Measuring 200V signal with cheap digital oscilloscope - Page 1
Forum section: electronics / beginners

author: NivagSwerdna
author_rank: Super Contributor
timestamp: October 17, 2017, 10:17:50 am
content: I have a Rigol 1052E scope (it's my pride and joy) which has scope probes marked x1 and x10.I think it is probably safe to put a probe on x10 and connect it to my 180V Nixie power supply to look for signs of sag under transient load.Does that sound safe?My interpretation of the specification is...Input Impedance 1M?±2%, the input capacity is 18pF±3pFProbe Attenuation Factors 1X, 10XMaximum Input Voltage 40V (DC+AC Peak)Thanks in advance.

author: Gyro
author_rank: Super Contributor
timestamp: October 17, 2017, 10:44:46 am
content: Yes, that sounds safe to me on x10.A higher current supply, I might think twice about and go for a x100, just from the safety perspective, but a Nixie supply shouldn't be an issue.

author: tggzzz
author_rank: Super Contributor
timestamp: October 17, 2017, 10:51:30 am
content: Check the probe's voltage rating, noting its frequency dependence.If you have a *1/*10 switchable probe, it won't be long before you use it with the wrong position.Why not use a voltmeter, or add two resistors as a potential divider and measure the divided voltage?

author: Ian.M
author_rank: Super Contributor
timestamp: October 17, 2017, 10:52:13 am
content: Safe for you, certainly. Safe for the scope with a switchable x1/x10 probe of unknown ratings is not so certain.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: October 17, 2017, 11:01:46 am
content: The probes came with the scope... I think they are...PVP2150: 1X/35MHz, 10X/150MHz, one/two Probes Kit10X or 1X Switchable10 pF to 25 pF Compensation Range1X: 1M? ±1% input resistance 50 pF ±20 pF input capacitance 150 VRMS CAT II max. rated input voltage10X: 10M? ±1% input resistance 10pF ±5pF input capacitance 300 VRMS CAT II max. rated input voltage

author: NivagSwerdna
author_rank: Super Contributor
timestamp: October 17, 2017, 11:05:58 am
content: Quote from: tggzzz on October 17, 2017, 10:51:30 ama potential divider is a possibility but I assume the input impedance of the scope is significant. Thought I would go simple if I could.

author: fcb
author_rank: Super Contributor
timestamp: October 17, 2017, 11:07:58 am
content: My DS1054Z says "1Mohm//13pF 300VRMS CAT1" by the BNC inputs, which equates to +/-424V peaks!However, I wouldn't use the scope on these voltages without good quality 10:1 probes.

author: tggzzz
author_rank: Super Contributor
timestamp: October 17, 2017, 12:32:18 pm
content: Quote from: NivagSwerdna on October 17, 2017, 11:05:58 amSimpler is always better,iffpossible.Impedance effects are predictable and can be allowed for.The input impedance of the *10 probe is 10MHz//15pF. The output impedance of the potential divider = r2/(r1+r2) i.e. ~r2 for a 100:1 divider, and the current it takes from your circuit is defined by r1+r2. What frequencies are you expecting to observe, since that will define the effect of the 15pF?Don't, whatever you do, have r2=infinity and rely on the scope's input impedance; any slip could put the entire voltage across the scope.

author: rstofer
author_rank: Super Contributor
timestamp: October 17, 2017, 06:06:20 pm
content: Quote from: fcb on October 17, 2017, 11:07:58 amAnd that rating is the same as in the Specifications section of the User Manual EXCEPT the scope is only rated 100 Vrms CAT II. I suspect we are really talking about CAT I so 300 Vrms it is.And that is with x1 probes because the spec is for the voltage seen at the BNC. The x10 divides the voltage before it gets to the BNC.I would certainly use x10 but I use x10 for everything. So the scope is seeing something like 20V and 5V/div is more than adequate. If I did mess up and have the probe on x1, I wouldn't expect anything to happen to the scope because the voltage is well within the specs.