Xylem PHIX COMPACT pH and Redox Transmitter - Manual (Page 16)

16
Buffer Adjustment
GB pHix Compact Manual 100318
Buffer adjustment
General
In order to ensure a precise and stable pH
measurement, pHix
® Compact must be buf-
fer adjusted with regular intervals.
Buffer adjustment is a calibration, which
is carried out in practice by dipping pHix
®
Compact in solutions (buffers) with known
pH values. The calibration is made by using
these known pH values as a reference point.
pHix
® Compact is buffer adjusted using 2
buffers with pH values of 4 and 7 (acidic
range) or pH values of 7 and 10 (alkalic
range). For measurements around pH 7
(neutral) both buffers can be used.
The sequence of different pH buffer soluti-
ons is not important. pHix
® Compact auto-
matically detects which buffer is used for
ajusting the point of origin, and which buffer
is used for ajusting the slope (sensitivity).
The first reference point sets the correct
zero point for the measurement curve, and
the second reference point sets the correct
slope for the measurement curve.
pHix
® Compact is as standard delivered to
use buffer values at the values 4, 7 and 10,
but other values can be chosen via HART
®
communication.
Buffer liquid
Buffer liquid is delivered as ready-to-use
solutions with the pH values 4, 7 and 10.
During the buffer adjustment, pHix
®
Compact is calibrated in accordance with
the pH values of the buffer solutions. It is
therefore important to use as accurate buf-
fer solutions as possible, i.e. a pH 7 buffer
solution really has a pH value of exactly 7.
MJK delivers buffer solutions for both
pH og redox calibration.
The pH value of the buffer liquid is depen-
dant of the temperature, and the stated pH
value is valid at 25 °C.
Buffer liquid has limited lifetime. Bufferliquid
for pH 4 and 7 has a life time of approx. 1
year, and buffer liquid for pH 10 is so-
mewhat shorter.
Note, that buffer liquid with pH 10 is very
unstable, and should therefore be disposed
of no more than 1 hour after it has been
poured from the bottle.
First buffer adjustment with pH 7 as reference.
Second buffer adjustment with pH 4 as reference.