Appendix
A
|
Channel Specific Settings and Features
The meter evaluates the relationships between the three potentials E
1
, E
2
and E
3
and the three
concentrations C
1
, C
2
and C
3
. If the relationships indicate that blank correction is desired, a
blank will automatically be calculated and the non-linearity will be corrected for in a Nernstian
manner. If the appropriate conditions are not met, the blank is set at zero and each segment of
the multi-point calibration is treated independently.
When all three of the following conditions are met, blank correction is invoked.
1.
The concentration of the first standard is zero, or the slope of the electrode between the first
and second standards is less than the slope between the second and third.
2.
Potential differences between points are significant. For example, E
3
- E
1
> 10 mV
3.
The blank correction algorithm converges at reasonable blank and slope values. Conditions
in steps 1 and 2 prevent failure to converge in most situations. However, the slope will attain
any value necessary for convergence to a calculated blank value of 3 x C
3
.
When blank correction is implemented, the slope value for the electrode may be outside the
range of values normally considered acceptable during an ordinary calibration. For best results,
calibration standards should be close in range to the expected sample concentrations and
should bracket the expected sample concentration. When conditions 1, 2 and 3 are not met, the
calibration data is handled by the multi-point calibration method described earlier.
In calibrations with more than three points, a combination of methods is utilized. Automatic
blank correction is used if the lowest three points satisfy the criteria and multi-point calibration is
used for the other points. The slope calculated in the automatic blank correction algorithm and
the slopes for each additional segment are used to calculate the average slope.
Low Level Stability
V
ERSA
S
TAR
meters with a pH/ISE module offer the option to use the low level stability feature
when calibrating ion selective electrodes. The low level stability feature improves the accuracy
of low concentration ISE measurements by adjusting the timing for calibration points of low level
standards, allowing a longer stabilization time for the electrode in the calibration standards. The
stabilization time is typically extended to about three to five minutes per calibration point, but
will vary based on the actual readings from the electrode during calibration.
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Thermo
Scientific
Appendix
A
|
Channel Specific Settings and Features
LogR Temperature Technology
The V
ERSA
S
TAR
meter with pH/LogR measurement module allows direct temperature
measurement and temperature compensation using most standard
glass-bulb pH electrodes
and patented digital LogR technology.
LogR technology is based on using the electrical resistance of the pH-sensing glass-bulb as the
temperature source. The logarithm of the resistance of the bulb varies almost linearly with the
reciprocal of the absolute temperature. Almost all standard glass-bulb pH electrodes exhibit a
similar decrease in resistance with increasing temperature. To maximize LogR performance
and accuracy, a ROSS Ultra or ROSS pH electrode is recommended.
LogR Resistance vs. Temperature Graph
LogR Temperature Accuracy
Table 1 – Two Point LogR Temperature Calibration, Average Error at pH 3 and pH 11
Electrode
Average
Temp. Error
0 to 25 °C
(°C)
Average
Temp. Error
Above 20 °C *
(°C)
Average Temperature
Compensation Error
0 to 25 ºC
(pH Units)
Average Temperature
Compensation Error
Above 20 °C *
(°C)
8202BN
0.36
0.10
0.004
0.001
8203BN
0.13
0.02
0.002
0.000
8235BN
0.04
0.14
0.000
0.002
8256BN
0.22
0.06
0.003
0.001
8272BN
0.23
0.06
0.003
0.001
9202BN
0.21
0.06
0.003
0.001
9203BN
0.20
0.10
0.002
0.001
9206BN
0.29
0.06
0.003
0.001
9207BN
0.16
0.07
0.002
0.001
9256BN
0.27
0.07
0.003
0.001
9272BN
0.22
0.06
0.003
0.001
* For 20 °C temperature
compensation spans
Thermo Scientific
Orion V
ERSA
S
TAR
Meter User Manual
|
111
Appendix
A
|
Channel Specific Settings and Features
Table 2 – Three Point LogR Temperature Calibration, Average Error at pH 3 and pH 11
Electrode
Average Temp.
Error
0 to 25 °C
(°C)
Average Temp.
Error
Above 20 °C *
(°C)
Average Temperature
Compensation Error
0 to 25 ºC
(pH Units)
Average Temperature
Compensation Error
Above 20 °C *
(°C)
8202BN
0.04
0.03
0.000
0.000
8203BN
0.04
0.01
0.000
0.000
8235BN
0.07
0.06
0.001
0.001
8256BN
0.04
0.06
0.000
0.001
8272BN
0.02
0.01
0.000
0.000
9202BN
0.03
0.06
0.000
0.001
9203BN
0.06
0.05
0.001
0.001
9206BN
0.02
0.02
0.000
0.000
9207BN
0.07
0.07
0.001
0.001
9256BN
0.02
0.00
0.001
0.000
9272BN
0.22
0.06
0.003
0.001
* For 20 °C temperature compensation spans
Active Replacement Electrode for Electrodes Listed in Table 1 and Table 2
Obsolete Electrode Available Replacement Obsolete Electrode Available Replacement
8202BN
8102BNUWP, 8102BN
9202BN
9102BNWP
8203BN
8103BNUWP, 8103BN
9203BN
9103BNWP
8235BN
8135BNUWP, 8135BN
9206BN
9106BNWP
8256BN
8156BNUWP, 815600
9256BN
9156BNWP
8272BN
8172BNWP
9272BN
9172BNWP
Advanced pH Electrode Diagnostics using LogR Technology
Electrode Troubleshooting Using LogR Technology
Many factors affect the performance of your pH combination electrode. While the majority of
problems seen in electrode performance relate to reference issues, changes over time in the
sensing glass can negatively affect performance. These effects can be monitored using a
V
ERSA
S
TAR
meter with pH/LogR measurement module. This can save
time by helping to
identify cases where cleaning and maintenance will not be able to rejuvenate the pH electrode.
Viewing Electrode Resistance
The pH electrode bulb resistance value can be viewed on the measurement screen when LogR
is selected for the temperature source. For detailed information on selecting and calibrating
LogR temperature, refer to the
LogR Temperature
Calibration
section of this user manual.
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ERSA
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Thermo Scientific