connected to the DCH Communication Status, which additionally lets the signal
pass through until the input of the AND gate. It also enables the DCH Communication
over CAN. The DCH Communication should be enabled to use the Changeover
functionality; otherwise the Changeover Status will be zero all the time (see Figure 3-12
and Figure 3-13).
The decision logic from Figure 3-12 shows that once the DCH Communication is
enabled, the dependency of Changeover Status is defined according to the checkbox
configuration and the Alarm and Trip status from both channels. When, for instance, the
checkboxes are configured according to Figure 3-12, the Changeover Status will be
logical one when: the Trip Status from the current channel is equal to one, the Trip Status
from the Second Channel is equal to zero (i.e. no trip in the Second Channel and it is
ready to takeover) and the Communication Status is equal to one (data from the Second
Channel is being received correctly).
The Changeover status value is latched (retains the value) when the AND gate output
changes from zero-to-one. The latched value may be cleared (to zero) using the Reset
command only if the output of the AND gate is already zero as well.
The Changeover status can be assigned to a digital output signal from the AVR. When
compared with Alarm and Trip DO signals, the DO assigned for Changeover always
outputs the Changeover Status disregarding whether the channel is Standby or Active;
for Changeover DO, this cannot be configured as it is for Alarm and Trip.
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