224 Agilent 1200 Series Autosampler Reference Manual
7 Introduction to the Autosampler
Needle-Drive
The needle movement is driven by a stepper motor connected to the spindle
assembly by a toothed belt. The circular motion of the motor is converted to
linear motion by the drive nut on the spindle assembly. The upper and lower
needle positions are detected by reflection sensors on the sampling unit flex
board, while the needle-in-vial position is determined by counting the motor
steps from the upper needle-sensor position.
Analytical head / preparative head
The analytical head is driven by the stepper motor connected to the drive shaft
by a toothed belt. The drive nut on the spindle converts the circular movement
of the spindle to linear motion. The drive nut pushes the sapphire plunger
against the tension of the spring into the analytical head. The base of the
plunger sits on the large bearing of the drive nut, which ensures the plunger is
always centered. A ceramic ring guides the movement of the plunger in the
analytical head. The home position of the plunger is sensed by an infra-red
sensor on the sampling unit flex board, while the sample volume is determined
by counting the number of steps from the home position. The backward
movement of the plunger (driven by the spring) draws sample from the vial.
Table 38 Analytical Head Technical Data
Standard (100 µl Standard (900 µl) Preparative (900 µl)
Number of steps 15000 15000 15000
Volume resolution 7 nl/motor step 60 nl/motor step 60 nl/motor step
Maximum stroke 100 µl 900 µl 900 µl
Pressure limit 400 bars 200 bars 400 bars
Plunger material Sapphire Sapphire Sapphire
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