Digital Filtering; Theory Of Operation; Setting Filtering Controls - Rice Lake IQ plus 310A Installation Manual

7.2 DIGITAL FILTERING

7.2.1 PRINCIPLES OF OPERATION
The IQ plus 310A uses an averaging digital filter to reduce the effect of vibration on weight
readings. Adjustable threshold and sensitivity functions allow quick settling by temporarily
cutting out averaging so the reading immediately jumps to the new value being received.
There are three filtering controls—averaging (DFILT), a cutout threshold (DF THRH), and a
cutout sensitivity (DF SENS).
The averaging controls (DFILT 1—DFILT 3) are tunable cascaded stages controlling the
effect that a single A/D reading has on the current displayed weight. By default, DFILT 2
and DFILT 3 will acquire the same setting as DFILT 1 unless they are individually set to
different values.
• A setting of OFF for all three stages disables all averaging. It produces a 1-in-1
effect, so the current A/D reading is simply the displayed weight (1 x 1 x 1).
• An intermediate setting, for example 8, 8, 8, produces an averaging effect such that
each A/D reading has a 1-in-512 effect on the displayed weight (8 x 8 x 8).
• A setting of 256 for all three stages produces the heaviest averaging. At that level,
each A/D reading has less than a 1-in-16 million effect on the current displayed
weight (256 x 256 x 256).
This averaging function (DFILT 1—DFILT 3) can be used by itself to eliminate the effects of
vibration, but heavy digital filter averaging significantly increases the settling time. To over-
come this, the DF THRH (Digital Filtering Threshold) and DF SENS (Digital Filtering Sensi-
tivity) controls can be used to temporarily override (cutout) averaging. You specify a thresh-
old (in display divisions) and a sensitivity "n" (in numbers of readings) to set the cutout
point.
• If "n" consecutive readings are beyond the threshold, filtering will cutout, or be
disabled, until the scale has settled. (Note that because vibration may not allow the
scale to go to standstill while filtering is disabled, the settling detection is not the
same as motion detection. The scale may still be "in motion" when filtering is re-
enabled).

7.2.2 SETTING FILTERING CONTROLS

To set filtering controls, first determine the maximum vibration effects present by running
DFILT 1—3 with no filtering (OFF, OFF, OFF) and an empty scale (or displaying a zero
net). Watch the display and record the number below which all but a few of the variations
fall. Convert this weight reading to display divisions (maximum weight reading divided by
your display division size — 1, 2, or 5 — equals total display divisions caused by vibration).
You will use this number of display divisions when setting the final cutout threshold (DF
THRH). Just record the number for now, leaving the DF THRH set to NONE.
With the DF THRH level set to NONE, adjust the three averaging controls (DFILT 1—3) to
eliminate the effects of vibration on the readings. Set these as low as possible. Higher
settings will increase the settling time in the vicinity of the target weight.
Next set the filter cutout level (DF THRH) using the value you calculated above.
Next set the cutout sensitivity value (DF SENS) high enough to ignore transient peaks. The
longer the duration of the peaks (typically, the lower the vibration frequency), the higher the
sensitivity setting should be. Setting this value higher increases the settling time when a
weight is added to the scale, as it increases the time before the cutout is engaged.
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