21
20
SETPOINT ADJUSTMENTS
• Move the display selector switch to SET.
• With a small screwdriver adjust the SET COARSE trimmer to
display a value close to the desired setpoint e.g. 7.00.
• Adjust the SET FINE trimmer to display the exact setpoint value.
• Once the desired setpoint is achieved, move the display selector
switch back to MEASURE.
ACID OR BASE SELECTION (BL 7916 only)
If an acid chemical is to be dosed, move the
ACID/BASE switch to ACID. This means that
the pump will dose when pH measurements
are higher than the setpoint.
If an alkaline chemical is to be dosed, move
the ACID/BASE switch to BASE. This means
that the pump will dose when pH measure-
ments are lower than the setpoint.
REDUCING OR OXIDIZING SELECTION (BL 7917 only)
If a reducing chemical is to be dosed, move
the RED/OXID switch to RED. This means that
the pump will dose when redox measure-
ments are higher than the setpoint.
If an oxidizing chemical is to be dosed, move
the RED/OXID switch to OXID. This means
that the pump will dose when the redox
measurements are lower than the setpoint.
The wires and cables needed for all connections can be fed through
the two cable fittings located below the terminals. It is important to
attach these cables properly because pump vibrations could loosen
them. Replace the transparent cover and fasten the screws.
For example, a level controller can be placed in the tank of the liquid
being dosed so that the pump is stopped when the chemicals are
exhausted.
MANUAL
An auxiliary switch can be connected to these terminals to force the
unit to pump whatever value is measured by the controller. This
might be needed for example when the pump needs to be primed.
AUXILIARY CONTACT
The controller can drive a relay when the measure overtakes the
setpoint. The contact available on the terminals can be normally open
or closed. It can be used as a switch to drive an external mixer when
the pump is dosing, or can activate an auxiliary pump or any other
device. With
BL 7916
, the contact can be selected to remain open
when the pH value is within the set limits (the pump is not dosing)
and closed when the pump is dosing or viceversa.
By shorting the Common (middle) terminal with the NO or NC
terminal on the driving circuit inside the controller section, a normally
open or a normally closed state can be achieved, as shown below:
ALARM CONTACT
If the reading drifts from the setpoint by more than ±2.00 pH in
BL 7916
and ±200 mV in
BL 7917
, an external alarm can be
activated. The contact is rated at 2 amps at 220VAC. No power is
supplied through the system and it is an open/closed contact only.
With
BL 7916
, the contact can be selected to be closed when the
alarm is activated and open when the alarm is off or viceversa. Short
the middle terminal located on the driving circuit inside the controller
section with the NO or NC terminal (see above).
4-20 mA ISOLATED OUTPUT
A 4-20 mA proportional output is available in these connections:
4 mA=0 pH; 20 mA=14 pH (BL 7916)
and
4 mA=-999 mV; 20 mA=+999 mV (BL 7917).
The output is optically isolated.