Hardy HI 1756-nDF - Manual (Page 20)

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Chapter 4
Overview of Operation
The HI 1756 nDF will calculate Gross weight, Net weight, & Flow Rate (FR) outputs
simultaneously, as shown in the simplified block diagram below.
Weigh Filter
NumAVg
Weight
Conditioning
Weight
Calculation
Weight
Value
Flow Rate
Calculation
Flow Rate Time Base
Weight Unit
Flow Rate
Filter
Flow Rate
Value
Load Cell
Signal
Flow Rate Update Period
Flow Rate Filter
Material
ADC
Weight Update Rate
Current
Flow Rate
Auto_Preact
Calculation
Auto_Preact
stable
capture time p gain
i gain
frc tolerance
variation
capture
steady period
auto preact config
start wait
fast adjust
Simplified block diagram for the 1756-1DF
Overview of Weight Calculation
The ADC data can be filtered to reduce short term disturbances caused by system noise,
vibration noise, and local short term disturbances that could affect the weigh
measurement.
The most robust method to reduce these system disturbances is Waversaver®, but this
mode has the longest delay which is directly proportional to the bandwidth selected as the
algorithm requires at least one full cycle of the lowest frequency to be able to remove the
noise and harmonics from the weight measurement. On the other hand the raw data
sample mode provides the fastest response with no additional delay but does not filter out
any noise from the sampled data. As a compromise a low pass filter can be selected to
provide noise shaping across multiple samples centered on the current weigh value; this
mode has a fixed delay of 100mS.
The filter selection will depend upon the environment and the desired response time to
changes in weight.