Campbell CR3000 Micrologger, Operator'S Manual

Page: 402 / 644

Section 8. Operation
402
Analog Voltage Measurement Offsets
Differential
Measurement
With Input Reversal
Differential
Measurement
Without Input
Reversal
Single-Ended
1.5 • Basic Reso
1.0
µ
V
3 • Basic Reso
2.0
µ
V
3 • Basic Reso
3.0
µ
V
Note — the value for Basic Resolution is found in the table Analog Voltage
Measurement Resolution
(p. 352).
Analog Voltage Measurement Resolution
Input
Voltage Range
(mV)
Differential
Measurement
With Input Reversal
(
µ
V)
Basic Resolution
(
µ
V)
±
5000
83.33 167
±
1000 16.67 33.4
±
200
3.33 6.67
±
50
0.83 1.67
±
20
0.33 0.67
Note — see Specifications
(p. 95)
for a complete tabulation of measurement
resolution
As an example, figure Voltage Measurement Accuracy Band Example
(p. 354)
shows changes in accuracy as input voltage changes on the ±1000 and ±5000
input ranges. Percent-of-reading is the principle component, so accuracy
improves as input voltage decreases. Offset is small, but could be significant in
applications wherein the sensor-signal voltage is very small, such as is
encountered with thermocouples.
Offset depends on measurement type and voltage-input range. Offsets equations
are tabulated in table Analog Voltage Measurement Offsets
(p. 352).
For example,
for a differential measurement with input reversal on the ±5000 mV input range,
the offset voltage is calculated as follows:
offset
= 1.5 • Basic Reso 1.0 µV
= (1.5 • 83.33 µV) + 1.0 µV
= 126 µV
where Basic Resolution is taken from the table Analog Voltage Measurement
Resolution
(p. 352).