Campbell CR1000, Руководство оператора

Страница: 309 / 678

Section 8. Operation
An approximate 9% range overhead exists on fixed input voltage ranges. In other
words, over-range on the
±
2500 mV input range occurs at approximately 2725
mV and –2725 mV. The CR1000 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 CR1000 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
( ± 25 mV range) but occasionally as high as 500 ° C ( ± 250 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.
Table 55. Analog Voltage Input Ranges and Options
Range Code Description
mV5000 measures voltages between ±5000 mV
mV2500
1
measures voltages between ±2500 mV
mV250
2
measures voltages between ±250 mV
mV25
2
measures voltages between ±25 mV
mV7_5
2
measures voltages between ±7.5 mV
mV2_5
2
measures voltages between ±2.5 mV
AutoRange
3
datalogger determines the most suitable range
1
Append with C to enable common-mode null / open-input detect and set excitation to full-scale
(~2700 mV) (Example: mV2500 )
2
Append with C to enable common-mode null / open-input detect (Example: mV25C )
3
Append with C to enable common-mode null / open- input detect on ranges ≤ ±250 mV, or just
common-mode null on ranges > ±250 mV (Example: AutoRangeC )
309