PS081 datasheet(40/155 Pages) AMSCO

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3-17

PSØ81

3.5.3.2

Stretched Single Conversion Mode

Figure 3.19 Stretched single conversion mode

For mechanically sensitive weigh scales like kitchen scales the PS081 provides the stretched mode

combined with the single conversion mode. In this mode the two resistors of a half bridge are mea-

sured subsequently, but the next pair of discharge time measurements follows delayed. Therefore,

the sample points of a single sequence can cover minimum a full period of the mechanical oscillation.

Thanks to the integration of the samples within one sequence the result will normally be stable if the

break is <30% of the time.

Figure 3.20 Undersampling

Again, the oscillator is switched on only for each discharge time measurement. But, as the oscillator

needs some time to reach the full amplitude, the total active time of the oscillator is longer than for

pure Single Conversion Mode. The current consumption in stretched single conversion mode is there-

fore a little bit increased compared to the single conversion mode.

Four major parameters define the operation mode:

single_conversion:

Selects between continuous operation and single separated measurements.

stretch:

Selects between 4 MHz oscillator continuously running while measuring and

running the oscillator only for the duration of 1 or 2 discharge cycles (recom

mended 2 discharge cycles)

cycletime:

Defines the time interval between single or pairs of discharge cycles. It is

based on the 4 MHz clock or in stretched mode on the 10 kHz clock.

avrate:

Sample size of averaging. Defines the number of complete ratio measure

ments that make a single measurement sequence (internal averaging).

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