National Instruments PCI-6238 User Manual page 7

Contents
Chapter 4
Analog Input
Analog Input Circuitry .................................................................................................. 4-1
Analog Input Range....................................................................................................... 4-2
Connecting Analog Current Input Signals .................................................................... 4-3
Method 1 ......................................................................................................... 4-3
Method 2 ......................................................................................................... 4-4
Analog Input Ground-Reference Settings ..................................................................... 4-5
Multichannel Scanning Considerations......................................................................... 4-8
Use Short High-Quality Cabling..................................................................... 4-8
Minimize Current Step between Adjacent Channels ...................................... 4-8
Avoid Scanning Faster Than Necessary ......................................................... 4-9
Analog Input Data Acquisition Methods....................................................................... 4-10
Software-Timed Acquisitions ......................................................................... 4-10
Hardware-Timed Acquisitions ........................................................................ 4-10
Analog Input Triggering................................................................................................ 4-11
Field Wiring Considerations.......................................................................................... 4-11
Analog Input Timing Signals ........................................................................................ 4-12
AI Sample Clock Signal.................................................................................. 4-15
AI Sample Clock Timebase Signal ................................................................. 4-17
AI Convert Clock Signal................................................................................. 4-18
AI Convert Clock Timebase Signal ................................................................ 4-21
AI Hold Complete Event Signal ..................................................................... 4-21
AI Start Trigger Signal.................................................................................... 4-22
AI Reference Trigger Signal ........................................................................... 4-23
NI 6238/6239 User Manual
Configuring AI Ground-Reference Settings in Software ................. 4-7
Example 1 ......................................................................................... 4-9
Example 2 ......................................................................................... 4-9
Buffered ............................................................................................ 4-10
Non-Buffered.................................................................................... 4-11
Using an Internal Source .................................................................. 4-16
Using an External Source ................................................................. 4-16
Routing AI Sample Clock Signal to an Output Terminal................. 4-16
Other Timing Requirements ............................................................. 4-17
Using an Internal Source .................................................................. 4-18
Using an External Source ................................................................. 4-19
Routing AI Convert Clock Signal to an Output Terminal................ 4-19
Using a Delay from Sample Clock to Convert Clock ...................... 4-19
Other Timing Requirements ............................................................. 4-20
Using a Digital Source...................................................................... 4-22
Routing AI Start Trigger to an Output Terminal .............................. 4-22
Using a Digital Source...................................................................... 4-24
Routing AI Reference Trigger Signal to an Output Terminal .......... 4-24
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