Fema B Series, User Manual, Page: 20 / 36

FEMA ELECTRÓNICA . SERIES B . Models Bxx-RTU
20
1.21.8 Alarms
The instrument manages 3 independent internal alarms,
each one controlling the activation of an optional relay,
transistor or control SSR output. Optional modules
(see
section 2)
are installed at the free slots inside the instru -
ment
(see section 1.7)
. B24 and B44 formats have 2 free
slots for output and control modules, while B26 and B46
formats have 3 free slots for output and control modules.
The instrument has 3 front leds that reflect the state of
the 3 internal alarms. These leds are only for local help
during installation, as they are not appropriate for long
distance reading.
Each alarm controls the activation of the relay, transis -
tor or control SSR installed on its associated slot, and the
front led.
• Alarms in ‘Full slave’ mode
In ‘Full slave’ mode, the alarms are controlled through the
bus. By default the control is performed by writing to the
‘coils’. to activate control by writing to ‘registers’ see sec -
tion
(see section 1.21.6)
.
In ‘Full slave’ mode an alarm can be associated to the
watchdog. This alarm will activate when the watchdog er -
ror activates
(see section 1.21.4)
. This function allows to
activate a relay to inform about loss of communication.
• Alarms in ‘Process slave’ mode
In ‘Process slave’ mode, the alarms are controlled locally
at the instrument, and the operator must manually con -
figure them.
Each alarm has several parameters for configuration,
starting with the usual setpoint, hysteresis and maximum
(alarm active when reading is higher than setpoint) or
minimum (alarm active when reading is lower than mini -
mum) alarm types
(see Figure 6) .
Each alarm can configure independent activation and
deactivation delays. These delays affect the alarm as a
whole, and the delay will affect the front led and the as -
sociated relay.
Configuring a second setpoint creates ‘windowed alarms’.
The windowed alarm controls with a single relay output
if the reading is inside or outside the values defined (see
Figure 7)
.
Activate the ‘inverted relay’ function to invert the activa -
tion logic of the associated relay.
Activate the ‘locked alarms’ function will force the opera
-
tor to interact with the instrument when an alarm has
been activated. Once activated, the alarm will remain
locked at active state, even if the reading returns to a val -
ue below setpoint, until the operator manually unlocks
the alarms pressing the front key ‘LE’ (or the remote key
‘LE’, see section
3.1
).
Reading
t
setpoint
hysteresis
Alarm as maximum, no
hysteresis, no delays
on
off
activation
delay
on
off
deactivation
delay
Alarm as maximum,
hysteresis and delays
on
off
Alarm as minimum, no
hysteresis, no delays
t
t
t
Figure 6 - Examples of alarm with 1 setpoint
Reading
t
Setpoint 2
Setpoint 1
Alarm as minimum, with
double setpoint, no hyster -
esis, no delays
on
off
t
Figure 7 - Example of alarm with 2 setpoints