SHB_U14 Chapter 3: Module components 3-3
Modulator
Location in module
The modulator is attached to the main frame.
Structure
The modulator consists of:
• Receiver disk
• 1 to 2 emitter inserts
• Aperture wheel
• Synchronous motor to drive the aperture wheel
• Coupling between synchronous motor and aperture wheel
• Circuit board with
• Emitter power supply connections
• Synchronous motor connection
• Split light barrier
• O rings to seal the emitter units and the entire modulator
Function
The computer-controlled synchronous motor drives the aperture wheel.
Modulation frequencG: 7.3 Hz (standard setting).
The aperture wheel is designed to alternately cover the test and reference
chambers in the sample cell so that the infrared light from the emitters passes
alternately through each chamber twice per revolution.
The IR detector signal arrangement is assured by the split light barrier and a flag
fastened to the aperture wheel drive shaft.
This design solution creates modulated light which results in a highly stable
measurement signal.
Figure 3-3
Modulator
1 Aperture wheel
2 Synchronous motor
3 Emitter circuit board
4 Emitter inserts
5 Receiver disk
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