Section 8. Operation
393
•
Where possible, run excitation leads and signal leads in separate shields
to minimize transients.
When measurement speed is not a prime consideration, additional time can be
used to ensure ample settling time. The settling time required can be measured
with the CR3000.
•
When relatively large resistances are measured (> 1000 ohms), or
relatively long cable lengths are used (> 50 feet) with sensors requiring
current excitation, a 0.1 µf feed-forward capacitor should be placed
between the IX and IXR to prevent excessive ringing
(p. 553).
With this
capacitor present, a minimum of 3 ms is recommended for the
SettlingTime parameter in the measurement instruction. The capacitor
simply connects between the IX terminal and the IXR terminal. The
capacitor has no polarity.
•
In difficult cases, settling error can be measured as described in
Measuring Settling Time
(p. 344).
Measuring Settling Time
Settling time for a particular sensor and cable can be measured with the CR3000.
Programming a series of measurements with increasing settling times will yield
data that indicate at what settling time a further increase results in negligible
change in the measured voltage. The programmed settling time at this point
indicates the settling time needed for the sensor / cable combination.
CRBasic example Measuring Settling Time
(p. 344)
presents CRBasic code to help
determine settling time for a pressure transducer using a high-capacitance
semiconductor. The code consists of a series of full-bridge measurements
(BrFull()) with increasing settling times. The pressure transducer is placed in
steady-state conditions so changes in measured voltage are attributable to settling
time rather than changes in pressure. Reviewing CRBasic Programming —
Details
(p. 129)
may help in understanding the CRBasic code in the example.
The first six measurements are shown in table First Six Values of Settling Time
Data
(p. 345).
Each trace in figure Settling Time for Pressure Transducer
(p. 345)
contains all twenty PT() mV/V values (left axis) for a given record number, along
with an average value showing the measurements as percent of final reading (right
axis). The reading has settled to 99.5% of the final value by the fourteenth
measurement, which is contained in variable PT(14). This is suitable accuracy
for the application, so a settling time of 1400 µs is determined to be adequate.
Содержание CR3000 Micrologger
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Страница 200: ...Section 7 Installation 200 FIGURE 42 Running Average Frequency Response FIGURE 43 Running Average Signal Attenuation ...
Страница 485: ...Section 8 Operation 485 8 11 2 Data Display FIGURE 110 Keyboard and Display Displaying Data ...
Страница 487: ...Section 8 Operation 487 FIGURE 112 CR1000KD Real Time Custom ...
Страница 488: ...Section 8 Operation 488 8 11 2 3 Final Storage Data FIGURE 113 Keyboard and Display Final Storage Data ...
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