A direct display plasma density and temperature meter was developed using a floating double probe and a Langmuir probe. A small AC voltage was superposed on the DC voltage and in the floating double probe method the third harmonic component of AC current was detected. The phase reversal of the 3rd harmonic component was observed at V
dc=V
* + 1.30 kT
e, and an experiment was carried out to fix the DC voltage automatically at this voltage V
* detecting the phase reversal of the 3rd harmonic component. The plasma density and electron temperature were obtained directly from the DC volage V
* and the DC current corresponding to the voltage V
*. Similarly, the second harmonic component of AC current was utilized in the Langmuir probe method and the DC voltage was automatically fixed at the inflection point of Langmuir probe characteristic. The plasma density and temperature can be obtained from the DC and AC currents at the inflection point.
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