Drive motor timers

The electrical system provides power for the operation of the fan motor, the gear motor and magnetic clutches in the reversing drive, the timer motor, and the air solenoid valve. The manually initiated timer was adjustable for processing times up to 15 min. 

The speed of a centrifuge should be checked at least once every 3 months. The procedure should use a stroboscopic light or a vibrating-reed external tachometer of known accuracy. The measured speed should not differ by more than 5% from the rated speed under specified conditions. All the speeds at which the centrifuge is commonly operated should be checked. The centrifuge timer should be checked weekly against a reference timer (such as a stopwatch) and should not be more than 10% in error. Commutators and brushes should be checked at least every 3 months. Brushes (where used) should be replaced when they show considerable wear. However, in many modern induction-drive motors, brushes have been eliminated thus removing a source of dust that can cause motor failure. 

The screw-crammer system uses a conical hopper with a screw that is driven by a separate gear reducer and variable-speed drive motor. The output and effectiveness of the crammer are determined by the screw configuration and the available speed. The ram-type system, on the other hand, uses a pneumatic ram to stuff material into the screw. The ram is a piston-driven unit with the stroke timing adjustable by setting a series of timers located in the control panel. The feed section used by the ram system has an opening that is 12-14 times larger than that of a standard screw extruder. This allows low-bulk-density material to flow freely into the feed throat where the ram can compress it into the screw. Depending on the extruder size, the ram can compact materials with a force of 2000-9000 psi. 

Rotary valves require a timer/power source that provides an adjustable DC output (6 to 24 V) for motor drive and a digital time-set for motor on-time, forward and reverse (1 ms to 99.99 s). 

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