Hanna Instruments HI 9912 - Manual (Page 17)

17
ALARM DOSING TIME
MINUTES
1 10
2.5
5
7.5
e.g. ORP proportional control
Setpoint = 750 mV
Measured value = 725 mV
Delta = 750 - 725 = 25 mV
Proportional settings = mV set to 100 and time cycle to 60 seconds
The controller will be dosing
oxidants to increase redox to
the desired value. Since it is
25/100 = 25% away from
the ideal setting, it will keep
the dosing contacts activated
for 25% of the time over the
predetermined 60 seconds.
The terminals are hence acti-
vated for 15 seconds and off
for 45 seconds until the next
cycle.
0
SECONDS mV
200 0 90
PROPORTIONAL SETTINGS
50 150
OVERDOSAGE TIMERS OVERDOSAGE TIMERS OVERDOSAGE TIMERS OVERDOSAGE TIMERS OVERDOSAGE TIMERS
HI 9912 provides for two independent overdosage timers. The
operator can set the maximum amount of time that the dosage
terminals should continuously remain acti-
vated from 1 to 10 minutes . Should this
period elapse, the alarm terminals are acti-
vated (and dosage disactivated to ensure
that chemicals have not run out or pumps
or electrovalves have not ceased to function
properly).
D mV
Seconds 15 30 45 60
25
50
75
100
15 30 45 60