Campbell Scientific CR6 CR6 Measurement and Control System - Page 330

BrHalf3W, BrHalf4W, BrFull6W, Table 72., Resistive-Bridge Circuits with Voltage Excitation

Page 330 highlights

Section 8. Operation labeled Rf are normally precision fixed (static) resistors. CRBasic example FourWire Full-Bridge Measurement (p. 334) lists CRBasic code that measures and processes four-wire full-bridge circuits. Offset voltages are a part of bridge measurements as they are of simpler analogvoltage measurements. In addition to RevDiff and MeasOff parameters discussed in the section Offset Voltage (p. 323), CRBasic bridge measurement instructions include the RevEx parameter that provides the option to program a second set of measurements with the excitation polarity reversed. Much of the offset error inherent in bridge measurements is canceled out by setting RevDiff, MeasOff, and RevEx to True. Measurement speed can be slowed when using RevDiff, MeasOff, and RevEx .When more than one measurement per sensor are necessary, such as occur with the BrHalf3W(), BrHalf4W(), and BrFull6W instructions, input and excitation reversal are applied separately to each measurement. For example, in the fourwire half-bridge (BrHalf4W()), when excitation is reversed, the differential measurement of the voltage drop across the sensor is made with excitation at both polarities and then excitation is again applied and reversed for the measurement of the voltage drop across the fixed resistor. Further, the result of measurement instructions is X, which often must be processed further to obtain the resistance value, requiring additional processing time. Table 72. Resistive-Bridge Circuits with Voltage Excitation Resistive-Bridge Type and Circuit Diagram Half-Bridge1 CRBasic Instruction and Fundamental Relationship CRBasic Instruction: BrHalf() Fundamental Relationship2: Other Relationships 330

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Section 8.
Operation
labeled R
f
are normally precision fixed (static) resistors.
CRBasic example
Four-
Wire Full-Bridge Measurement
(p. 334)
lists CRBasic code that measures and
processes four-wire full-bridge circuits.
Offset voltages are a part of bridge measurements as they are of simpler analog-
voltage measurements.
In addition to
RevDiff
and
MeasOff
parameters discussed
in the section
Offset Voltage
(p. 323),
CRBasic bridge measurement instructions
include the
RevEx
parameter that provides the option to program a second set of
measurements with the excitation polarity reversed.
Much of the offset error
inherent in bridge measurements is canceled out by setting
RevDiff
,
MeasOff
, and
RevEx
to
True
.
Measurement speed can be slowed when using
RevDiff
,
MeasOff
, and
RevEx
.When more than one measurement per sensor are necessary, such as occur with
the
BrHalf3W()
,
BrHalf4W()
, and
BrFull6W
instructions, input and excitation
reversal are applied separately to each measurement.
For example, in the four-
wire half-bridge (
BrHalf4W()
), when excitation is reversed, the differential
measurement of the voltage drop across the sensor is made with excitation at both
polarities and then excitation is again applied and reversed for the measurement of
the voltage drop across the fixed resistor.
Further, the result of measurement
instructions is X, which often must be processed further to obtain the resistance
value, requiring additional processing time.
Table 72.
Resistive-Bridge Circuits with Voltage Excitation
Resistive-Bridge Type and
Circuit Diagram
CRBasic Instruction and
Fundamental Relationship
Other
Relationships
Half-Bridge
1
CRBasic Instruction:
BrHalf()
Fundamental Relationship
2
:
330