50
Operation
Theory
PCI-9524
ADLINK Technology Inc.
User’s Manual
Copyright 2008
For example, a measurement device that is capable of resolving 1
in 1000 counts, can successfully register a 1-gram change on a 1-
kg capacity load-cell transducer. Consequently, a measurement
device that is capable of resolving 1 in 200,000 counts, can suc-
cessfully register a 1-gram change on a 200-kg capacity load-cell
transducer.
In practical applications, the sensitivity of load-cell transducers
vary from model to model (typically form 1 to 4mV/V), and the full-
scale output range of a transducer is usually only a fraction of the
full-scale input range of a measurement device. The convenience
of using Counts rather than Bits, is that the specified Count
achievable by a measurement device, is relative to the transduc-
ers full-scale output, rather than the full-scale input range of the
analog input amplifier. Thus, theoretically, no matter what the sen-
sitivity of the 200-kg capacity load-cell transducer you are using, a
200,000 count measurement device can always resolve a 1-gram
measurement.
Please also note, as a weight/force indicator, the displayed Counts
or Digits shall be flicker-free while the applied force is in steady
state. Therefore, a measurement device specified to have a
200,000 count resolution, must guarantee peak-to-peak system
noise and short-term drift to below 1 / 200,000, or 5-ppm of the
full-scale output range of the transducer.
The specified 200,000 count resolution capacity of PCI-9524 is
verified by a precision load-cell simulator utilizing 3mV/V sensitiv-
ity, under 10-V excitation and using a six-wire remote-sense con-
nection. The auto-zero function is enabled throughout acquisition,
while the ADC sampling rate is set to 60 samples-per-second (the
equivalent data rate is 29 samples-per-second, see Section 4.2.3
for details), and using an IIR post digital filter of 32-taps (see
Section 4.2.9 for details). Under these conditions, the peak-to-
peak system noise and drift are well below 150-nano-Volts, the
limit of 1 in 200,000 count resolution. The recording duration is 30
