Measure higher voltage using oscilloscope - Page 1
Forum section: electronics / beginners

author: Daan32
author_rank: Newbie
timestamp: September 21, 2020, 07:39:11 pm
content: Ok so this isn't really clear to me,My picoscope 2203 can only measure up to 20Vdc, but I want to be able to measure 70Vdc,Will it work when I set my probe to x10 and my scope to x1, or the other way around?Or will I end up blowing it up anyway?Thanks in advance!

author: bdunham7
author_rank: Super Contributor
timestamp: September 21, 2020, 07:54:05 pm
content: If you use a normal 10X probe, the voltage at the scope input should be 1/10 of actual--so 7V in your case. If the Picoscope software allows you to set probe attentuation, you can set it to 10X and the displayed voltage will be correct--it will multiply the actual voltage that it sees by 10X. The probe attentuation setting doesn't actually change anything on the input of the scope, it just changes how the display is labelled. Your scope is 'protected' to +/- 100V, so even if you make a mistake you shouldn't blow anything up. Make sure you understand all of these things before you try this on any voltage more than 100 volts.

author: Ian.M
author_rank: Super Contributor
timestamp: September 21, 2020, 08:01:42 pm
content: As long as the probe is rated for the voltage it will work, and just about any common x10 probe should be rated for several times more voltage. Your Picoscope's inputs are protected up to +/-100V DC, so even if you make a mistake, provided you don't put the ground clip on a voltage rail*, it should be OK.Caution: if you use a switchable x1/x10 probe to probe a voltage exceeding the absolute maximum input voltage rating of your scope, you are only one slip of your finger from blowing up your scope. Also, scope probes typically have a voltage rating (DC + peak AC) that's only good up to a particular frequency. Above that frequency their rating typically decreases with respect to frequency. Know your probe's specification, don't probe outside its limits, and if you regularly need to probe higher voltages, invest in an appropriately rated non-switchable x10 or even x100 probe.* Your scope has the BNC shells connected to ground via your PC. If you connect the probe ground clip to a point (node) in your circuit that is not ground, and any other connection introduces a ground reference to a different node, the resulting potential difference may cause large currents to flow through your probe lead's screen, ground tracks on your scope PCB, the USB lead and your PC's motherboard. If you are really lucky you'll just melt your probe lead, but there is a high risk of blowing your scope and even your PC motherboard.Be <expletive> careful *where* you put the ground clip, and if in doubt check for ground offset between the clip lead and the target node with a CAT-II or better DMM on a low impedance voltage range (or with a 5W 22K resistor in parallel with the meter if it doesn't have low-Z voltage ranges) *before* connecting the ground clip.

author: Zero999
author_rank: Super Contributor
timestamp: September 21, 2020, 08:55:19 pm
content: If you want to measure 70VDC, then you need a voltage meter, commonly known as a multimeter these days. An oscilloscope is the wrong tool for the job.

author: rstofer
author_rank: Super Contributor
timestamp: September 22, 2020, 07:36:39 pm
content: I have a problem with 1X/10X switchable probes when I know for a fact that I require 10X forever and ever. Just a slight 'oopsie' with the switch and things get expensive.To preclude this on my Analog Discovery 2, I bought a pair of ProbeMaster 10X FIXED probes. I never need to think about the switch position. Model 3904-2https://probemaster.com/3900-series-scope-probes-100-mhz/A pair of probes is a lot cheaper than replacing the AD2.

author: Refrigerator
author_rank: Super Contributor
timestamp: September 22, 2020, 08:49:07 pm
content: Quote from: rstofer on September 22, 2020, 07:36:39 pmTape, glue or whatever that will hold the switch in place would suffice. I've personally never had the X10 switch flick accidentally (knock on wood).

author: WattsThat
author_rank: Frequent Contributor
timestamp: September 22, 2020, 10:27:23 pm
content: Quote from: Refrigerator on September 22, 2020, 08:49:07 pmFor some reason, it always takes me way too long to figure out my probe is on x1 instead of x10.I’m thinking a piece of low temp heat shrink might be a long term solution to the problem. Thank you for the idea!

author: jnz
author_rank: Frequent Contributor
timestamp: September 23, 2020, 04:22:08 am
content: Dumb question but... if your probe in switchable probe in 1X handles upto 300V and your scope handles 400V, and the absolute highest voltage you ever expect to see is 120V, what’s are some reasons to use 10X?

author: bdunham7
author_rank: Super Contributor
timestamp: September 23, 2020, 04:32:08 am
content: Quote from: jnz on September 23, 2020, 04:22:08 amA typical scope might have a maximum setting of 5V/div or 10V/div, so 8 divisions would be 40 or 80 volts peak-to-peak or about 14 or 28 volts RMS. The 400V marking you see on the scope is the maximum allowable input that probably won't blow it up, not the maximum it can display.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: September 23, 2020, 05:09:59 am
content: Quote10x has a lower capacitance.

author: Zero999
author_rank: Super Contributor
timestamp: September 23, 2020, 07:36:21 am
content: Quote from: JustMeHere on September 23, 2020, 05:09:59 amAnd higher input resistance. A lower capacitance and higher resistance, mean it loads the circuit being tested, less. The x1 setting is also has an upper cut-off of around 7MHz. It's only good for audio and low impedance circuits.There are a couple of disadvantages of x10 probes: higher noise and it increase the oscilloscope's minimum volt/division setting by a factor of 10.