Specifications

Section 4. Sensor Support
4-4
4.2.2 Voltage Range
In general, a voltage measurement should use the smallest fixed input range
that will accommodate the full scale output of the sensor being measured. This
results in the best measurement accuracy and resolution. The CR1000 has six
fixed input ranges for voltage measurements, along with an autorange option
that enables the CR1000 to automatically determine the appropriate input
voltage range for a given measurement. TABLE 4.2-2 describes the CR1000
i
nput voltage range options along with the associated alphanumeric range
codes.
TABLE 4.2-2. Analog Voltage Input Ranges with Options for Open Input
Detect (OID) and Pull into Common Mode (PCM).
Range Code Description
mV5000
1
measures voltages between +5000 mV
mV2500
2
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 OID/PCM and set excitation to full-scale DAC (~2700 mV)
2
Append with “C” to enable OID/PCM
3
Append with “C” to enable OID/PCM on ranges ≤ +250 mV, PCM on ranges > +250 mV
Fixed Voltage Ranges
As listed in TABLE 4.2-2, the CR1000 has six fixed input ranges for voltage
measu
rement. An approximately 9% range overhead exists on all input voltage
ranges. For example, 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.
AutoRange
For signals that do not fluctuate too rapidly, AutoRange allows the CR1000 to
automatically choose the voltage range to use. AutoRange makes two
measurements. The first measurement determines the range to use, and is made
with the 250 μs integration on the ±5000 mV range. The second measurement
is made using the appropriate range with the integration specified in the
instruction. Both measurements use the settling time programmed in the
instruction. AutoRange optimizes resolution but takes longer than a
measurement on a fixed range, because of the two measurements required.
An AutoRange 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.