Stand-alone microprocessor controlled fast sweep Langmuir probe driver

This article describes a power supply and data logger for a Langmuir probe interfaced to a personal computer. The system provides a voltage sweep range from -125 to +100 V in 100 steps in a time similar to 0.15 s. Restricted sweep ranges and single point operation are also possible. Probe current measurements are in the range from -1.0 to +100 mA with a precision of 5 mu A on the most sensitive range, while the voltage may be set with a precision of 56 mV. Novel features of the system include: the use of integrate-and-dump techniques to implement the process of analog-to-digital conversion and to provide effective noise suppression; a solution to the problem of floating the power supply on top of the potential developed across the grounded current sensing resistor based on the power supply rejection ratio characteristics of a high voltage operational amplifier; and the development of an interface and control board employing the GPIB protocol to communicate with a host computer. Successful operation of the system has been demonstrated in the electrically noisy environment of a helicon plasma source. (C) 1997 American Institute of Physics.