National Instruments DAQCard-1200 Types of Signal Sources

Chapter 3 Signal Connections

DAQCard-1200 User Manual 3-6 © National Instruments Corporation

The instrumentation amplifier applies gain, common-mode voltage

rejection, and high-input impedance to the analog input signals connected

to the DAQCard-1200. Signals are routed to the positive and negative

inputs of the instrumentation amplifier through input multiplexers on the

DAQCard-1200. The instrumentation amplifier converts two input signals

to a signal that is the difference between the two input signals multiplied by

the gain setting of the amplifier. The amplifier output voltage is referenced

to the DAQCard-1200 ground. The DAQCard-1200 ADC measures this

output voltage when it performs A/D conversions.

All signals must be referenced to ground, either at the source device or at

the DAQCard-1200. If you have a floating source, you must use a

ground-referenced input connection at the DAQCard-1200. If you have a

grounded source, you must use a nonreferenced input connection at the

DAQCard-1200.

Types of Signal Sources

When configuring the input mode of the DAQCard-1200 and making

signal connections, you must first determine whether the signal source is

floating or ground referenced. This section describes these two types of

signals.

Floating Signal Sources

A floating signal source is not connected in any way to the building ground

system but has an isolated ground-reference point. Some examples of

floating signal sources are outputs of transformers, thermocouples,

battery-powered devices, optical isolator outputs, and isolation amplifiers.

You must tie the ground reference of a floating signal to the

DAQCard-1200 analog input ground to establish a local or onboard

reference for the signal. Otherwise, the measured input signal varies or

appears to float. An instrument or device that supplies an isolated output

falls into the floating signal source category.

Ground-Referenced Signal Sources

A ground-referenced signal source is connected in some way to the

building system ground and is therefore already connected to a common

ground point with respect to the DAQCard-1200, assuming that the PC is

plugged into the same power system. Nonisolated outputs of instruments

and devices that plug into the building power system fall into this category.

Contents

Main Page Important Information Warranty Copyright Trademarks WARNING REGARDING USE OF NATIONAL INSTRUMENTS PRODUCTS Contents Chapter 4 Theory of Operation Page Tables About This Manual Organization of This Manual Conventions Used in This Manual National Instruments Documentation Related Documentation Introduction About the DAQCard-1200 What You Need to Get Started Software Programming Choices LabVIEW and LabWindows/CVI Application Software NI-DAQ Driver Software Register-Level Programming Optional Equipment Unpacking Installation and Configuration Installation Configuration Analog Input Configuration Analog Input Polarity Analog Input Mode RSE Input (Eight Channels, Default Setting) NRSE Input (Eight Channels) DIFF Input (Four Channels) Analog Output Configuration Analog Output Polarity Digital I/O Configuration Counter Configuration Signal Connections I/O Connector Figure 3-1. DAQCard-1200 I/O Connector Pin Assignments Signal Connection Descriptions Analog Input Signal Connections + Types of Signal Sources Floating Signal Sources Ground-Referenced Signal Sources Input Configurations Differential Connection Considerations (DIFF Configuration) Differential Connections for Grounded Signal Sources Figure 3-3. Differential Input Connections for Grounded Signal Sources Differential Connections for Floating Signal Sources Figure 3-4. Differential Input Connections for Floating Sources Single-Ended Connection Considerations Single-Ended Connections for Floating Signal Sources (RSE Configuration) Single-Ended Connections for Grounded Signal Sources (NRSE Configuration) Common-Mode Signal Rejection Considerations Analog Output Signal Connections Digital I/O Signal Connections Page Port C Pin Connections Timing Specifications Mode 1 Input Timing Mode 1 Output Timing Mode 2 Bidirectional Timing Page DAQ and General-Purpose Timing Signal Connections DAQ Timing Connections Page Page Page General-Purpose Timing Signal Connections Page Page Figure 3-18. Frequency Measurement Application Chapter 3 Signal Connections DAQCard-1200 User Manual 3-30 National Instruments Corporation Figure 3-19. General-Purpose Timing Signals The GATE and OUT signals in Figure3-19 are referenced to the rising edge of the CLK signal. Power Connections National Instruments Corporation 4-1 DAQCard-1200 User Manual Theory of Operation This chapter explains the operation of each functional unit of the DAQCard-1200. Figure 4-1. DAQCard-1200 Block Diagram Functional Overview The block diagram in Figure 4-1 shows a functional overview of the DAQCard-1200. PC Card I/O Channel Interface Circuitry Timing Chapter 4 Theory of Operation Figure 4-3. Timing Circuitry DAQCard-1200 User Manual 4-4 National Instruments Corporation Analog Input Analog Input Circuitry Page Data Acquisition Timing Data Acquisition Operation Continuous Data Acquisition Interval Data Acquisition Data Acquisition Rates Page Analog Output Analog Output Circuitry Power-On State DAC Timing Digital I/O Calibration Calibration at Higher Gains Calibration Equipment Requirements Using the Calibration Function Page A Specifications Analog Input Input Characteristics Transfer Characteristics Amplifier Characteristics Dynamic Characteristics Stability Analog Output Output Characteristics Transfer Characteristics Page Timing I/O Digital Trigger Bus Interface Power Requirement Physical Page B Differences among the Lab-PC+, the DAQPad-1200, and the DAQCard-1200 Page C Power-Management Modes Page D PC Card Questions and Answers Configuration Operation Resources Page Page E Technical Support Resources NI Web Support Online Problem-Solving and Diagnostic Resources Software-Related Resources Worldwide Support Glossary Numbers/Symbols A B C D E F G Page Page V Index Numbers A B C D E F G I L M N O R S T U V W