Appendix
67
10.5 Digital Filtering
Standard digital filtering uses mathematical averaging
to eliminate the variant digital readings that the A/D
converter sends periodically because of external
vibration. Digital filtering does not affect the indicator
measurement rate, but does affect the settling time.
The selections from 1 to 256 reflect the number of
readings averaged per update period. When a reading
is encountered that is outside a predetermined band,
the averaging is overridden, and the display jumps
directly to the new value.
RATTLETRAP
®
digital filtering (DIGFLTR values
followed by the letters RT) uses a vibration-dampening
algorithm to provide a combination of the best features
of analog and digital filtering. The RATTLETRAP
algorithm evaluates the frequency of a repeating
vibration then derives a composite displayed weight
equal to the actual weight on the scale less the
vibration-induced flaws. It is particularly effective for
eliminating vibration effects or mechanical interference
from nearby machinery. RT selections eliminate much
more mechanical vibration than standard digital
filtering, but usually also increase settling time over
standard digital filtering.
10.5.1
DFSENS and DFTHRH Parameters
The digital filter can be used by itself to eliminate
vibration effects, but heavy filtering also increases
settling time. The DFSENS (digital filter sensitivity)
and DFTHRH (digital filter threshold) parameters can
be used to temporarily override filter averaging and
improve settling time:
•
DFSENS specifies the number of consecutive
scale readings that must fall outside the filter
threshold (DFTHRH) before digital filtering
is suspended.
•
DFTHRH sets a threshold value, in display
divisions. When a specified number of
consecutive scale readings (DFSENS) fall
outside of this threshold, digital filtering is
suspended. Set DFTHRH to NONE to turn off
the filter override.
10.5.2
Setting the Digital Filter Parameters
Fine-tuning the digital filter parameters greatly
improves indicator performance in heavy-vibration
environments. Use the following procedure to
determine vibration effects on the scale and optimize
the digital filtering configuration.
1. In setup mode, set the digital filter (DIGFLTR
parameter) to 1. Set DFTHRH to NONE.
Return indicator to normal mode.
2. Remove all weight from the scale, then watch
t h e i n d i c a t o r d i s p l a y t o d e t e r m i n e t h e
magnitude of vibration effects on the scale.
Record the weight below which all but a few
readings fall. This value is used to calculate
the DFTHRH parameter value in Step 4.
For example, if a heavy-capacity scale
produces vibration-related readings of up to
50 lb, with occasional spikes to 75 lb, record
50 lb as the threshold weight value.
3. Place the indicator in setup mode and set the
D I G F LT R p a r a m e t e r t o e l i m i n a t e t h e
v i b r a t i o n e ff e c t s o n t h e s c a l e . ( L e ave
DFTHRH set to NONE.) Find the lowest
effective value for the DIGFLTR parameter.
4. Calculate the DFTHRH parameter value by
converting the weight value recorded in Step
2 to display divisions:
threshold_weight_value / DSPDIV
In the example in Step 2, with a threshold
weight value of 50 lb and a display division
value of 5D:
50 / 5D = 10.
DFTHRH should
be set to 10DD for this example.
5. Finally, set the DFSENS parameter high
enough to ignore transient peaks. Longer
transients (typically caused by lower vibration
frequencies) will cause more consecutive
out-of-band readings, so DFSENS should be
set higher to counter low frequency transients.
Reconfigure as necessary to find the lowest
effective value for the DFSENS parameter.
10.6 Conversion Factors for Secondary Units
The IQ plus 710 has the capability to mathematically
convert a weight into many different types of units and
instantly display those results with a press of the
UNITS
key.
Secondary units can be specified on the FORMAT
menu using the SECNDR parameter, or by using EDP
commands.
•
To configure secondary units using the front
panel menus, use the Table 10-5 to find the
c o nv e r s i o n m u l t i p l i e r f o r t h e M U LT
parameter. For example, if the primary unit is
pounds and the secondary unit is short tons,
set the MULT parameter to 0.000500.
•
To configure secondary units using EDP
commands, use the Table 10-5 to find the
conversion multiplier for the SEC.MULT
command. For example, if the primary unit is
pounds and the secondary unit is short tons,
s e n d t h e E D P c o m m a n d S E C . M U LT =
0.0005<CR> to set the multiplier for the
secondary units.
