Figure 2 Drawing Of The Measuring Cell And Optical Signal Processing - M&C PMA Series Instruction Manual

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5
1 Nitrogen-filled spheres
2 Tightening strap out of platinum
3 Small mirror
4 Wedge-shaped pole pieces
5 Projektions-LED
Figure 2 Drawing of the measuring cell and optical signal processing
The measuring cell consists of two hollow spheres 1 filled with nitrogen, which are formed into a dumbbell.
In the center of rotation of the dumbbell is a small mirror 3, which surrounds a wire loop, which is required
for the compensation procedure. The above system is fixed rotationally symmetrically in a glass tube with a
platinum strap 2 and is screwed into two pole pieces 4.
Two permanent magnets generate an inhomogeneous magnetic field. When oxygen flows in, the oxygen
molecules are drawn into the magnetic field. The field lines on the wedge-shaped pole pieces 4 are com-
pressed and the nitrogen-filled diamagnetic hollow spheres are forced out of the magnetic field. This causes
the dumbbell to rotate. The rotation motion is detected by an optical system consisting of mirror 3, projection
LED 5 and photocell 6.
When the dumbbell is pushed out of the magnetic field, the voltage of the photocell changes immediately.
The measuring amplifiers 7 and 8 generate a corresponding current which generates an electromagnetic
counter-torque via the wire loop on the dumbbell. The counter torque returns the dumbbell to its zero posi-
tion.
Each change in the oxygen concentration causes a linear proportional change in the compensation current
and can therefore be read directly as oxygen value in % O
Due to its very small stagnant volume (2 cm
fast response time (T -time) of one second for a high gas flow can be realized.
90
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4
2
3
7
6
3
) and the direct flow to the M&C measuring cell, an extremely
PMA 50 EX | 1.01.04
GAS INLET
GAS OUTLET
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9
6 Photo cell
7 Measuring amplifier
8 Measuring amplifier
9 Display
on the display 9.
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