Keysight DAQ970A User Guide

your application. The transducer manufacturers can provide you with exact specifications for a particular
transducer.
Parameter Thermocouple RTD Thermistor
Temperature Range -210 °C to 1820 °C -200 °C to 850 °C -80 °C to 150 °C
Measurement Type Voltage 2- or 4- Wire Ohms 2- or 4- Wire Ohms
Transducer Sensitivity 6 µV/°C to 60 µV/°C ≈ R
0
× 0.004 °C ≈ 400 Ω/°C
Probe Accuracy 0.5 °C to 5 °C 0.01 °C to 0.1 °C 0.1 °C to 1 °C
Cost (U.S. Dollars) $1/foot $20 to $100 each $10 to $100 each
Durability Rugged Fragile Fragile
RTDMeasurements
An RTD is constructed of a metal (typically platinum) that changes resistance with a change in temperature
in a precisely known way. The internal DMM measures the resistance of the RTD and then calculates the
equivalent temperature.
An RTD has the highest stability of the temperature transducers. The output from an RTD is also very linear.
This makes an RTD a good choice for high-accuracy and long-term measurements. The DAQ970A sup-
ports RTDs with α = 0.00385 (DIN / IEC 751) using ITS-90 software conversions. “PT100” is a special label
that is sometimes used to refer to an RTD with α = 0.00385 and R
0
= 100 Ω.
The resistance of an RTDis nominal at 0 °C and is referred to as R
0
. The DAQ970A can measure RTDs with
R
0
values from 100 Ω ±1% or 1000 Ω ±1%.
You can measure RTDs using a 2-wire or 4-wire measurement method. The 4-wire method provides the
most accurate way to measure small resistances. Connection lead resistance is automatically removed
using the 4-wire method.
Thermistor Measurements
A thermistor is constructed of materials that non-linearly changes resistance with changes in temperature.
The internal DMM measures the resistance of the thermistor and then calculates the equivalent tem-
perature.
Thermistors have a higher sensitivity than thermocouples or RTDs. This makes a thermistor a good choice
when measuring very small changes in temperature. Thermistors are, however, very non-linear, especially at
high temperatures and function best below 100 °C.
Because of their high resistance, thermistors can be measured using a 2-wire measurement method. The
internal DMM supports 2.2 kΩ (44004), 5 kΩ (44007), and 10 kΩ (44006) thermistors. The thermistor con-
version routines used by the DAQ970A are compatible with the International Temperature Scale of 1990
(ITS-90).
Thermocouple Measurements
A thermocouple converts temperature to voltage. When two wires composed of dissimilar metals are
joined, a voltage is generated. The voltage is a function of the junction temperature and the types of metals
in the thermocouple wire. Since the temperature characteristics of many dissimilar metals are well known, a
Keysight DAQ970A User's Guide 185
4Measurement Tutorials

Keysight DAQ970A Specifications

General

Scan Rate	Up to 450 channels/sec
Connectivity	USB, LAN, GPIB (optional)
Display	4.3-inch color LCD
Operating Temperature	0 °C to 50 °C
Number of slots	3 slots
Measurement Types	DCV, ACV, DCI, ACI, 2-wire resistance, 4-wire resistance, frequency, temperature, capacitance
Voltmeter	6.5 digit
Resolution	22 bits
Memory	Non-volatile memory