Temperature Measurements
A temperature measurement is either a resistance measurement or a
voltage measurement, converted to a temperature mathematically inside
the meter. The mathematical conversions requires the knowledge of
specific properties of specific transducer types. The conversion routines
used are compatible with ITS-90. The conversion accuracy (not including
the transducer accuracy) for each transducer type is:
RTD 0.05° C
Thermistor 0.1° C
Thermocouple 0.2° C
Errors associated with temperature measurements include all those
listed for dc Voltage and Resistance Measurements. The largest source of
error in temperature measurements is the transducer itself.
Your measurement requirements determine which temperature
transducer type to use. Each transducer type has a particular
temperature range, accuracy, and cost. Each type of transducer is
described in more detail in the following subsections. The table below
summarizes some general specifications for each type of transducer.
Use the table to help select the general type of transducer to use;
transducer manufacturers can provide you with exact specifications
for a particular transducer.
RTD Thermistor Thermocouple
Temperature Range
-200 to 850
°
C -80 to 150
°
C -210 to 1820
°
C
Measurement Type
4-wire Resistance 2-wire Resistance Voltage
Transducer
Sensitivity
≈R
0
X 0.004
°
C ≈400
W
/
°
C 6 to 60 µV/
°
C
Accuracy
0.01 to 0.1
°
C 0.1 to 1
°
C 0.5 to 5
°
C
Cost (approx)
$20.00 to $100.00 ea* $10.00 to $100.00 ea* $1.00/foot*
Durability
Fragile Fragile Rugged
*Estimated cost in U.S. Dollars
7
Chapter 7 Measurement Tutorial
Measurement Techniques and Sources of Error
263
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