9.14 Pressure control
Introduction
By using the function Pressure control to regulate the run, the method can be run with
the set flow rate without the risk of method stop due to pressure alarm. If the pressure
approaches the pressure limit, for example if the sample has higher viscosity than the
buffer, the flow rate is automatically lowered. Pressure control is enabled in the manual
instructions Pumps:System flow or Pumps:Sample flow. The default setting for Pressure
Control is Off. To enable the function, set what pressure signal to use. It is recommended
to use the pre-column pressure. The instruction Advanced:Pressure control parameters
provides the P and I factors used in the regulator and can be adjusted for different
columns, see information further down.
In the Method editor, pressure control is enabled by selecting Control the flow to avoid
overpressure in the predefined phase Method settings.
Pressure control parameters
The table below describes the factors used for pressure regulation.
DescriptionParameter
Proportional component in PI pressure regulation. Reduces the
error between actual and requested target pressure, but may leave
a permanent error.
P factor
Integrating component in PI pressure regulation. Eliminates the
stationary error from the P factor, but introduces a slight instability
that may lead to oscillation in the pressure and the actual flow
rate. Set I = 0 to disable the I factor. As a general guide use a small
I factor for high pressure columns and a large I factor for low
pressure columns, see Recommended pressure control parameters,
on page 513 for more recommendations.
I factor
Sets the target value for the PI pressure regulation as a percentage
of the pressure limit. If the target pressure is too close to the
pressure limit there is a risk that a short pressure spike will trigger
the pressure alarm. The pressure limit is set in the Alarm pressure
instruction. The Alarm pressure used for pressure control depends
on the settings in the System flow instruction.
Target value
for pressure
control
512 ÄKTA avant User Manual 29035184 AE
9 Reference information
9.14 Pressure control
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