4.2Electronic Control
4.2.1 Microprocessor Control
The pump is controlled by hybrid microprocessor circuitry which
(1)provides control signals to the motor drive circuitry, (2) interfaces with the keyboard/display, (3) receives signals from the refill flag, and
(4)provides external input/output
An eccentric cam provides refill in a fraction of the full cam cycle. The remaining revolution of the cam provides piston displacement for outward flow of the mobile phase. In addition to the rapid refill characteristics of the drive, the onset of refill is detected by an infrared optical sensor. The microprocessor changes the refill speed of the motor to an optimum for the set flow rate. At 1ml/min, the refill rate is more than five times faster than if the motor operated at constant speed. The optimum refill rate minimizes the resulting pulsation while avoiding cavitation in the pump head.
The flow rate of any high pressure pump can vary depending on the operating pressure and the compressibility of the fluid being pumped. The Binary Solvent Delivery Module is calibrated at 1000 psi using an 80:20 mixture of water and isopropanol.
4.2.2 DC Power Supply
Power for the pump is provided by a switching power supply which accepts voltages from 90 – 240 VAC. Output is 24 VDC for the pumps and heater. A switching 5 VDC supply is also provided to power control and display circuits.
4.2.3 Remote Interfacing
Appendix A for information on operation via this connection.
4.2.4 Motor Stall Detector
The motor can stall and create a loud buzzing sound if the flow path connected to the pump's outlet becomes plugged, if the pressure exceeds the maximum pressure rating of the pump, or if the mechanism jams. If a motor stall occurs, the electrical current being supplied to the motor is turned off and the fault light is turned on.
The Motor Stall Detector is enabled or disabled during
