Network Card User Manual
Table Of Contents
- SCXI-1121 User Manual
- Support
- Important Information
- Contents
- About This Manual
- Chapter 1 Introduction
- Chapter 2 Configuration and Installation
- Chapter 3 Theory of Operation
- Chapter 4 Register Descriptions
- Chapter 5 Programming
- Appendix A Specifications
- Appendix B Rear Signal Connector
- Appendix C SCXIbus Connector
- Appendix D SCXI-1121 Front Connector
- Appendix E SCXI-1121 Cabling
- Appendix F Revision A and B Photo and Parts Locator Diagrams
- Appendix G Technical Support Resources
- Glossary
- Index
- Figures
- Figure 2-1. SCXI-1121 General Parts Locator Diagram
- Figure 2-2. SCXI-1121 Detailed Parts Locator Diagram
- Figure 2-3. SCXI-1121 Front Connector Pin Assignment
- Figure 2-4. Ground-Referenced Signal Connection with High Common-Mode Voltage
- Figure 2-5. Floating Signal Connection Referenced to Chassis Ground for Better Signal-to-Noise Ratio
- Figure 2-6. Floating AC-Coupled Signal Connection
- Figure 2-7. AC-Coupled Signal Connection with High Common-Mode Voltage
- Figure 2-8. Assembling and Mounting the SCXI-1330 Connector-and-Shell Assembly
- Figure 2-9. Nulling Circuit
- Figure 2-10. Shunt Circuit
- Figure 2-11. SCXI-1320 Parts Locator Diagram
- Figure 2-12. SCXI-1328 Parts Locator Diagram
- Figure 2-13. SCXI-1321 Parts Locator Diagram
- Figure 2-14. SCXI-1121 Rear Signal Connector Pin Assignment
- Figure 2-15. SCANCLK Timing Requirements
- Figure 2-16. Slot-Select Timing Diagram
- Figure 2-17. Serial Data Timing Diagram
- Figure 2-18. Configuration Register Write Timing Diagram
- Figure 2-19. SCXI-1121 Module ID Register Timing Diagram
- Figure 3-1. SCXI-1121 Block Diagram
- Figure 3-2. SCXIbus Connector Pin Assignment
- Figure 3-3. Digital Interface Circuitry Block Diagram
- Figure 3-4. SCXI-1121 Digital Control
- Figure 3-5. Analog Input Block Diagram
- Figure 3-6. Analog Output Circuitry
- Figure 3-7. Single-Module Parallel Scanning
- Figure 3-8. Single-Module Multiplexed Scanning (Direct)
- Figure 3-9. Single-Module Multiplexed Scanning (Indirect)
- Figure 3-10. Multiple-Module Multiplexed Scanning
- Figure 3-11. Multiple-Chassis Scanning
- Figure B-1. SCXI-1121 Rear Signal Connector Pin Assignment
- Figure C-1. SCXIbus Connector Pin Assignment
- Figure D-1. SCXI-1121 Front Connector Pin Assignment
- Figure E-1. SCXI-1340 Installation
- Figure E-2. SCXI-1180 Rear Connections
- Figure E-3. SCXI-1180 Front Panel Installation
- Figure E-4. Cover Removal
- Figure F-1. Revision A and B SCXI-1121 Signal Conditioning Module
- Figure F-2. Revision A and B SCXI-1121 General Parts Locator Diagram
- Figure F-3. Revision A and B SCXI-1121 Detailed Parts Locator Diagram
- Tables
- Table 2-1. Digital Signal Connections, Jumper Settings
- Table 2-2. Jumper W33 Settings
- Table 2-3. Gain Jumper Allocation
- Table 2-4. Gain Jumper Positions
- Table 2-5. Filter Jumper Allocation
- Table 2-6. Voltage and Current Mode Excitation Jumper Setup
- Table 2-7. Maximum Load per Excitation Channel
- Table 2-8. Excitation Level Jumper Selection
- Table 2-9. Completion Network Jumpers
- Table 2-10. Trimmer Potentiometer and Corresponding Channel
- Table 2-11. Nulling Resistors and Corresponding Channel
- Table 2-12. Jumper Settings of the Nulling Circuits
- Table 2-13. Jumper Settings on the SCXI-1320 Terminal Block
- Table 2-14. Jumper Settings on the SCXI-1328 Terminal Block
- Table 2-15. Jumper Settings on the SCXI-1321 Terminal Block
- Table 2-16. SCXIbus to SCXI-1121 Rear Signal Connector to Data Acquisition Board Pin Equivalences
- Table 3-1. SCXIbus Equivalents for the Rear Signal Connector
- Table 3-2. Calibration Potentiometer Reference Designators
- Table 5-1. SCXI-1121 Rear Signal Connector Pin Equivalences
- Table E-1. SCXI-1121 and MIO-16 Pinout Equivalences
- Table E-2. SCXI-1341 and SCXI-1344 Pin Translations
- Table E-3. SCXI-1342 Pin Translations
- Table E-4. SCXI-1343 Pin Connections
Chapter 3 Theory of Operation
SCXI-1121 User Manual 3-10 www.natinst.com
The analog input consists of four isolated single-ended noninverting
amplifiers. In addition, lowpass filtering is available at the inputs. You can
jumper select one of two bandwidths, 10 kHz or 4 Hz. The amplifier gain
is divided into two stages, a first stage providing gains of 1, 10, 50, and 100,
and a second stage providing gains of 1, 2, 5, 10, and 20. Also, the module
has an internal completion network that can be used with half-bridge or
quarter-bridge networks. Each channel is configurable to a different
bandwidth, gain, or completion network operation.
Use the following formula to determine the overall gain of a given amplifier
input channel:
where G
total
is the overall gain and G
1st
and G
2nd
are the first and
second-stage gains. It is important to note that the choice of gain in each
stage will affect the amplifier bandwidth. To determine the bandwidth of a
given gain stage use the following formula:
where BW is a given amplifier stage bandwidth, GBWP is the gain
bandwidth product (typically 800 kHz), and G is the gain at this stage. This
BW might be of concern at high first-stage gains such as 50 and 100. In this
case the first-stage amplifier has a BW equal to 16 kHz and 8 kHz,
respectively. Because of this decrease in the amplifier bandwidth, the
channel overall bandwidth decreases, but noise immunity improves. If this
bandwidth limitation is unacceptable, you should spread the gains over
both stages, thus increasing the BW of each amplifier stage. In most cases
this will introduce a negligible effect on the channel bandwidth. For
example, to achieve a gain of 100, use G
1st
= 10 and G
2nd
= 10 for a gain of
1,000 use G
1st
= 50 and G
2nd
= 20.
All the amplifier input channels are overvoltage-protected to 240 V
rms
with
power on or off.
The isolated amplifiers fulfill two purposes on the SCXI-1121 module.
They convert a small signal riding on a high common-mode voltage into a
single-ended signal with respect to the SCXI-1121 chassis ground. With
this conversion, the input analog signal can be extracted from a high
common-mode voltage or noise before being sampled and converted by the
data acquisition board. The isolated amplifier also amplifies and conditions
an input signal, which results in an increase in measurement resolution and
accuracy.
G
total
G
1st
G
2nd
×=
BW
GBWP
G
-----------------=