Campbell CR800 Specifikace stáhnout pdf (Strana 78)

Section 3. CR800 Measurement Details

3-4

When the CR800 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

CR800 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 CR800 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 CR800

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 ±2500 and ±5000 mV ranges do not have the 16.667 and 20 ms

integrations. On these ranges the “_50 Hz” and “_60 Hz” integrations reject

50 or 60 Hz noise 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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Campbell CR800 Specifikace Strana 78