Adjustement of setpoint(s), Proportional control, For ph – Hanna Instruments HI 9912 User Manual

Page 15: Dosing direction, For orp

Make sure that the electrode (and any ground probe) is properly
installed and calibrated (see the preceding pages).

FOR pH

Simply turn the pH ACID FEED dial (see 3 - Func-
tional Diagram) and choose the desired value between
6 and 8 pH.

DOSING DIRECTION

The dosing terminals are activated when the pH value exceeds the
setpoint. HI 9912 will then dose acidic solutions until the user-selected
setpoint is reached.

ADJUSTEMENT OF SETPOINT(S)

FOR ORP

Simply turn the ORP OXID FEED dial (see 11 -
Functional Diagram) and choose the desired value
between 500 and 900 mV

DOSING DIRECTION

The dosing terminals are activated when the ORP falls below the
setpoint. HI 9912 will dose oxidants until the user-selected setpoint is
reached.

ALARM

SET

FEED

ACID

500

900

SET

FEED

ALARM

OXID

700

SECONDS

2.0

PROPORTIONAL SETTINGS

0.5

1.5

SECONDS

200

PROPORTIONAL SETTINGS

150

PROPORTIONAL CONTROL

In order to optimize the controlling process and reduce the amount of
chemicals used, it is recommended to use a proportional dosage
appropriate for the system.
HI 9912 allows for a proportional
band of 0 to 2.0 pH and 0 to
200 mV (delta) as well as two
independent time cycles from 0 to
90 seconds. The proportional dos-
age is obtained by personalizing a
current pulse whose height equals
the pH or ORP proportional delta
and the length corresponds to the
selected time cycle.
The controller will enter proportional dosage at setpoint

proportional dosage at setpoint

minus

minus (in case of ORP) or plus

or plus

or plus (for pH) the preselected delta

the preselected delta

the preselected delta.

It will then keep the dosing relays activated for a period proportional