Hanna Instruments bl 7917 用户手册
20
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.
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.
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:
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 BL7917, 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).
BL 7916 and ±200 mV in BL7917, 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.