Thermo Scientific 5028i Instruction Manual page 223

System Description
Hardware
Measurement Head
The measurement head uses a beta source and proportional alpha/
beta detector to measure the attenuation of beta particles by sampled
aerosol across a glass fiber filter and to discriminate against any naturally
occurring beta interferences from the daughter nuclides of alpha decay
products. The Model 5028i has two measurement heads, named as
Channel A and Channel B.
Detector Amplifier
This cylindrical tube houses a printed circuit board, provides power to
the proportional detector and amplifies the beta and alpha counts prior
to being sent to the 5028i measurement interface board. The Model
5028i has two detector amplifiers, one is for Channel A, and another
one is for Channel B, each detector amplifier can work independently.
Cam Photo Interrupt Board
This small printed circuit board includes a photo-interrupter to detect
the closed position of the measurement head. This is connected to a
motor assembly used to open and close the measurement head.
Counter Wheel Interrupt
This small printed circuit board is mounted onto a chopper wheel that
measures the amount of filter tape advanced during a filter tape change.
Board Assembly
Proportional Valve
The proportional valve is a proportional solenoid valve that is used
as a means of flow control. In response to the measured flow across
a subsonic orifice, the proportional valve will either partially open or
close to make a flow adjustment in real-time. The Model 5028i has two
proportional valves use to maintain the sample flow rate at its nominal
value.
3-way Valve
The two 3-way valves on the real panel are controlled by the instrument
firmware to make it power on or power off when automatic filter tape
changes are controlled.
Cam Motor
This motor is used to drive the cam to rotate. By rotating the cam, the
measurement head lever arm is raised and lowered for opening and
closing the measurement head during a filter tape change.
Tape Motor
After the measurement head is opened, this motor is used to advance
the filter tape a fixed amount prior to initiating another beta attenuation
event on a fixed sample spot.
Thermo Fisher Scientific Model 5028i Instruction Manual 8-3