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MODEL 54eA SECTION 5.0
SOFTWARE CONFIGURATION
5.8 CONFIGURING THE pH MEASUREMENT (continued)
Temp coeff : 0.000
Operate iso: 7.00 pH
Sensor iso: 7.00 pH
Exit Enter
Stabilize pH and Stabilize time: For the controller to accept cal-
ibration data, the pH must remain within a specified range for a
specified period of time. The default values are 0.01 pH for 10 sec-
onds. Using a small pH value and a large time provides the best
protection against calibration while the reading is still changing.
8. In many industries pH is used and reported at a reference tempera-
ture of 25°C. Correcting a pH reading to 25°C is often referred to as
a solution temperature correction. To perform the correction, the solu-
tion temperature coefficient must be known.
a. With the cursor on "Temperature coeff", press Enter (F4).
b. Use the é and ê keys to move through the list of items. To make
a change press Edit (F4). Use the arrow keys to change the set-
ting to the desired value and press Save (F4). For allowed ranges
see Table 5-1.
Temp coeff: Enter the temperature coefficient in units of ΔpH/°C.
If the pH decreases as temperature increases, the temperature
coefficient is negative. The temperature coefficient must usually
be determined empirically.
APPLICATION WARNING
If pH is being measured for the purposes of correct-
ing a free chlorine reading, do NOT use solution tem-
perature correction. Keep the temperature coeffi-
cient at 0.000 pH/°C.
Operate iso: Entering a temperature coefficient ALWAYS causes
the operating isopotential to change from the normal value of
7.00. When programming the controller to perform solution tem-
perature compensation, ALWAYS enter the solution temperature
coefficient and allow the transmitter to calculate the operating
isopotential pH.
Sensor iso: The isopotential pH is the pH at which the cell volt-
age is independent of temperature. Most sensors have an isopo-
tential pH fairly close to 7.0, so the default value is 7.00. Certain
specialized pH electrodes have isopotential pH significantly dif-
ferent from 7.0.
NOTE
Do NOT change the isopotential pH of the con-
troller unless you are thoroughly familiar with the
role of isopotential points in pH measurements OR
the sensor operating instructions specifically state
the isopotential pH is a value other than pH 7.
pH diagnostics
pH calibration
Temperature coeff
Exit Enter