I have been tasked with measuring both the voltage and current output of a plasma system but have only been provided and oscilloscope to do this (Tektonix TBS 2000 Series 100MHz, 1G/s) and a high voltage probe (Tektronix P5100A, 500MHz, 40Mohm, 2.5pF, 100X:1000V CAT II). The system consists of a variable transformer connected to the main which then has a "Neon Power Supply" connected (Input: 120VAC 50/60Hz 0.9A, Output: 10kv 30mA) leading to the plasma "chamber". I have tried to connect the oscope probe to just the power supply to see the voltage output but receive what can only be described as high pulses of voltage which increase in frequency as I increase the voltage on the transformer. When connected to the plasma "chamber" these pulses in voltage can be seen to cause the plasma to pulse as well.

In order to measure the voltage and current of the system with the use of the oscilloscope how could it be done? I was able to source a handheld DMM (Tektronix DMM157) and have had the idea of building a voltage divider in order to then measure the voltage (using 47, 510kohm resistors as R1 and 3, 430kohm resistors as R2) but I am not entirely to sure how safe this would be especially with such high voltage. Any help is greatly appreciated!

  • 1
    \$\begingroup\$ What's the duty cycle of the voltage pulses? I'm guessing your DMM will be too slow to be of much use here \$\endgroup\$ – Chris Fernandez Jul 8 at 20:10
  • \$\begingroup\$ You've stated that your oscilloscope probe runs to 1000V, but the Neon Power Supply output is listed as 10kV. Are you actually running at 10kV or something significantly lower than that to start? Don't hurt your oscilloscope or probe! \$\endgroup\$ – Chris Fernandez Jul 8 at 20:12
  • \$\begingroup\$ @ChrisFernandez From what I can see I don't believe I am running the 10kV, the transformer essentially acts as a potentiometer, allowing me to control the input voltage leading into the power supply. I never reach that 120VAC that is required by the power supply to output 10kV. The high voltage pulses however can be seen to occur from 20-50VAC when set on the transformer. \$\endgroup\$ – wute Jul 8 at 20:52
  • 1
    \$\begingroup\$ Tektronix makes 1000X probes, that is the right way to measure HV pulses. Any divider made with high value resistors will not be accurate at high frequencies. Scope probes that attenuate have a tiny cap in parallel with the series resistor to keep the voltage divider ratio (with the scope impedance) relatively constant at higher frequencies. \$\endgroup\$ – Mattman944 Jul 8 at 21:21
  • \$\begingroup\$ You will need at least 3GHz if you want accurately capture the rise time of current using 50 Ohm semi-rigid coax terminated with 50R. Why not 100MHz?. It will be faster and unsuitable for any probe you have. attenuators to 50R are ok Too. Voltage measurements also will be done with RC dividers to 50 Ohms with balanced reactance. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 9 at 4:15

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.