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RUSKA 7750i
Users Manual
As pressure is applied in the helical tube, the entire apparatus attempts to rotate. This
causes the mirror to move the reflected light spot to shine more on one photodiode than
the other. The Sensor Board (see Chapter 2, Sensor Board section) then responds by
changing the current to the electromagnetic coils that, through interaction with the
permanent magnets, force the helical tube to return to its zero position. The amount of
current required to do this is proportional to the pressure applied across the helical tube.
Thus, the pressure is determined by the amount of current required to return the helical
tube to its zero position.
On the Absolute Ps sensor, the process is similar, except that the Bourdon tube is
permanently evacuated and sealed at the factory, and the test pressure is applied to the
sensor case. With this configuration, all test pressures are measured with respect to
vacuum.
ELECTROMAGNETIC
PERMANENT
MAGNET
POTENTIOMETER FOR ZERO
2-8
TORSION HINGE
COIL
SHIFTING LIGHT SPOT,
SHOWN AT NULL POSITIO
BETWEEN PHOTOCELL
PHOTOCELL
S GENERATE
VOLTAGE ACORDING TO
ILLUMINATION
-ADJUST
CALIBRATION OF THE QBT GAUG
Figure 2-4. Photocell/Light Spot
PHOTOCELLS
ERROR SIGNAL TO CONTR
AMPLIFIER IS ZERO WHE
PHOTOCELLS ARE EQUAL
ILLUMINATED
FUSED QUARTZ BOURDON
TUBE ASSEMBLY
MIRROR
TORSION HINGE
BEAM OF LIGHT,
REFLECTED BY
PIVOTING MIRROR
LED LIGHT SOURCE
gme05.eps
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