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7.6 SETUP CUST
The Model 5081-T contains a curve fitting program that can create a second order curve for
3 to 5 user supplied data points. If only two points are entered, a straight line will be used.
These points are from numerical data previously collected that is entered via the keypad. All
data point must be approximately the same reference temperature.
Best results will be obtained by selecting data points that are representative of the typical
operating range and are at least 5% different conductivity values. Plotting the graph of con-
ductivity vs. concentration for the data points of interest before using this procedure is highly
recommended. This will insure that unsuitable points (i.e. two concentrations with the same
conductivity) and critical points (that best describe the curve) can be determined. All data
points should be either on the rising side of the conductivity versus concentration curve or the
falling side, but not both (i.e. both side of the conductivity maximum or minimum). Following
these guideline will simplify the data entry procedure and provide optimum results.
The first point entered "COnd 1"should be at the normal operating condition. Other points,
both above and below "COnd 1" can then be entered. Very nonlinear conductivity curves may
need additional points to characterize these regions. Do not use the same data for more than
one point and only use real data - do not interpolate.
NOTE
The default values for the custom curve are three data points, reference tempera-
ture of 25°C and a linear temperature slope of 2%/°C. This combination will yield
the best results in most applications. If normal operation is over 40°C or under
10°C, the reference temperature should be changed to the normal process tem-
perature. If the temperature slope at the reference temperature is known, it can be
used.
7.6.1 Procedure
MODEL 5081-T SECTION 7.0
PROGRAMMING
1. From the main menu, press PROG; then press NEXT four times. SetUP CuSt will
appear.
2. Press ENTER. t rEF will appear. If needed, change the reference temperature from
the factory default 25°C (77°F) to a different reference temperature for the process.
Press ENTER.
3. UnIt will appear. Press or
to select the desired measurement units: µS (micro-
Siemens), nS (milliSiemens), none (no units displayed), % (percent), or ppn (parts per
million); then press ENTER.
4. NUM PtS will appear. Press or
to select the desired number of data points for a
custom conductivity curve. Selecting 2 will generate a linear relationship for conductiv-
ity and concentration at the given reference temperature.
a. Enter the concentration for Pt. 1 (displayed as µS 1). Press ENTER.
b. Enter the known conductivity for Pt. 1 in µS/cm. Press ENTER.
c. Complete this process for additional known data points. Press ENTER.
5. CALC Cust will appear. Press ENTER. PrOCESSinG will appear briefly; then APPLY
CUSt will appear. Press ENTER to enter the custom curve into memory and return to
the SetUP CuSt screen.
The Custom curve will now be used to display and output all conductivity (or resistivity)
measurements if Cust is selected in the Display menu for measurement type.
PROGRAM
U!
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SHI
EXIT NEXT ENTER
PROGRAM
>P5U
EXIT NEXT ENTER
PROGRAM
8VO!
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:UT
EXIT NEXT ENTER
PROGRAM
/DNF!
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/VTU
EXIT NEXT ENTER
U!
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SHI!
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>PLUT
µ
µµ<
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RUT!
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%
µ
µµ<!
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#
/QPG!
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#!
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"c"""
µ
µµ<!
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$!
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"c"""
/QPG!
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$!
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"c"""
µ
µµ<!
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%!
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"c"""
/QPG!
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%!
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"c"""
/DNF!
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/QPG
-RRNY!
!
/VTU