Specifications

Section 4. Sensor Support
4-6
CR1000 measurement instructions incorporate techniques to cancel these
unwanted offsets. TABLE 4.2-3 lists measurement instructions and offset
v
oltage compensation options available to each.
TABLE 4.2-3. Analog Measurement Offset Voltage Compensation
CRBASIC
Voltage
Measurement
Instruction
Input
Reversal
(RevDiff = True)
Excitation
Reversal
(RevEx = True)
Measure
Ground
Reference
Offset
(MeasOff = True)
Background
Calibration
(RevDiff = False)
(RevEx = False)
(MeasOff = False)
VoltDiff() * *
VoltSe() * *
TCDiff() * *
TCSe() * *
BrHalf() * *
BrHalf3W() * *
Therm107() * *
Therm108() * *
Therm109() * *
BrHalf4W() * * *
BrFull() * * *
BrFull6W() * * *
AM25T() * * *
4.2.3.1 Input and Excitation Reversal (RevDiff, RevEx = True)
Reversing inputs (differential measurements) or reversing polarity of excitation
voltage (bridge measurements) cancels stray voltage offsets. For example, if
there is a +3 μVolt offset in the measurement circuitry, a 5 mV signal will be
measured as 5.003 mV. When the input or excitation is reversed, the
measurement will be -4.997 mV. Subtracting the second measurement from
the first and dividing by 2 cancels the offset:
5.003 mV - (-4.997 mV) = 10.000 mV
10.000 mV / 2 = 5.000 mV.
When the CR1000 reverses differential inputs or excitation polarity, it delays
the same settling time after the reversal as it does before the first measurement.
Thus there are two delays per channel when either RevDiff or RevEx is used.
If both RevDiff and RevEx are True, four measurements are performed;
positive and negative excitations with the inputs one way and positive and
negative excitations with the inputs reversed. To illustrate,
the CR1000 switches to the channel
sets the excitation, settles, measures,
reverses the excitation, settles, measures,
reverses the excitation, reverses the inputs, settles, measures,
reverses the excitation, settles, measures.