Operator's Manual
Issue 14
/
Mar 2016 / UMC0071
Mercury
iPS
©2016 Oxford Instruments NanoScience. All rights reserved.
Page
67
8 Tap
Calculate
to request the iPS to do the calculations.
9 Tap
Save
to save the new calibration.
10 Tap
Home
to return to home page.
In the sequence above, tapping “Calculate” in step 5 writes the pair of values ‘measured
variable value’ and ‘Actual T1 for a T1 reference point to an internal table. Tapping “Calculate”
in step 7 does the same for a T2 reference point. Tapping “Calculate” again will perform
iterative adjustments of ‘Scale’ and ‘Offset’ to find the best small correction to fit the generic
curve to the actual reference point data with the minimum error.
6.5 Types of temperature sensor
The
Mercury
iPS can use several types of temperature sensor.
6.5.1 Thermocouples
A thermocouple comprises two junctions of dissimilar metals held at different temperatures. This
acts as a voltage source, based on the Seebeck effect, the output voltage of which increases
with increasing temperature difference. The iPS contains cold-junction compensation, so a
reference junction is not required.
6.5.2 Metallic resistance thermometers (positive temperature
coefficient)
The resistance of metallic resistors increases with increasing temperature due to the increase of
scattering events of the conduction electrons. Over much of the temperature range the
relationship is approximately linear until, at low temperatures, impurity scattering becomes
significant and the sensor sensitivity flattens off. The iPS passes a constant current through the
sensor and measures the voltage produced, using a 4-wire measurement. Resolution to 1 mK is
possible at low temperatures, if a suitable resistor and energisation current are used.
6.5.3 Semiconductor resistance thermometers (negative
temperature coefficient)
Semiconductor resistance thermometers (negative temperature coefficient)
The resistance of semiconductor resistors decreases with increasing temperature. The
