Temperature Measurements

The NI 4065/4070/4071/4072 can measure temperature using common temperature transducers. The three most commonly used transducers for temperature are thermocouples, resistance temperature detectors (RTDs), and thermistors. Compatible thermocouples and RTDs are available from National Instruments and compatible thermistors are available from Omega.

The following table illustrates some of the capabilities and limitations of these sensors. Use this table as a reference for choosing the right sensor for your temperature measurement application.

Sensor	Advantages	Disadvantages
Thermocouples	wide range, fast response, inexpensive	require reference temperature, nonlinear
RTDs	rugged, accurate	slow response, lead resistance, nonlinear, self-heating
Thermistors	repeatable, fine resolution, low current, fast response	narrow range, nonlinear

The following table lists NI-DMM supported device/sensor combinations:

Device	Thermocouple Support	RTD Support	Thermistor Support
NI 4070/4071/4072/4065	2-wire ITS-90 polynomial scaling Presets for types J, K, N, T, E, R, S, and B	4-wire and 2-wire Callendar-Van Dusen scaling Presets for common sensor standards (alpha=0.00385, alpha=0.00391, etc.) Custom coefficients	2-wire Stein-Hart scaling Presets for common Omega 44000 Series thermistors (44004, 44006, 44007) Custom coefficients

Measurement Range, Resolution, and Options

NI-DMMs perform a measurement appropriate to the temperature transducer type (DC voltage for thermocouples, resistance for RTDs or thermistors), and convert this reading into degrees Celsius. See thermocouples, RTDs, and thermistors for specific cabling details.

When configuring a temperature transducer measurement, the user must specify the range and resolution of the underlying voltage or resistance measurement while configuring the DMM. The following range settings are recommended for optimal accuracy, speed, and range of the supported transducers. Users may wish to select a different range for measurements at extreme temperatures or when using custom transducer types.

Transducer	Recommended Range
Thermocouple	100 mV
100 Ω RTD	1 kΩ
1k Ω RTD	10 kΩ
1kΩ to 10kΩ Thermistor	100 kΩ

Other measurement options, such as Auto Zero, Offset Compensated Ohms, Settling Time, and Aperture Time still apply to the underlying voltage or resistance measurement where applicable.