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National Instruments NI 9219 4-Wire Resistance and 4-Wire RTD Modes, 3-Wire RTD Mode

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NI 9219 Operating Instructions 14 ni.com

4-Wire Resistance and 4-Wire RTD Modes

4-Wire Resistance and 4-Wire RTD modes source a current, which

varies based on the resistance of the load, between the EX+ and

EX– terminals. The measured resistance is computed from the

resulting voltage reading. These modes are not affected by lead

wire resistance because a negligible amount of current flows across

the HI and LO terminals due to the high input impedance of the

ADC. Refer to Figure7 for an illustration of the connections.

Figure 7. Connections in 4-Wire Resistance and 4-Wire RTD Modes

3-Wire RTD Mode

3-Wire RTD mode sources a current, which varies based on the

resistance of the load, between the EX+ and EX– terminals. This

mode compensates for lead wire resistance in hardware if all the

LO

HI

EX–

RTD/

Resistor

Wire

Wire

Wire

I

ADC

I

EX+

Wire

NI 9219

Contents

Main Safety Guidelines Safety Guidelines for Hazardous Voltages Safety Guidelines for Hazardous Locations Special Conditions for Marine Applications Wiring the NI 9219 Page Page Connecting Wires to the NI 9219 Connectors Wiring TEDS Channels Grounding and Shielding Considerations Figure 3. Connecting a Grounded Signal Source to the NI 9219 Figure 4. Connecting a Floating Signal Source to the NI 9219 NI 9219 Timing Options NI 9219 Circuitry Figure 5. Input Circuitry for One Channel Voltage and Current Modes Figure 6. Connections in Voltage, Current, and Digital In Modes + 4-Wire Resistance and 4-Wire RTD Modes 3-Wire RTD Mode 2-Wire Resistance and Quarter-Bridge Modes Half-Bridge and Full-Bridge Modes Thermocouple Mode Digital In Mode Open Contact Mode Sleep Mode Binary Data Excitation Protection Specifications Input Characteristics Page Page Page Page Input noise in ppm of Range Page Page Power Requirements Physical Characteristics Safety Safety Voltages Safety Standards Hazardous Locations Environmental Shock and Vibration Electromagnetic Compatibility CE Compliance Waste Electrical and Electronic Equipment (WEEE) Calibration Where to Go for Support