Chapter 3 - Device Overview
UNITROL 1020 User Manual 3BHS335648 E82 65
Changeover Logic
to DO
port
CAN communication data flow
Measurements & Status and
Setpoints for DCH Follow-Up
and user interfaces
AND
OR
OR
DCH Comm. Status
2nd. Channel Trip
2nd. Channel Alarm 1
DCH
Measurement &
Communication
Enable DCH Communication
when
2nd. Channel measurements & Status
will not be available if DCH Comm. is
not enabled or if DCH Comm. Status
Ok is equal to zero (i.e. bad quality).
Trip status
Alarm 1 status
Changeover status is latched
when it goes from zero-to-one
(edge detection)
Reset
Clears (to zero) the latched
Changeover status only if
the AND output is also zero.
Changeover status
to second
channel
Alarm 2 status
Figure 3-12 Channel Changeover logic and configuration.
Check box for Alarm & Trip (also 2nd. Channel)
AND
DCH
Measurement &
Communication
A A
1 (enable)
AND
DCH
Measurement &
Communication
A
0
0 (disable)
A A
0 (logic)A
Check box for DCH communication
Figure 3-13 Configuration checkboxes rules.
The Changeover output is intended to be used together with the Standby input, in order
to activate the Redundant channel and deactivate the Main one. The Standby status can
be set via Remote Access or via a digital input (common case). Figure 3-14 shows a
typical example of Changeover output to set the Redundant Channel to Standby or Active
mode. The ResetAlarm input is normally used to clear the latch memory of Changeover
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