VTI Instruments EX1629 - Section 3 Basic Operation

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EX1629 Basic Operation 43
SECTION 3
BASIC OPERATION
INTRODUCTION
This section expands on the description of the EX1629’s features and explains how to best use
them.
ENGINEERING UNIT (EU) CONVERSION
Each EX1629 input channel can be individually configured for one of eleven different preset,
standard EU conversions. Each of these conversions is described below. Setting a specific
conversion not only controls the mathematical operations applied to the acquisition data, but also
automatically configures elements of the signal conditioning path. For example, setting a quarter-
bridge 350 conversion enables the 350 Ω completion resistor and connects the back-half resistors
to the +Sense measurement line, as illustrated in Figure 2-3. The automatic configuration,
however, can be overridden, as these elements can be configured independently.
Common terms used in the conversion equations are the following:
ε = strain
V
backhalf
= the voltage sensed from the back-half resistor network
V
-sense
= the voltage sensed on the –Sense input pin
V
+sense
= the voltage sensed on the +Sense input pin
V
unstrained
= the unstrained voltage (measured or manually entered)
V
excitation
= the excitation voltage (measured or manually entered)
GF = gage factor
ν = Poisson ratio
Quarter-Bridge 350, Quarter-Bridge 120, Quarter-Bridge User
These conversions apply to the following bridge configuration:
R
comp
R ( )
g
V
OUT
V
EXC
+
–
+
–
R
R
FIGURE 3-1: QUARTER-BRIDGE CONFIGURATION
The specific conversion is selected to match the nominal resistance of the active gage.