Campbell CR3000 Micrologger, Руководство оператора

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Section 8. Operation
384
Voltage measurements are made using a successive approximation A-to-D
(p. 529)
converter to achieve a resolution of 16 bits. Prior to the A-to-D, a high
impedance programmable-gain instrumentation amplifier (PGIA) amplifies the
signal. See figure Programmable Gain Input Amplifier (PGIA)
(p. 384).
The
CRBasic program controls amplifier gain and configuration — either single-ended
input or differential input. Internal multiplexers route individual terminals to the
PGIA.
Timing
(p. 160)
of measurement tasks is precisely controlled. The measurement
schedule is determined at compile time and loaded into memory.
Using two different voltage-measurement instructions with the same voltage
range takes about twice as long as using one instruction with two repetitions.
See table Parameters That Control Measurement Sequence and Timing
(p. 385).
FIGURE 90: Programmable Gain Input Amplifier (PGIA):
H to V+, L to V–, VH to V+, VL to V– correspond to
text.
A voltage measurement proceeds as follows:
1. Set PGIA gain for the voltage range selected with the CRBasic measurement
instruction parameter Range.
2. Turn on excitation to the level selected with ExmV.
3. Multiplex selected terminals (InChan) to the PGIA and delay for the entered
settling time (SettlingTime).
4. Integrate the signal (see Measurement Integration
(p. 385)
) and perform the A-
to-D conversion.
5. Repeat for excitation reversal and input reversal as determined by parameters
RevEx and RevDiff.
6. Apply multitplier (Mult) and offset (Offset) to measured result.
See Basic Voltage Measurements — Specifications for measurement speeds.
The CR3000 measures analog voltage by integrating the input signal for a fixed
duration and then holding the integrated value during the successive
approximation analog-to-digital (A-to-D) conversion. The CR3000 can make and