# Voltage Divider Multiplier Value Too High?

After constructing a voltage divider to reduce the voltage from my power supply (Output 10kV, 30mA) an oscilloscope probe was used in hopes of measuring the output voltage of the system. Due to the way this system functions a DMM could not be used due to the high pulses of voltage outputted by the power supply as the input voltage increases. That is why I thought it would be best to use an oscilloscope with a voltage divider to measure this voltage. In my case the voltage divider was configured where R1 = 64.1MΩ and R2 = 1.298MΩ (R1 was initially set at 23.00MΩ however my oscilloscope could not read the output voltage as high as was needed so the resistance of R1 was increased). After performing the calculations necessary to determine the amount the output voltage seen on the oscilloscope needs to be multiplied by, a multiplier of 52.15 is produced. I followed the math seen on this post (Measure high voltages with a multimeter) which resulted in this value however it seems to be too high. Did I simply calculate incorrectly or is the equation found there incorrect? (A high voltage probe is being used with an impedance of 40MΩ which has been taken into account when calculating the multiplier.)

• Remember that a typical oscilloscope has an input impedance of 10 MΩ with a 10x probe. – Hearth Jul 23 at 19:24
• You said pulses. What's the bandwidth of these pulses? What's the bandwidth of your scope and probes? – DKNguyen Jul 23 at 19:32
• I am using a Tektronix P1500A probe which has a bandwidth of 500MHz and impedance of 40MΩ on a Tektronix TBS2000 Oscope with a bandwidth of 100MHz at 1GS/s. The bandwidth of the pulses themselves are unknown as oscope cannot seem to measure them while connected to the divider. – custokumla Jul 23 at 19:43
• In which order did you put the resistors? – Voltage Spike Jul 23 at 19:45
• @VoltageSpike The larger 64.1MΩ resistor is the first in the series and the 1.298MΩ resistor is the one being measured off of by the oscilloscope. – custokumla Jul 23 at 19:46

Your probe has an input impedance of 40M$$\\Omega\$$ in parallel with 2.5pF, according to this Tektronix page. At, say, 100kHz the 2.5pF has a reactance of < 1M$$\\Omega\$$, so it acts as a low-pass filter.