Measurement and control unit
The detector's flash lamp and spectrometer need to be synchronized to the rotor's revolutions. This task, known as multiplexing, is performed by a standalone control unit placed into the centrifuge, below the rotor chamber. It takes in all electronic connections to the operating computer and to the detector's hardware components – the lamp, the spectrometer, and the stepper motor.
Nanolytics Instruments' Omega Device is a compact hardware solution for the sake of limiting the controlling computer's actions to top level control by the operating software. All continuous tasks, such as counting the rotor's revolutions in given time intervals, flashing the lamp at given angles, and optionally multiplexing the light source of a second detector, are performed by a primitive microcomputer inside the omega device. Thus, these tasks are robust against any delays and timeouts of a Windows based personal computer.
The Omega device contains a counting unit, transmitting the current rounds per minute to the controlling PC three times a second. The runtime integral thus calculated has been shown to be more precise than in existing analytical ultracentrifuges. The angular velocity ω, critical physical property of an AUC experiment at any time, has given the device its name.
The device further contains two multiplexing units, programmed by the controlling software to initiate light flashes at a given angle, i. e. the position of the cell currently to be scanned. The device will precisely carry out these actions on a sub-millisecond time scale until notified to do otherwise. It represents an autonomous low level controlling unit.
The device also contains low level electronics for converting the rotor's hall pulses (periodic sines) into TTL rectangles needed by the computer logics. Conversion parameters can be adjusted by dials on the front panel, LEDs allow to monitor the converter's actions. Thus, the conversion can be adapted to low or high hall outputs that may be dependent on the strength of the magnet inside the rotor and the rotor-pickup distance.
Other dials and switches on the front panel allow to control the light sources' intensity or to mute them. Power supplies located inside the housing feed all detector hardware components – a single 220 V power feed is required to power the entire system. The housing provides failsafe connections to all components, acting as a general connector interface between computer and detector hardware. The clearly arranged setup simplifies troubleshooting and prevents any mixup of USB, serial, and power connections.
