When evaluating a syringe
pump as part of the error
analysis of an instrument,
"accuracy" is often less
important than repeatability.
Accuracy is defined by the average amount
of fluid a syringe delivers over multiple
operations. If those individual amounts vary
widely, i.e. the precision of the the pump is
low, overall instrument error is increased.
Thus, a very "accurate" but low precision
device is much harder to control than
a device with high precision that is less
accurate. This is because, given a high level
of precision, calibration of the fluid circuit
will result in high repeatability and a reliable
instrument (see figure 5).
The bottom line is that most OEM designers
want the same action to produce the same
result reliably time after time (see figure 6),
which drives them to prioritize precision in
syringe pumps. On the other hand, accuracy
can become as important as precision for
OEMs when the goal is to establish a single
calibration to achieve dispenses of various
volumes, or a highly stable flow pattern (see
figure 7).
Conclusion
Before calibration
After calibration
Figure 5.
250
230
210
190
170
150
130
110
90
70
50
6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 7 7.1 7.2
Flow µl/min
Time (sec)
Figure 7.
1000
1200
1000
800
800
600
600
400
400
200
200
0
0
Measured (µL)
Measured (µL)
Figure 6.
actual
target
white paper 05
