Specifications

Section 4. Sensor Support
4-10
TABLE 4.2-6. AC Noise Rejection Integration on Voltage Ranges
mV5000 and mV2500
AC Power
Line
Frequency
Measurement
Integration
Time
CRBASIC
Integration
Code
Default
Settling
Time
Maximum
Recommended
Settling Time*
60 Hz 250 μs x 2 _60Hz 3000 μs 8330 μs
50 Hz 250 μs x 2 _50Hz 3000 μs 10000 μs
*Excitation time equals settling time in measurements requiring excitation. The CR1000 cannot
excite channels Vx/EX1, Vx/EX2, and Vx/EX3 during A/D conversion. The ½ cycle technique
with excitation limits the length of recommended excitation / settling time for the first
measurement to ½ cycle. The CR1000 does not prevent or warn against setting a settling time
beyond the ½ cycle limit. For example, a settling time of up to 50000 microseconds can be
programmed, but the CR1000 will execute the measurement as follows:
1. CR1000 turns excitation on, waits 50000 microseconds, then makes the first measurement.
2. During A/D, CR1000 turns off excitation for ≈ 170 microseconds.
3. Excitation is switched on again for ½ cycle, then the second measurement is made.
Restated, a sensor does not see a continuous excitation of the length entered as the settling time
before the second measurement if the settling time entered is greater than ½ cycle. Depending on
the sensor used, a truncated second excitation may cause measurement errors.
4.2.6 Signal Settling Time
When the CR1000 switches to an analog input channel or activates excitation
for a bridge measurement, a settling time is required for the measured voltage
to settle to its true value before being measured. The rate at which the signal
settles is determined by the input settling time constant which is a function of
both the source resistance and input capacitance.
The CR1000 delays after switching to a channel to allow the input to settle
before initiating the measurement. The SettlingTime parameter of the
associated measurement instruction is provided to allow the user to tailor
measurement instructions settling times with 100 microsecond resolution.
Default settling times are listed in TABLE 4.2-7, and are meant to provide
su
fficient signal settling in most cases. Additional settling time may be
required when measuring high resistance (impedance) sensors and / or sensors
connected to the datalogger by long leads. Measurement time of a given
instruction increases with increasing settling time. For example, a 1 ms
increase in SettlingTime for a bridge instruction with input reversal and
excitation reversal results in a 4 ms increase in time for the datalogger to
perform the instruction.