7.2.9 Calculate Zero Correction = tc (ph - pc) - pc
th - tc
7.2.10 Place sensor in cold bath. Stir and wait until sensor reading on display
stabilizes. Note reading and then adjust “Zero” control potentiometer
marked (R13) so that the zero correction calculated in step 8.2.9. above is
added to or subtracted from the sensor reading. If the answer in step 8.2.9
above is positive, add the correction, if negative, subtract.
7.2.11 Now place thermometer in the cold bath with the sensor and stir. Now
adjust the “span” potentiometer until the two reading are equal (the
displayed reading, and the reading of reference thermometer).
7.2.12 Check readings in hot bath. Slight touch-up of “Span” control may be
required. Normally not more than a ±0.1 degrees correction is necessary if
the calculated measure “Cold” temperature procedure has been performed
correctly.
The above method allows the operator to perform the calibration in one
step. If desired, and particularly if the error is minor, an adjustment of
zero may be performed in the cold bath to equal the thermometer reading.
Then the span may be adjusted in the hot bath. However, this procedure
requires repetition until both cold and hot bath readings are correct without
further adjustment in either cold or hot baths.
Page 13
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