Agilent Technologies 1100 Series, Руководство по обслуживанию

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200 1100 Series Nano Pump Service Manual
5 Introduction to the Nano Pump
For pump specifications, see “Specifications” on page 257.
How Does Compressibility Compensation Work?
The compressibility of the solvents in use will affect retention-time stability
when the back pressure in the system changes (for example, aging of column).
In order to minimize this effect, the pump provides a compressibility
compensation feature which optimizes the flow stability according to the
solvent type. The compressibility compensation is set to a default value for
each pump head independently. The compensation value for each pump head
can be changed through the user interface.
Without a compressibility compensation the following will happen during a
stroke of the first piston. The pressure in the piston chamber increases and
the volume in the chamber will be compressed depending on backpressure and
solvent type. The volume displaced into the system will be reduced by the
compressed volume.
When a compressibility compensation value for a pump head is set, the pump
processor calculates a compensation volume that depends on the system
pressure and the selected compressibility value. This compensation volume is
added to the delivery stroke of the first piston.
How Does Variable Stroke Volume Work?
Due to the compression of the pump-chamber volume each piston stroke of the
pump will generate a small pressure pulsation, influencing the flow ripple of
the pump. The amplitude of the pressure pulsation is mainly dependent on the
stroke volume and the compressibility compensation for the solvent in use.
Small stroke volumes will generate less pressure pulsations than higher stroke
volumes at same flow rates. In addition the frequency of the pressure
pulsations will be higher. This will decrease the influence of flow pulsations
on quantitative results.
In gradient mode smaller stroke volumes resulting in less flow ripple will
improve composition ripple.
The nano pump uses a processor-controlled ball screw system to drive its
pistons. The normal stroke volume is optimized for the selected flow rate.
Small flow rates use a small stroke volume while higher flow rates use a higher
stroke volume.