Hanna Instruments HI 9931 - Manual (Page 14)

14
• The contoller provides for automatic fail-safe secruity automatic fail-safe secruity automatic fail-safe secruity automatic fail-safe secruity automatic fail-safe secruity by
activating the alarm if there is a power failure, regardless of
whether the NC or NO configurations were chosen.
• The alarm is also activated if the overdosage time is exceeded.
The maximum time that the relay contacts
remain active continuously can be set from 1
to 10 minutes.
• Once in an alarm condition, the alarm contact
remains activated until the switch is put in the
manual position or the measurements return to normal values.
TIMER
MINUTES
1 10
2.5
5
7.5
RECORDER OUTPUT CONNECTIONS
• The recorder output contacts are iso-
lated from the controller circuitry to avoid
interference. Select 0 to 20 mA or 4 to 20
mA with the switch (see 15 - Functional
Diagram) before wiring the recorder to the terminals. The output
mA value is proportional and is the measured conductivity or TDS
over the entire range. For example, when HI 9931 measures
2.00 mS/cm (EC), the output values are 4 mA or 7.2 mA based
on whether the 0-20 or 4-20 output was respectively selected.
Likewise, when HI 9934 measures 1500 ppm (mg/L), the output
values are 15 mA or 16 mA based on whether the 0-20 or 4-20
output was selected.
Output mA
selector
0/20 4/20
RECORDER
SET EC
ALARM
LINE
0 SECONDS mS 1.6 0
TIMER MINUTES 90
45
FINE COARSE
PROPORTIONAL SETTINGS
ALARM AUTO
MANUAL
SET
READ
FERT.
SET POINT
HI 9931
1 10
2.5 5 7.5 0.8
mS
EC
FEED
SLOPE CAL ZERO CAL
EC
0
1
2
ALARM
mA OUTPUT 4/20 0/20
mS
TEMPERATURE COMPENSATION
Temperature affects conductivity and TDS mesurements considerably
(approx. 2% per °C). You however do not need to worry about
having to compensate for this or go through complicated calculations
since all three probes recommended in this manual (HI 7638,
HI 3002 and HI 3001D) compensate for temperature automatically.