3 AFC, APC
3.4
3.
36
GC-2010 Plus
3.4 AFC and APC control
3.4.1 AFC Control
AFC Control is illustrated in the following sections.
∗1. When WBI or OCI Injection is used, do not select Split mode or Splitless mode.
3.4.2 Split mode: “SPLIT” (AFC)
The AFC controls the total flow rate to keep it at a constant value. The TFC (Total Flow
Controller) inside the AFC feeds back output from the column inlet pressure sensor, which
controls the ESC (Electronic Split Controller), which, in turn, controls the column inlet
pressure.
Fig.3.4.1 shows the control status with a split ratio of 1 : 40, a velocity of 30 cm/sec, a purge
flow rate of 3 ml/min, and a column oven temperature of 50 °C.
The column inlet pressure is calculated based on the linear velocity, the oven temperature,
the column inner diameter, and the column length, and is automatically set to 49.6 kPa. In
the same way, the column flow rate is automatically set to 1.67 ml/min, and the total flow rate
is set to 69.8 ml/min (= 1.67 ml/min × 40 + 3 ml/min (= purge flow rate)).
When the Control mode is set to “PRESS”, the column inlet pressure is controlled to remain
at 49.6 kPa regardless of the column oven temperature.
When the Control mode is set to “VELOCITY”, the column inlet pressure is set to a value
which keeps the linear velocity constant despite changes in the column oven temperature.
Even if the column oven temperature changes, as in programmed temperature analysis, the
linear velocity is always kept constant. Generally, when the column oven temperature
increases, the viscosity of the carrier gas also increases, and does not flow as easily.
Regardless of the Control mode, the ESC controls the column inlet pressure and the TFC
controls the total flow rate as shown in Fig. 3.4.1.
Split mode
Control mode
Split Splitless DIRECT
(∗1)
Pressure Section 3.4.2 Section 3.4.3 Section 3.4.4
Flow rate
―― ――
Section 3.4.4
Linear velocity Section 3.4.2 Section 3.4.3 Section 3.4.4
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