National Instruments NI PXI-4224 Common-Mode Rejection Ratio

Chapter 4 Theory of Operation

NI PXI-4224 User Manual 4-4 ni.com

Figure 4-2. Effect of Input Impedance on Signal Measurements

Although RS does not influence DC measurements, take care when

measuring AC signals since CIN attenuates higher frequencies if RS is too

large. For example:

Common-Mode Rejection Ratio

The ability of a measurement device to reject voltages that are common to

both input terminals is referred to as the common-mode rejection ratio

(CMRR). The CMMR is usually stated in decibels at a given frequency or

over a given frequency band of interest. Common-mode signals can arise

from a variety of sources and can be induced through conductive or

radiated means. One of the most common sources of common-mode

interference is 50 or 60 Hz powerline noise.

The minimum NI PXI-4224 CMRR is 140 dB, which results in a reduction

of CMV by a factor of 10,000,000.

V

SIG

+

–

+

–

Measured

Voltage

V

MEAS

Input

Impedance

Source

Impedance

R

IN

R

S

Signal Source

C

IN

100

pF

VMEAS

VSIGRIN

RSRIN

+

--------------------=

Bandwidth 1

2πRSCIN

----------------------=

Contents

Main Page Important Information Warranty Copyright Trademarks Patents Conventions Contents Page Figures Tables About the NI PXI-4224 What You Need to Get Started National Instruments Documentation Installing the Application Software, NI-DAQ, and the DAQ Device Installing the NI PXI-4224 LED Pattern Descriptions Connecting Signals Connecting Signals to the NI PXI-4224 Front Signal Connector Page Analog Input Connections Page Figure 2-3. Unshielded Grounded Signal Source Connection Using a D-SUB Connector Figure 2-4. Shielded Floating Signal Source Connection Using a D-SUB Connector Figure 2-5. Shielded Grounded Signal Source Connection Using a D-SUB Connector Figures 2-6 through 2-9 illustrate connecting signals using a terminal block. Figure 2-6. Unshielded Floating Signal Source Connection Using a Terminal Block Figure 2-7. Unshielded Grounded Signal Source Connection Using a Terminal Block Figure 2-8. Shielded Floating Signal Source Connection Using a Terminal Block Floating Signal Source Connection Ground-Referenced Signal Connection Shielded Ground-Referenced Signal Connection (Recommended) Configuring and Testing Verifying and Self-Testing the Signals Using Test Panels Configuring the NI PXI-4224 in MAX Creating a Voltage Task or Global Channel Using NI-DAQmx Verifying and Self-Testing an NI-DAQmx Task or Global Channel Page Chapter 4 Theory of Operation Figure 4-1. Block Diagram of NI PXI-4224 NI PXI-4224 User Manual 4-2 ni.com Signal Conditioning Functional Overview Measurement Considerations Input Impedance Common-Mode Rejection Ratio Effective CMR Timing and Control Functional Overview Programmable Function Inputs Device and PXI Clocks Figure 4-4 shows this signal connection scheme. Figure 4-4. NI PXI-4224 PXI Trigger Bus Signal Connection Page Using the NI PXI-4224 Developing Your Application Typical Program Flow Chart Figure 5-1. Typical Program Flowchart Overview of Typical Flow Chart Creating a Task Using DAQ Assistant or Programmatically Adjusting Timing and Triggering Configuring Channel Properties Acquiring, Analyzing, and Presenting Completing the Application Developing an Application Using LabVIEW Page Using a DAQmx Channel Property Node in LabVIEW Synchronization and Triggering Synchronizing the NI PXI-4224 Figure 5-2. General Synchronizing Flowchart Synchronizing the NI PXI-4224 Using LabVIEW Other Application Documentation and Material Calibrating the NI PXI-4224 Loading Calibration Constants Self-Calibration External Calibration A Specifications Overvoltage Protection Analog Input Accuracy Transfer Characteristics Calibration Pre-Calibration Errors Memory Digital Triggers PXI Trigger Bus PCI Bus Interface Power Requirements Physical Maximum Working Voltage Isolation Voltages Environmental Safety Electromagnetic Compatibility CE Compliance Online Product Certification Environmental Management RoHS B Timing Signal Information Connecting Timing Signals Programmable Function Input Connections DAQ Timing Connections AI START TRIG Signal AI REF TRIG Signal AI SAMP CLK Signal Page AI CONV CLK Signal AI PAUSE TRIG Signal AI SAMPLE CLK TIMEBASE Signal AI HOLD COMPLETE Signal C Removing the NI PXI-4224 Removing the NI PXI-4224 from a PXI or PXI/SCXI Combination Chassis Removing the NI PXI-4224 from MAX D Common Questions Page Glossary Symbols A B C D E F G H I K L M N O P R S T V Page Index A B C D E F G H I L O P Q R S T V