13
ALARM CONNECTIONS
• The alarm threshold is user-selectable from
0.5 to 2.5 pH for
HI9910
and
HI9911
, or
from 50 to 250 mV for
HI9920
, by turning
the alarm trimmer with a small screwdriver.
If the actual measurement is above or below the setpoint by a
value greater than the selected threshold, the alarm terminal is
activated. The alarm can be configured as Normally Closed (“NC”)
by connecting the external device to the COM and NC terminals or
Normally Open (“NO”) by connecting the external device to the
COM and NO terminals.
• When the alarm is activated, the alarm LED turns on and the alarm
contacts will open or close, triggering the external connected device.
When the alarm is activated all the other terminals (such as dosing
relays) are disactivated.
• The alarm ON/OFF switch can only disable the
alarm terminal (e.g. the buzzer stops sound),
while all the other functions, such as disactiva-
tion of the dosing relays, are not affected.
• The controllers provide for automatic fail-safe security by activating
the alarm if there is a power failure, regardless of whether the NC
or NO configurations were chosen.
• The alarm is also activated if the maximum
dosage time is exceeded. The overdosage timer
can be set from 1 to 10 minutes.
For
HI9911
, two timers can be independently
selected for acid and alkaline corrections.
• Once an alarm condition occurs, the alarm contact remains activated
until the switch is manually put in the off position or the measure-
ment returns to normal values.
