STAND-ALONE MICROPROCESSOR-CONTROLLED FAST SWEEP LANGMUIR PROBE DRIVER

This article describes a power supply and data logger for a Langmuir p robe 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 possib le. Probe current measurements are in the range from -1.0 to +100 mA w ith a precision of 5 mu A on the most sensitive range, while the volta ge 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 pro cess of analog-to-digital conversion and to provide effective noise su ppression; a solution to the problem of floating the power supply on t op of the potential developed across the grounded current sensing resi stor based on the power supply rejection ratio characteristics of a hi gh voltage operational amplifier; and the development of an interface and control board employing the GPIB protocol to communicate with a ho st 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.