TriContinent C24000, Product Manual

Page: 131 / 144

Precision and accuracy
C-Series Product Manual
131
Precision and accuracy
Overview
Precision is defined as shot-to-shot repeatability. This is typically quan-
tified as “imprecision” and expressed as Coefficient of Variation (C.V.) .
The precision of the pump is mechanically controlled through a consis-
tent interface between the stepper motor/leadscrew. A correctly manu-
factured syringe has little impact on precision.
TriContinent assures precision by measuring the repeated movements of
the pump mechanism with a custom designed fixture.
Accuracy is defined as the agreement of desired volume with actual vol-
ume. The difference between the two is quantified as “inaccuracy” and
expressed as a percentage.
The accuracy of the pump is mechanically controlled through proper
leadscrew pitch and motor step angle. Correct syringe barrel I.D. also
assures accuracy. Consistency of I.D. over the entire barrel length is nec-
essary.
TriContinent assures accuracy by mechanically measuring syringe bar-
rels for proper I.D. using air bore gauges. The pump mechanism is veri-
fied by the use of manufacturing test fixtures.
When precision and accuracy data is based on results from gravimetric
testing with fluids, the test setups and environmental conditions have
been optimized. Tubing sizes, probe configurations, protocols and
speeds have been selected to provide optimum results. The fluid mea-
sured is distilled water. Whenever any of these factors are changed, you
can expect deviations from published performance data.
You can use your pump’s specifications as a benchmark to determine
how close to optimum your instrument’s fluid path is.
Performance of a liquid handling system will depend on many factors. As
a rule, empirical testing will be required to resolve all pertinent issues.
Important variables
Below are some typical variables to be considered when developing an
application-specific fluid handling system. All these items must reach a
balance before optimization is achieved.
• Syringe size , while important, is not as critical as you might imagine. A
significant shift of volume (either up or down) must be made before any
measurable difference in precision and accuracy will be noted in most
applications.
• Pump speed needs to be adjusted to deliver fluids at rates agreeable
with desired throughput but not so fast as to stall the motor when pump-
ing through restrictive tubing. It is used for “fine tuning.”
• Tubing selection can have a major impact on fluid handling performance.
Keep tubes as stiff and as short as possible. Inside diameters should be
as large as possible without causing the smallest sample/air gap to break
up. See "Optimizing tubing performance" (page 135) for more details.
• Orifices of all valves, connectors, fittings, etc. must be of appropriate size
(see tubing). Transitions must be smooth and free from unswept volume.