| 摘要 |
1,164,344. Control of centrifuges. BECKMAN INSTRUMENTS, Inc. 24 May, 1967 [29 July, 1966], No. 24042/67. Heading B2P. [Also in Divisions G1 and H2] A centrifuge having changeable rotors of different speed ratings is associated with an overspeed shutdown system in which a signal having a frequency proportional to rotor speed is compared with a standard frequency signal. A filter responds to a predetermined minimum difference frequency signal to provide a shutdown trigger signal. The rotor is fitted with a disc having alternate reflective and non- reflective sectors co-operating with a light source and a photo-transistor 17 connected to a limiter amplifier 18, comprising a breakdown diode D1, for producing a periodic waveform related to the speed of the rotor. Limiter 18 is coupled to an overspeed demodulator 19 comprising transistor Q1 which also receives a standard frequency signal from an oscillator, comprising transistors Q3, Q4, connected to quartz crystal 22 and to a frequency divider including transistors Q5, Q6. A low pass filter 23 responds to a predetermined minimum difference frequence from the demodulator 19 to'actuate a silicon controlled rectifier 24 for shutting down the centrifuge. An auxiliary acceleration circuit (not shown) produces initial rotation of the centrifuge, a signal from amplifier 18 energising a demodulator 20, comprising transistor Q2, so that relay 29 closes the circuit of the driving motor provided that the circuit components are functioning properly. As the rotor approaches full speed, the difference frequence has a high value and the filter 23 has no output. If the speed becomes excessive, however, the filter senses a low difference frequency to actuate the rectifier 24, so earthing the collector of transistor 33 and shutting down the drive system. |
