7.2.1.1
BrHalf4W()
The
BrHalf4W()
CRBasic instruction is used to measure the TempVue 10 in a 4-wire
configuration. It applies an excitation voltage and makes two differential voltage measurements.
The first measurement is made across the fixed resistor (Rf), the second is made across the RTD
(Rs). The result is the ratio of the two resistances (Rs/Rf), which is not affected by cable length.
The
BrHalf4W()
instruction has the following form:
BrHalf4W
(Dest, Reps, Range1, Range2, DiffChan, ExChan, MeasPEx, ExmV, RevEx,
RevDiff, SettlingTime, fN1, Mult, Offset)
Use the DUT value for the
Offset
. The DUT value is included on the calibration sheet and is
unique to each sensor. Campbell Scientific recommends using a 50000 µsec
SettlingTime
.
Refer to
(p. 18) if in electrically noisy environments.
7.2.1.2
BrHalf()
The
BrHalf()
CRBasic instruction is used to measure the 2-wire configuration. It applies an
excitation voltage, delays a specified amount of time, and then makes a single ended voltage
measurement.
The
BrHalf()
instruction has the following form:
BrHalf
(Dest, Reps, Range, SEChan, ExChan, MeasPEx, EXmV, RevEx, SettlingTime, fN1,
Mult, Offset)
Campbell Scientific recommends using a 50000 µsec
SettlingTime
. For the
Offset
, use a
TempVue 10 calibration from a third party accredited laboratory.
For the 2-wire configuration, before the resistance value is converted to temperature, the
CRBasic program needs to calculate the Rs/R0 ratio. To do this, include the following:
'Calculate the value of Rs
Rs = Rf*X/(1-X)
'Calculate the ratio of Rs/R0
TempVue10RsR0 = Rs/R0
Where,
Rf = 10100 (the resistance of Rf)
R0 = 100 (the resistance of the PRT at 0 °C)
X= the
Dest
variable that stores the
BrHalf()
measurement. Refer to
(p. 24) for more information.
TempVue 10 PT-100 Class A, Precision Air Temperature Sensor
12
