User Guide

82
SOLUTION COMPENSATION
The instrument is provided with a solution compensation func-
tion which can be enabled through setup menu (setup item
S.00). This function is a compensation curve (actually a line)
defined through 2 couples of pH and temperature values:
• point #1: pH
1
, T
1
• point #2: pH
2
, T
2
The only restriction on the values of pH and temperatures is
|T
1
-T
2
| U 1.0°C.
When the solution compensation is enabled, the pH reading
will be equal to:
pH (with solution compensation) = pH (without solution com-
pensation) + [(pH
1
-pH
2
)/(T
1
-T
2
) x (25-T
2
) + pH
2
] - [(pH
1
-pH
2
)/
(T
1
-T
2
) x (T-T
2
) + pH
2
]
where T is the current temperature reading (Celsius degree
units).
With this kind of compensation formula, the pH value with
solution compensation will be the same (i.e. (pH
1
-pH
2
)/(T
1
-
T
2
) x (25-T
2
) + pH
2
) at point #1 and point #2.
This solution compensation feature is useful, for example, in
the following case:
HI 504 is measuring pH=pH
1
at temperature T
1
; a sample
is taken out and carried in the laboratory room to be checked
with a reference pH-meter; in the meantime the temperature
decreases to T
2
and also the pH value measured with the
reference pH-meter changes to pH
2
(due to the chemical
properties of the solution); if the same solution compensation
formula is applied in both HI 504 and the reference pH-
meter, they will read the same value.
To enable the solution compensation, set the S.00 item in the
setup menu to “ON”.
The solution compensation is disabled in any case when cali-
brating pH.