34410A/11A/L4411A User’s Guide 115
Measurement Tutorial 4
Temperature Measurements
The multimeter allows the measurement of temperature by measurement of
the temperature sensitive resistance of two different "Probe" types: the
resistance temperature detector (RTD) of 0.00385/
o
C; and thermistors of
2.2 KΩ, 5 KΩ, or 10 KΩ). There are a number of measurement parameter and
technique choices available to you, and these affect various aspects of the
measurement:
• Temperature range and resolution can direct the probe–type choice.
• Choice of four–wire or two–wire technique affects measurement accuracy.
• Use of the auto zero feature affects measurement speed and accuracy.
• Choice of integration (measurement time) setting affects measurement
accuracy and power–line noise rejection.
• Use of the offset compensation feature can eliminate residual voltages in
the test instrumentation or circuit.
Probe Type Choice
RTD's provide very accurate, highly linear relationships between resistance
and temperature, over a range of roughly –200 to 500
o
C. There is very little
conversion complexity for an RTD since it is so intrinsically linear. The
multimeter provides measurement for the IEC751 standard RTD, which has a
sensitivity of 0.00385/
o
C.
Thermistors consist of semiconductor materials, and provide roughly
10 times the sensitivity of the RTD. Because they are semiconductors, their
temperature range is more limited, commonly to –80
o
C to 150
o
C.
Thermistors have highly non–linear temperature–resistance relationships;
therefore their conversion algorithms are more complex. The Agilent
multimeters use the standard Hart–Steinhart Approximation to provide
accurate conversions, with a typical resolution of 0.08
o
C.
2–Wire vs. 4–Wire Measurements
As with resistance measurements, four–wire temperature measurements are
more accurate, since errors due to lead wire resistance are completely
eliminated. Alternately, you can use the multimeter’s Null function to remove
the test lead resistance from the measurement (see “NULL Reading:” on
page 116).
UG_ED5.book Page 115 Thursday, March 1, 2012 11:28 AM
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