The signal resolution = 5mV / 1000 divisions = 5 µV/division
7.2.2 Dual Interval and Dual Range Operation
The indicator provides single range, dual interval and dual range modes. In non-trade operation, up to 100,000
divisions are available so it is rare for the precision of the displayed reading to be a problem. However in trade
applications where the number of divisions that can be legally displayed is limited, the use of dual interval
or dual range operation allows greater precision in the displayed readings without exceeding the maximum
number of graduations available in the certification of the loadcell.
Both of these modes of operation allow for the indicator to operate with 2 count-by settings so that it is possible
to weigh for example up to 2 kg in 1g increments and then up to 5kg in 2g increments.
Dual interval and dual range are identical in many respects and can be treated the same for the purposes of
setup and calibration. The difference in the two comes about in the operation of the scale. With dual range
operation the range is determined based on the gross weight. Once the scale changes from low range to high
range it will not change back to low range until the scale is returned to a stable zero reading. Dual interval
operation however is based on the net weight and no restrictions are placed on the change from the high interval
to the low interval. With dual interval operation it is therefore possible to weigh in the low interval with high
tare weights.
The indicator is equally accurate in either mode but due to hysteresis effects with many loadcells it may not be
possible to operate accurately in dual interval mode. In these cases dual range mode ensures that the weight
readings taken from the loadcell are accurately displayed during loading and unloading operations.
7.2.3 Direct mV/V Operation
It is possible to calibrate the indicator without test weights if the output capacity of the loadcell is known.
For applications like silo weighing etc where it is impractical to use test weights this mode of operation allows
the mV/V signal strength at no load, as well as the mV/V signal strength of the span to be entered directly.
This type of calibration is only as accurate as the loadcell output figures but for many applications this is more
than adequate. For more details see Section 7.6.
7.2.4 Maintenance Date
The indicator is able to indicate when it is due for recalibration or regular maintenance. This is set in CLOCK:
QA.OPT and CLOCK:QA.DATE. When the due date is reached, the indicator displays (CAL) (DUE). Pressing any
key will hide this message temporarily. This message can only be disabled by changing the QA settings (which
requires full setup).
7.2.5 Filtering Techniques
The indicator has a number of advanced filtering options which allow it to be optimized to produce the most
accurate readings possible in the shortest time. There is a trade-off between noise reduction and step response
time.
Note
The step response is the time between placing a weight on the scale and the correct
weight reading being displayed.
FIR Filter:
The first level of filtering provided is a FIR filter that is linked to the measurement rate. The measurement
rate is set in BUILD:SYNC. This filter is a very high performance ’tuned’ filter that provides up to 180 dB
of attenuation at multiples of the SYNC frequency and broad band filtering of between 40 and 80 dB
generally. For example, setting the SYNC frequency at 25Hz would provide 180 dB of noise rejection at
25, 50, 75 . . . Hz.
The primary noise source is the mains power so the SYNC is usually set to half the mains frequency or
the mains frequency. For example, with 50Hz mains power, use 12.5, 25 or 50Hz SYNC frequency. The
42 C500-600-2.0.3
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