National Instruments NI 9219 2-Wire Resistance and Quarter-Bridge Modes

© National Instruments Corp. 15 NI 9219 Operating Instructions

lead wires have the same resistance. A gain of 2x is applied to the

voltage across the negative lead wire and the ADC uses this voltage

as the negative reference to cancel the resistance error across the

positive lead wire. Refer to Figure8 for an illustration of the

connections.

Figure 8. Connections in 3-Wire RTD Mode

2-Wire Resistance and Quarter-Bridge Modes

In 2-Wire Resistance and Quarter-Bridge modes, connect the

twoends of the resistor or gauge to the NI 9219 across the HI and

LO terminals. These modes source a current, which varies based on

the resistance of the load, between the HI and LO terminals. The

resulting resistance is computed from the voltage measurement.

2-Wire Resistance and Quarter-Bridge modes do not compensate

LO

EX+

EX–

RTD

Wire

Wire

Wire

I

x2

ADC

I

I

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