National Instruments NI PCI-6110, NI PCI-6111 Differential Measurements

Chapter 4 Connecting Signals

NI PCI-6110/6111 User Manual 4-10 ni.com

Differential Measurements

The following sections discuss the use of differential (DIFF) measurements

and considerations for measuring both floating and ground-referenced

signal sources.

Table4-4 summarizes the recommended DIFF signal connections and

includes input examples for both types of signal sources.

Differential Connection Considerations

A differential connection is one in which the NI PCI-6110/6111 AI signal

has its own reference signal or signal return path. The device channels are

always configured in DIFF input mode. The input signal is tied to the

positive input of the PGIA, and its reference signal, or return, is tied to the

negative input of the PGIA.

Each differential signal uses two inputs—one for the signal and one for its

reference signal.

Differential signal connections reduce noise pickup and increase

common-mode noise rejection. Differential signal connections also allow

input signals to float within the common-mode limits of the PGIA.

Table 4-4. Signal Source Types

DIFF Input

Examples and

Signal Source

Floating Signal Source

(Not Connected to Building Ground) Grounded Signal Source

Input Examples • Ungrounded thermocouples

• Signal conditioning with isolated

outputs

• Battery devices

• Plug-in cards with nonisolated

outputs

Differential

(DIFF)

See text for information on bias resistors.

+

–

+

–

ACH0(+)

ACH0(–)

ACH0GND

V

1

+

–

+

–

ACH0(+)

ACH0(–)

ACH0GND

V

1

Contents

Main Page Important Information Warranty Copyright Trademarks Patents Compliance FCC/Canada Radio Frequency Interference Compliance Determining FCC Class FCC/DOC Warnings Class A Contents Chapter 4 Connecting Signals Page About This Manual Conventions National Instruments Documentation Related Documentation Introduction About the NI PCI-6110/6111 What You Need to Get Started Software Programming Choices NI-DAQ National Instruments ADE Software Optional Equipment Custom Cabling Unpacking Safety Information Page Page Installing and Configuring the NI PCI-6110/6111 Installing the Software Installing the Hardware Configuring the Device National Instruments Corporation 3-1 NI PCI-6110/6111 User Manual Hardware Overview DAQ - STC RTSI Bus Figure 3-1. NI PCI-6110 Block Diagram I/O Connector Analog Input Input Mode Note The inputs are differential only in the sense that the ground loops are broken. The I/O Connector RTSI Bus Input Polarity and Input Range Considerations for Selecting Input Ranges Input Coupling Analog Output Analog Trigger Figure 3-3. Analog Trigger Block Diagram for the NI PCI-6110 Figure 3-4. Analog Trigger Block Diagram for the NI PCI-6111 Page Page Digital I/O Timing Signal Routing Page Programmable Function Inputs Device and RTSI Clocks RTSI Triggers Connecting Signals I/O Connector Figure 4-1. 68-Pin I/O Connector Pin Assignment for the NI PCI-6110/6111 Figure 4-2. 50-Pin Connector Pin Assignments for the NI PCI-61 10/6111 I/O Connector Signal Descriptions Table 4-2. Signal Descriptions for I/O Connector Pins Page Page Table 4-3. I/O Signal Summary for the NI PCI-6110/6111 Table 4-3. I/O Signal Summary for the NI PCI-6110/6111 (Continued) Connecting Analog Input Signals Types of Signal Sources Floating Signal Sources Ground-Referenced Signal Sources Differential Measurements Differential Connection Considerations Differential Connections for Ground-Referenced Signal Sources Figure 4-4. Differential Input Connections for G round-Referenced Signals Differential Connections for Nonreferenced or Floating Signal Sources Common-Mode Signal Rejection Considerations Working Voltage Range Analog Output Signal Connections Digital I/O Signal Connections Power Connections Timing Connections Programmable Function Input Connections DAQ Timing Connections TRIG1 Signal TRIG2 Signal Page STARTSCAN Signal Page CONVERT* Signal AIGATE Signal SISOURCE Signal SCANCLK Signal EXTSTROBE* Signal Waveform Generation Timing Connections WFTRIG Signal UPDATE* Signal UISOURCE Signal General-Purpose Timing Signal Connections GPCTR0_SOURCE Signal GPCTR0_GATE Signal GPCTR0_OUT Signal GPCTR0_UP_DOWN Signal GPCTR1_SOURCE Signal GPCTR1_GATE Signal GPCTR1_OUT Signal GPCTR1_UP_DOWN Signal Page FREQ_OUT Signal Field Wiring Considerations Page Calibration Loading Calibration Constants Self-Calibration External Calibration A Specifications Analog Input Input Characteristics Accuracy Information Transfer Characteristics Amplifier Characteristics Dynamic Characteristics Stability Analog Output Output Characteristics Transfer Characteristics Voltage Output Dynamic Characteristics Stability Digital I/O Timing I/O General-Purpose Up/Down Counter/Timers Frequency Scaler Triggers Analog Trigger Digital Trigger External Input for Digital or Analog Trigger (PFI0/TRIG1) Page Environmental Safety Electromagnetic Compatibility CE Compliance Page Figure B-1. 68-Pin Connector Pin Assignment for the NI PCI-611 0/6111 Figure B-2. 50-Pin Connector Pin Assignment for the NI PCI-611 0/6111 C Common Questions General Information Installing and Configuring Analog Input and Output Timing and Digital I/O Page Page D Technical Support and Professional Services Page Glossary Numbers/Symbols A B C D E F G H I K L M N O P Page R S T U V W Index Symbols Numerics A B C D E F G H I K L M N O Q R S T U V W