National Instruments SCB-68 Chapter 4 Using Thermocouples, Chapter 5 Adding Components for Special Functions

Contents
SCB-68 Shielded Connector Block User Manual viii ni.com
Single-Ended Connection Considerations...................................................... 3-8
Single-Ended Connections for Floating Signal Sources
(RSEInput Mode) ..........................................................................3-9
Single-Ended Connections for Grounded Signal Sources
(NRSE Input Mode).......................................................................3-9
Connecting Analog Output Signals...............................................................................3-10
Connecting Digital Signals............................................................................................3-11
Connecting Timing Signals...........................................................................................3-12
Noise Considerations.....................................................................................................3-13
Chapter 4
Using Thermocouples
Switch Settings and Temperature Sensor Configuration...............................................4-2
Special Considerations..................................................................................................4-3
Chapter 5
Adding Components for Special Functions
Channel Pad Configurations..........................................................................................5-2
Conditioning Analog Input Channels............................................................. 5-2
Conditioning Analog Output Channels...........................................................5-3
Conditioning PFI0/TRIG1..............................................................................5-4
Accuracy and Resolution Considerations......................................................................5-5
Open Thermocouple Detection......................................................................................5-5
Differential Open Thermocouple Detection................................................... 5-6
Single-Ended Open Thermocouple Detection................................................ 5-6
Sources of Error..............................................................................................5-6
Lowpass Filtering..........................................................................................................5-7
Theory of Operation........................................................................................5-7
One-Pole Lowpass RC Filter..........................................................................5-10
Selecting Components.....................................................................................5-11
Adding Components.......................................................................................5-11
Single-Ended Lowpass Filter............................................................5-12
Differential Lowpass Filter...............................................................5-12
Analog Output and Digital Input Lowpass Filtering........................ 5-12
Lowpass Filtering Applications......................................................................5-13
Noise Filtering..................................................................................5-13
Antialiasing Filtering........................................................................ 5-13
Special Consideration for Analog Input Channels..........................................5-14
Special Consideration for Analog Output Signals..........................................5-14
Special Consideration for Digital Trigger Input Signals................................ 5-15
Measuring a 4 to 20mA Current ...................................................................................5-16
Theory of Operation........................................................................................5-16