Specifications

Section 3. CR3000 Measurement Details
When the CR3000 reverses the differential input or the excitation polarity it
delays the same settling time after the reversal as it does before the first
measurement. Thus there are two delays per channel when either RevDiff or
RevEx is used. If both RevDiff and RevEx are selected, there are four
measurement segments, positive and negative excitations with the inputs one
way and positive and negative excitations with the inputs reversed. The
CR3000 switches to the channel:
sets the excitation, delays, measures,
reverses the excitation, delays, measures,
reverses the excitation, reverses the inputs, delays, measures,
reverses the excitation, delays, measures.
Thus there are four delays per channel measured. The CR3000 processes the
measurement segments into the single value it returns for the measurement.
3.1.5 Integration
Integration is used to reduce the noise included in a measurement. The
CR3000 may use a combination of analog and digital integration.
With analog integration, the input signal is integrated for a precise period of
time. The integrated value is held for the A/D conversion. There are three
possible analog integration times 20 ms, 16.67 ms and 250 µs. The 20 ms
(1/50 second) and 16.667 ms (1/60 second) are available to integrate out the
effects of noise from 50 or 60 Hz AC power sources.
An integration time is specified as part of the measurement instruction. An
integration time of 250 selects the 250 µs integration, “_60 Hz” selects the 60
Hz rejection (16.667 ms), and “_50 Hz” selects 50 Hz rejection (20 ms).
The ±5000 mV range does not use a full integration when the “_50 Hz”
integration is selected. Instead, 50 Hz noise is rejected by averaging two of the
250 µs integration measurements that are spaced exactly one half of a 50 or 60
Hz cycle apart. The average of these measurements is stored as the result of
the measurement.
The integration specified in the measurement instruction is used for each
segment of the measurement. Thus, if reversing the differential input or
reversing the excitation is specified, there will be two integrations per channel;
if both reversals are specified, there will be four integrations.
3.2 Single Ended and Differential Voltage
Measurements
A single-ended voltage measurement is made on a single input which is
measured relative to ground. A differential measurement measures the
difference in voltage between two inputs.
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