Hummingbird Communications Paracube Micro, Инструкция по эксплуатации

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4 of 35 01115009A _9
Paracube
®
Micro – Instruction Manual
2 Hummingbird Paramagnetic Measurement Principle
The sensor utilises the paramagnetic susceptibility of oxygen, a physical property
which distinguishes oxygen from most other common gases.
The sensor incorporates two nitrogen-filled glass spheres mounted on a strong, noble
metal taut-band suspension. This assembly, termed the ‘Suspension Assembly’ is
suspended in a symmetrical non-uniform magnetic field. When the surrounding gas
contains paramagnetic oxygen, the glass spheres are pushed further away from the
strongest part of the magnetic field. The strength of the torque acting on the
suspension is proportional to the oxygen content of the surrounding gases.
Fig.1
The measuring system is ‘null-balanced’. The 'zero' position of the suspension
assembly, as measured in nitrogen, is sensed by a differential photo-sensor assembly
that receives light reflected from a mirror attached to the suspension assembly. The
output from the photo-sensor is processed and then fed back to a coil wound around
the suspension assembly to achieve a ‘null balanced’ position. This feedback achieves
two objectives:
When oxygen is introduced to the cell, the torque acting upon the suspension
assembly is balanced by a restoring torque due to the feedback current in the coil. The
feedback current is directly proportional to the volume magnetic susceptibility of the
sample gas and hence, after calibration, to the partial pressure of oxygen in the
sample. A voltage output is derived which is proportional to the feedback current.
Taut Band
Permanent
Magnet
N2 filled
Spheres
Magnetic Field