# Scope Probe method For Voltage Of High Voltage Pulse?

#### russwr

Joined Aug 29, 2017
35
Is it proper to use a 1 ohm resistor on GROUND side of return negative line back to DC power supply , and then measure the low volts with scope probe over the resistor. The Amp flow will be the same as the volts. I = E / R . 6A = 6v read over 1ohm resistor is 6 amps pulse current. The high voltage diode DC at same time firing to ground would not interfere.

#### KeithWalker

Joined Jul 10, 2017
3,029
I don't quite understand the details of what you are proposing to do. Can you draw a diagram?

#### Dodgydave

Joined Jun 22, 2012
11,239
Are you trying to use the scope as a current meter, by looking at a pulse across a resistor?

#### k1ng 1337

Joined Sep 11, 2020
910
Is it proper to use a 1 ohm resistor on GROUND side of return negative line back to DC power supply , and then measure the low volts with scope probe over the resistor. The Amp flow will be the same as the volts. I = E / R . 6A = 6v read over 1ohm resistor is 6amps pulse current. The high voltage diode DC at same time firing to ground would not interfere.
Your last sentence is vague. You can monitor current through a shunt resistor by looking at the voltage across it according to Ohm's law. Scope probes are common with 1:1 or 1:10 scaling. Ideally you want the shunt to a very low value otherwise it loads the circuit. Look up a video how to make a 0.1ohm or less shunt with a multimeter, I use power resistors myself. It may be advantageous to monitor high side currents as well to determine the common mode distribution. Use KVL and KCL to calculate and confirm your findings.

#### MisterBill2

Joined Jan 23, 2018
17,794
A small resistance in a high voltage supply return connection is rather common in amateur radio power amplifiers, and it works quite well. BUT there can be problems and so the technique must be used carefully, because there are several potential hazards and problems.
First, there exists a common tendency to connect the negative power supply circuit to the physical support of both the load portion of the system, and the power supply portion of the system. This would tend to compromise the measurement accuracy. The potential hazard exists if somehow the resistor becomes open circuited, in which case there may tend to be a voltage between the two assemblies.
Fortunately the solution that avoids problems is to arrange the source power supply so that the negative side is isolated from the support portion of its construction, except for that shunt resistor, and to assure that the power rating of that resistor is adequate to provide a reliable connection even in the event of an overload. , and to assure that the grounded end of the shunt resistor is adequately connected to the framework of that portion of the system. (The chassis).
The one other caution is to assure that all portions of the high voltage portion of the system are not connected to the mains supply circuit.