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pH/ORP PROBE CHECK
The pH electrode and the reference electrode for both pH
and ORP can be automatically monitored through HI 504.
Setup items involved are I.13 (pH electrode impedance test
enable), I.14 (reference electrode impedance test enable),
I.15 (maximum reference electrode impedance) and I.04 (po-
tential matching pin enable).
A "pH electrode broken or leakage error" (error code: 10) is
generated whenever the pH electrode impedance is less than
approximately 1 M . This error can be due to breakage of the
electrode glass or short circuits caused by moisture or dirt.
A "reference electrode broken or dirty or not immersed" error
(error code: 11) is generated whenever the reference elec-
trode impedance is greater than the value set in item I.15
(maximum reference electrode impedance range is 0.5 to
100.0 K , default is 50.0 K ). This error can be due to
soiling of the reference electrode. It can occur also when
either the reference electrode or the matching pin are not
immersed in the solution. An automatic cleaning procedure
can be triggered by this error (see the "Alarm - Error configu-
ration" section for more details).
The pH electrode test is performed when the following condi-
tions are satisfied:
• the test has been enabled through the setup item I.13;
• the device is in one of the following modes: idle, last cali-
bration data scrolling, event log file scrolling;
• the device is not in hold mode;
• the device is configured to measure pH.
Note
If an amplified electrode is used, the pH electrode test
must be disabled through the setup item I.13.
The reference electrode test is performed when the following
conditions are satisfied:
• the matching pin has been enabled through the setup
item I.04;
• the test has been enabled through the setup item I.14;
• the device is in one of the following modes: idle, last cali-
bration data scrolling, event log file scrolling;
• the device is not in hold mode.
Note
When testing or calibrating the instrument through a
pH/ORP simulator like HI 931001 or HI 8427, tempo-
rarily set the items I.13 and I.04 to "OFF".
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:
• point #2:
The only restriction on the values of pH and temperatures is
|T
-T
|
1.0°C.
U
1
2
When the solution compensation is enabled, the pH reading
will be equal to:
pH (with solution compensation) = pH (without solution com-
pensation) + [(pH
(T
-T
) x (T-T
1
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
T
) x (25-T
2
2
This solution compensation feature is useful, for example, in
the following case:
HI 504 is measuring pH=pH
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
reference pH-meter changes to pH
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.
pH
, T
1
1
pH
, T
2
2
-pH
)/(T
-T
) x (25-T
) + pH
] - [(pH
1
2
1
2
2
2
) + pH
]
2
2
) + pH
) at point #1 and point #2.
2
at temperature T
1
1
and also the pH value measured with the
2
(due to the chemical
2
-pH
)/
1
2
-pH
)/(T
-
1
2
1
; a sample
83
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- Calibration Mode
- Setup Mode
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