Centrifuge 5804/5804 R and 5810/5810 R
10 Descriptions
10-4 Descriptions
Rotational speed monitoring and rotor recognition
These functions are carried out with the help of a unipolar Hall sensor with an open-collector output. A
"pull-up" resistor (R32) in the output of the sensor is used as a load resistor which supplies a defined
signal at the processor input if e.g. a cable break occurs between the sensor and the PCB “58xx
Control“. The Hall sensor (HAL506UA) is soldered to a sensor board which is located underneath the
motor covering in the rotor chamber.
Under the influence of the magnetic field of the coded magnet bar in the lower part of the rotor the
output of the sensor becomes conductive against ground. The sensor board is connected to the control
PCB via the plug connector X10. The pulses are supplied via a triggered inverter (IC5) at PORT 1.3 and
1.4 of the processor.
During the rotation the magnetic strips on the rotor move past the Hall sensor and according to the
length of the strips they generate “LOW“ pulses which are analyzed as rotational speed pulses. The
magnetic systems of the rotors consist of a strip with even length (starting magnet) and a strip with
variable length which enables coding of the rotors. By making the relation, a large number of rotors can
be coded. The rotational speed has no influence in this context. R23 and C38 serve to reduce interfering
pulses (low-pass filter) and IC 5 serves to improve the pulse steepness.
For measuring purposes the rotational speed pulses can be taken from OUTX(X17).
Imbalance monitoring
The imbalance monitoring is done by a system which analyzes the distance between a magnet fastened
to the motor and a Hall sensor which is installed in a fixed position on the motor plate. This sensor is an
analogue Hall sensor (UGN3503U) in which a voltage is induced that corresponds to the strength and
polarity of the magnetic field. This voltage is applied to the A/D converter in the processor (PORT 7.3).
Depending on the position of the motor the magnetic field of the magnet influences the sensor with
different field strengths which in turn changes the induced voltage at the output.
The voltage is proportional to the deflection. This enables an analysis of the imbalance that can be
exactly reproduced. An RC combination (R14, C31) serves as a low-pass filter that dampens interfering
pulses.
The sensor is integrated on the PCB "Imbalance detection" which amplifies the Hall signal. This
assembly group is installed at a distance of approx. 10 mm from the initial magnet.
In order to achieve a sufficient signal the operating voltage of the OpAmp. on the imbalance PCB is 8 V.
The signal is generated on the control PCB from the 24V supply by means of a Z stabilization.
Since the analogue voltage at the processor input to be analyzed may not exceed 5 V, the voltage is
limited by a 4.7 V Z-diode (D2).
MSTM/KW/0408
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