Ohmart Vega W-4510, Техническое руководство по аппаратному обеспечению

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Setup
W-4510 Weigh Scale Technical Reference Manual 73
Filtering
This feature enables change to the response time of the system by increasing or decreasing
the averaging time that the gauge uses to filter the noise in the signal. An increased time for
averaging enables the accumulation of a greater number of readings and therefore produces
a greater statistical accuracy. However, this is at the expense of response time to changes in
the process.
Type (RC exponential or rectangular window)
The W-4510 offers a choice of signal filters such as
•
Linear
•
RC exponential
•
Rectangular window
The W-4510 transmitter has a sample rate of about one sample/second, but process
variables generally change measurably on the order of minutes. Electrical and source noise
occur on the order of seconds, so they can be filtered out with a low pass filter, leaving only
the change in the process variable in the signal.
RC exponential
RC exponential filtering simulates the traditional Resistance/Capacitance filtering. It provides
an infinite impulse, in which all of the previous samples contribute less and less to the
average, but all contribute somewhat. The most recent samples are weighted most heavily in
computing the average. Compared to rectangular window filtering, RC exponential filtering
provides a quicker response to step changes in the process but has a larger noise band.
Rectangular window filtering
Rectangular window filtering computes an average based only on a specified (finite) number
of samples. All samples are weighted equally in the average. Although it provides a slower
step response (since the most recent measurements are weighted the same as those further
back in time), it produces a less noisy signal. Generally, rectangular window linear averaging
by itself produces results similar to combining RC exponential filtering with the fast cutoff
feature.
Diagnostic RC filter
The measurement channel has either a rectangular or diagnostic RC filter. When you point
this filter to a specific address, it will display the filtered counts. For example, you can point to
address 2814 (raw counts) and 2810 (seconds). Screen 2812 then displays the filter count
number.