Campbell Scientific CR5000 Measurement and Control Module - Manual (Page 132)

Section 7. Measurement Instructions
7-6
BrHalf3W (Dest, Reps, Range, SEChan, ExChan, MeasPEx, ExmV, RevEx,
SettlingTime, Integ, Mult, Offset)
X = result w/mult = 1,
offset = 0
X
V V
V V
R
R
x
s
f
=
−
−
=
2
2 1
1
This Instruction is used to determine the ratio of the sensor resistance to a
known resistance using a separate voltage sensing wire from the sensor to
compensate for lead wire resistance.
The measurement sequence is to apply an excitation voltage and make two
voltage measurements on two adjacent single-ended channels: the first on the
reference resistor and the second on the voltage sensing wire from the sensor.
The two measurements are used to calculate the resulting value (multiplier = 1,
offset = 0) that is the ratio of the voltage across the sensor to the voltage across
the reference resistor.
BrHalf4W (Dest, Reps, Range1, Range2, DiffChan, ExChan, MeasPEx,
ExmV, RevEx, RevDiff, SettlingTime, Integ, Mult, Offset)
X = result w/mult = 1,
offset = 0
X
V
V
R
R
s
f
= = 2
1
This Instruction applies an excitation voltage and makes two differential
voltage measurements, then reverses the polarity of the excitation and repeats
the measurements. The measurements are made on sequential channels. The
result is the voltage measured on the second channel (V2) divided by the
voltage measured on the first (V1). The connections are made so that V1 is the
voltage drop across the fixed resistor (Rf), and V2 is the drop across the sensor
(Rs). The result with a multiplier of 1 and an offset of 0 is V2 / V1 which
equals Rs / Rf.