Campbell CR3000 Micrologger, Operator'S Manual

Page: 381 / 644

Section 8. Operation
381
The CR6 has fixed input ranges for voltage measurements and an auto-range to
automatically determine the appropriate input voltage range for a given
measurement. The table Analog Voltage Input Ranges and Options
(p. 381)
lists
these input ranges and codes.
An approximate 9% range overhead exists on fixed input voltage ranges. In
other words, over-range on the
±
1000 mV input range occurs at approximately
1090 mV and –1090 mV. The CR3000 indicates a measurement over-range by
returning a NAN (not a number) for the measurement.
Automatic Range Finding
For signals that do not fluctuate too rapidly, range argument AutoRange allows
the CR3000 to automatically choose the voltage range. AutoRange makes two
measurements. The first measurement determines the range to use. It is made
with a 250 µs integration on the ±5000 mV range. The second measurement is
made using the range determined from the first. Both measurements use the
settling time entered in the SettlingTime parameter. Auto-ranging optimizes
resolution but takes longer than a measurement on a fixed range because of the
two-measurement sequences.
An auto-ranged measurement will return NAN ("not a number") if the voltage
exceeds the range picked by the first measurement. To avoid problems with a
signal on the edge of a range, AutoRange selects the next larger range when the
signal exceeds 90% of a range.
Use auto-ranging for a signal that occasionally exceeds a particular range, for
example, a type-J thermocouple measuring a temperature usually less than 476
°
C
(
±
20 mV range) but occasionally as high as 500
°
C (
±
50 mV range). AutoRange
should not be used for rapidly fluctuating signals, particularly signals traversing
multiple voltage ranges rapidly. The possibility exists that the signal can change
ranges between the internal range check and the actual measurement.
Analog Voltage Input Ranges and Options
Range Code Description
mV5000
1
measures voltages between ±5000
mV
mV1000
2
measures voltages between ±1000
mV
mV200
2
measures voltages between ±200 mV
mV50
2
measures voltages between ±50 mV
mV20
2
measures voltages between ±20 mV
AutoRange
datalogger determines the most
suitable range
1
Append with C to enable common-mode null / open-input detect and set
excitation to full-scale DAC (~2700 mV) (Example: mV5000C)