Logr Temperature Calibration (Ph/Logr Module Only) - Thermo Scientific Orion Versa Star Pro User Manual

Thermo Scientific

LogR Temperature Calibration (pH/LogR Module Only)

The Versa Star Pro meter with pH/LogR measurement module offers the option for temperature
calibration of a pH electrode, allowing most standard glass-bulb pH electrodes to be used for
automatic temperature compensation. The type and quality of pH electrode used to perform
LogR temperature measurements will contribute to the overall temperature accuracy of the
system. To maximize LogR performance and accuracy, a Thermo Scientific™ Orion™ ROSS
Ultra™ or Thermo Scientific™ Orion™ ROSS™ pH electrode is recommended.
LogR technology is based on using the electrical resistance of a pH electrode's 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.
LogR Temperature Calibration Recommendations

When using the meter for the first time or restarting the meter in the LogR temperature
mode, a LogR temperature calibration must be performed. A LogR temperature calibration
should be performed at least once per week to ensure accurate temperature compensation
when using the LogR temperature mode. Recalibrate the LogR temperature if the meter is
disconnected from the power supply or the pH electrode is disconnected from the meter.

Up to a three point LogR temperature calibration can be performed. It is recommended that
at least two calibration points be used to meet optimum system accuracy.

Choose a temperature calibration range that is 5°C to 20°C apart, depending on the
expected sample temperature range, and evenly bracket the expected temperature range.
For example, if sample temperatures are around 25°C, calibrate at 15°C and 35°C. For
sample temperatures that differ by more than 20°C, a three point LogR temperature
calibration is recommended. For many samples, a one point LogR calibration near the
expected sample temperature will yield adequate results.

A constant temperature bath or a hot plate is recommended to hold the temperature of the
calibrating solution.

For best results during temperature calibration, it is recommended that a pH buffer or tap
water be used as the temperature calibrating solution. Do not use distilled water because
the conductivity is too low to obtain a good temperature calibration.

LogR temperature calibration can be performed using a NIST-traceable thermometer or
ATC probe. The most accurate method is to use a NIST-traceable thermometer. It is
recommended that two NIST-traceable thermometers be used to measure and verify the
temperature value. The fastest method is to use an ATC probe. If an ATC probe is
connected with the pH/LogR module when a LogR temperature calibration is performed,
the meter will import the temperature value from the ATC probe as the reference
temperature during the calibration. The temperature source used to perform the LogR
temperature calibration will contribute to the overall temperature accuracy of the system.
Detailed information on this feature is available in the

Chapter 4 pH, pH/ISE and pH/LogR Measurement Modules
Appendix section of this user manual.
Orion Versa Star Pro Meter User Manual
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