VXI VT1422A, User Manual

Page: 163 / 529

Advanced Programming with the VT1529B 161 Chapter 5
Chapter 5
Advanced Programming with the VT1529B
About This Chapter
This chapter describes the advanced capability that is possible with the
VT1529B Remote Strain Conditioning Unit (RSCU). This includes being
able to scan thermocouples and high-level dc voltages in addition to strain
measurements. Also, the strain bridge excitation voltage can be included as
part of the scan list and have the VXI
plug&play driver use the updated
excitation voltage for a more accurate engineering units conversion. Using
the advanced features changes some of the VT1422A behavior and this
chapter describes these changes.
•
Additional Capabilities of the VT1529B . . . . . . . . . . . . . . . page 161
•
Changes to the Use Model . . . . . . . . . . . . . . . . . . . . . . . . . . page 162
•
Strain Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 164
-- Field Wiring for Excitation Measurements . . . . . . . . . . . . page 165
-- Strain Measurement Command Sequence . . . . . . . . . . . . page 165
-- Strain Conversion Sequence . . . . . . . . . . . . . . . . . . . . . . . page 167
-- Alternate Method of Computing Strain. . . . . . . . . . . . . . . page 168
•
Temperature Measurements . . . . . . . . . . . . . . . . . . . . . . . . . page 170
-- Connecting the VT1586A to the VT1529B . . . . . . . . . . . page 170
-- Temperature Measurement Command Sequence . . . . . . . page 174
-- Temperature Conversion Sequence. . . . . . . . . . . . . . . . . . page 175
•
Voltage Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 175
-- Field Wiring for dc Voltage Measurements . . . . . . . . . . . page 176
-- DCV Measurement Command Sequence . . . . . . . . . . . . . page 177
-- DCV Measurement Sequence . . . . . . . . . . . . . . . . . . . . . . page 178
•
Settling Time Considerations . . . . . . . . . . . . . . . . . . . . . . . . page 178
Additional Capabilities of the VT1529B
With the VT1529B/39A, only strain measurements can be made. For other
measurements, such as 1-16 V dc or thermocouple temperature
measurements, other SCPs (for example, the VT1511A Direct Input SCP or
the VT1509A Fixed Filter and Amplifier SCP) must be used. The
disadvantage of this solution is that a direct connection must be made
between the VT1422A and the sensor being measured and this can mean long
lengths of expensive shielded, twisted pair cables for each sensor, when it
would probably be prefered to make these measurements using the
VT1529A, with its 32:1 multiplexing and single cable back to the VT1422A.
Additionally, all VT1529A strain excitation voltages are measured once , when
the INITiate:IMMediate command is executed. If the excitation supply
varies over time, it is typically preferred that the excitation voltage be
measured periodically and the new values be used in the strain computation.