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Field contact circuits
Alarm channel
functions
6
The electrical contacts of the devices sensing the
process condition must be potential-free while
the annunciator unit itself generates the 48 V dc
field contact voltage. This specification also
applies to the remote control inputs.
The power unit supplying voltage to the field
contacts also provides a full galvanic isolation
between the field contact circuits and the elec-
tronic circuits of the annunciator unit it self as
well as the system earth. The channel inputs are
provided with transient suppression circuits and
input voltage limiters.
Field
contact
Fig. 3. Principle of alarm channel input.
An alarm channel is composed of a number of
functional blocks illustrated below. The lists of
variables underneath some of the blocks indi-
cate that a certain parameter can be selected
48 V
Field
contact
FIELD
CONTACT
SELECTION
0 = NO field contact
Galvanic isolation
1 = NC field contact
and transient
2 = NO field contact,
suppression
no return function
3 = NC field contact,
no return function
4 = NO and NC field
contact
5 = pulse counter,
counts on closing
function
6 = pulse counter,
counts on opening
function
7 = pulse counter,
counts on both
closing and opening
function
Fig. 4. Block schemating diagram for an alarm channel.
The alarm channels can be individually pro-
grammed for operation from normally closed
(NC) or from normally open (NO) contacts.
The annunciator is provided with an integrated
field contact voltage supervision function. When
a fault is detected the LED indicator marked
"FAULT" on the front panel is switched on and
internal supervision output relay operates. The
fault message can also be transmitted over the
serial communication link to the higher system
levels.
TRANSIENT
SUPPRESSION
0 V
From the internal
48 V
supply module
48 VDC
from a set of given values, i.e. the parameter can
be programmed. The selected parameter is shown
in the numerical display when called up during
the programming.
Interlocking
output (0)
INPUT DELAY
RESET DELAY
0 = 5 ms
0 = 5 ms
1 = 20 ms
1 = 20 ms
2 = 100 ms
2 = 100 ms
3 = 1 s
3 = 1 s
4 = 5 s
4 = 5 s
5 = 20 s
5 = 20 s
6 = 60 s
6 = 60 s
7 = 160 s
7 = 160 s
Galvanic isolation
Reset
Ack.
Silence
1
SEQUENCE
LOGICS
Alarm indicator
0 = sequence 0-4
Audible alarm
1 = sequence 0-4,
audible alarm
also at dis-
appering alarm
2 = field contact
following
Reflash A
Channel
interlocking
interlocking
input (1)
input (2)
To alarm
channel
Reflash B
&
Reflash A
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