Campbell-scientific CR3000 Micrologger Manual de usuario descargar pdf (Pagina 281)

100

101

Section 8. Operation

281

instructions BrFull(), BrFull6W(), BrHalf4W(), TCDiff(), VoltDiff () and

Resistance () instructions instructions perform DIFF voltage measurements.

Figure 88: PGI amplifier

A PGIA processes the difference between the H and L inputs, while rejecting

voltages that are common to both inputs. Figure PGIA with Input Signal

Decomposition

(p. 281), illustrates the PGIA with the input signal decomposed into a

common-mode voltage (V

) and a DIFF-mode voltage (V

). The common-mode

voltage is the average of the voltages on the V

and V

inputs, i.e., V

= (V

)/2, which can be viewed as the voltage remaining on the H and L inputs with

the DIFF voltage (V

) equal to 0. The total voltage on the H and L inputs is

given as V

= V

+ V

/2, and V

= V

– V

/2, respectively.

Figure 89: PGIA with input signal decomposition

8.1.2.1 Input Limits

The input limits specification is the voltage range, relative to CR3000 ground,

which both H and L input voltages must be within to be processed correctly by the

PGIA. Input limits for the CR3000 are ±5 Vdc. Input voltages in which V

or V

are beyond the ±5 Vdc input limits may suffer from undetected measurement

errors. The term “common-mode range”, which defines the valid range of

common-mode voltages, is often used instead of “input limits.” For DIFF voltages

that are small compared to the input limits, common-mode range is essentially

equivalent to input limits. Yet from figure PGIA with Input Signal Decomposition

(p. 281),

Common‐ModeRange=±5Vdc–|V

/2|,

indicating a reduction in common-mode range for increasing DIFF signal

amplitudes. For example, with a 5000 mV DIFF signal, the common-mode range

1 2 ... 276 277 278 279 280 281 282 283 284 285 286 ... 589 590

Comentarios a estos manuales

Sin comentarios

Campbell-scientific CR3000 Micrologger Manual de usuario Pagina 281

Comentarios a estos manuales

Relacionado con productos y manuales para Instrumentos de medición Campbell-scientific CR3000 Micrologger