Hanna Instruments HI 8711 - Manual (Page 23)

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• •• •• CONSENT contacts (HI 8710 and HI 8720,
see picture, terminals 3 and 4): these contacts
(max. 2A, 240V) are used for reduction and
oxidation reactions when the pH controller
works in conjunction with an ORP controller and vice versa.
In these applications, the consent contacts of both meters are
connected together to link the ORP and pH controllers, so that ORP
dosage will occur only if the actual pH value is correct. This feature
avoids overdosages which may lead to undesirable pollution.
For HI 8710, the "Consent" contacts (terminals
3 and 4) can be left open if the instrument
is used independently as pH controller only.
For HI 8720, the "Consent" contacts (terminals
3 and 4) should be shorted if the instrument
is used independently as ORP controller only.
• •• •• ALARM contacts (HI 8710, HI8711 and
HI8720) (see picture terminals 5, 6): If the
pH or ORP measurement are inside the set
value tolerance the alarm contact is closed
and ALARM LED is OFF (alarm is not active).
If the pH or ORP measurement is not within
the set value tolerance, the alarm contact is
opened and ALARM LED blinks (alarm is
active). This ensures that a power down condition will generate an
alarm condition.
• •• •• To set the overtime dosing period rotate the
overtime knob to the proper position. The
time can be set between approx 5 min to 60
min (from MIN to MAX position). To disable
the overtime dosage feature, make a short
with a jumper wire between the terminals of
the proper connector (see picture, terminals
1 and 2).
Note: All external cables connected to the rear
panel should be ended with cable lugs.
• •• •• ALK. contact (HI 8711) (see picture, terminals
3 and 4): these contacts are used to connect
the dosing pump for base, and act as a
switch for the power to the drive.