Picoscope 2000 series, 10x probes and transformer - Page 1
Forum section: electronics / beginners

author: T_Tesla
author_rank: Newbie
timestamp: February 08, 2018, 02:29:29 am
content: Hi there!Working with a lab assignment for the moment, and with my PC and picoscope, I´m suppose to connect the probe to the scope (BNC), and in the other end of the probe ------> transformer.And since I have a passive 10x probe, I should use the ground clip, right?But when connecting the probe to the transformer, I have no idea of where I should connect the ground clip.Any answers are well appreciated! x)

author: Cliff Matthews
author_rank: Unknown
timestamp: February 08, 2018, 03:14:32 am
content: Have a look at this video and afterward, give a little more detail on what you need to achieve. Remember USB ground is still a ground.

author: T_Tesla
author_rank: Newbie
timestamp: February 08, 2018, 04:02:01 am
content: ok, will look at the clip. But I have the following circuit so to speak. (very simplified)PC---->scope--->probe---->Transformer------>MAIN OUTPUT<--------electronic item.I am suppose to connect the electronic item and the transformer at the same time, and look for some kind of drop voltage in the scope software.I´m almost 100 % sure that when you have a passive probe, you are suppose to connect the ground clip and measure the voltage between the probe tip and the ground clip.But as I was saying. Have no idea of where to connect the ground clip.PS. Am aware of the USB ground, but my teacher described the ground clip-connection as something crucial.

author: Cliff Matthews
author_rank: Unknown
timestamp: February 08, 2018, 12:06:44 pm
content: When you say main output, do you mean "mains output"? At times, many on the forum here are very hesitant to give advice on scopes connecting to places that could hurt someone.. Is there any more detail you can give? Eg. Transformer voltages, size, what side (primary or secondary) or type? What is the device.. Etc..

author: T_Tesla
author_rank: Newbie
timestamp: February 08, 2018, 04:04:08 pm
content: Absolutely! Mains putput is the correct word.The transformer is a 230/12 V and the secondary side connects to the probe.The idea is to for example connect a vacuum cleaner (preferably an old model), at the same time you connect the primary side of the transformer in the mains output.You are suppose to have a current spike as soon as you start the vacuum cleaner, and therefore a drop voltage.Hope you know what I mean by that.Don´t know what else I can describe, anything else you need to know?

author: Vtile
author_rank: Super Contributor
timestamp: February 08, 2018, 04:53:39 pm
content: So you have step-down transformer 230/12 Vac, where you attach your scope to at the 12Vac side. Is this correct.The intention is to observe the transient effect of the mains (230Vac) network and the vacuum cleaner acts as a transient "generator" at the mains network is this correct.Is your transformer grounded, do you know how to measure if it is grounded or not. Same question with another way around, is your 230/12Vac transformers output (12Vac) galvanically isolated.Is this correct?

author: T_Tesla
author_rank: Newbie
timestamp: February 08, 2018, 05:09:45 pm
content: Vtile .. you are correct!The output of the transformer is not galvanically isolated.But I´m curious about what decides if you should use the ground clip or not?As many have pointed out earlier, I have a USB-ground, but apparently that isn´t enough.I have to use the ground clip, and I wonder exactly why and where?

author: Vtile
author_rank: Super Contributor
timestamp: February 08, 2018, 05:27:13 pm
content: Quote from: T_Tesla on February 08, 2018, 05:09:45 pmHmm.... OK.Well the ground clip usage depends on the circuit you are measuring. In this case when the output of the transformer is not galvanically isolated you need to measure which pin of the output is ground connected, then you attach your ground clip to that grounded pin and the actual probe to another pin.I'll not give you whole answer as this is meant to be a lab work, where you study the subject (..and learn).PS. The use of ground clip is a two fold thing. On the other hand it can damage your equipment or even you as the user (ie. when measuring 230Vac), but on the other hand it is needed for better measurement. The ground clip is actually a reference point for the measurement, but since it is almost always also connected to the safety ground of the laboratory mains (ie. through USB connection) it makes a few things (or tricks) possible and a few things impossible.

author: T_Tesla
author_rank: Newbie
timestamp: February 08, 2018, 05:37:57 pm
content: Ok, that means I was on the right track two days ago x) ...But I feel it isn´t enough to be like 80 % sure in this area, so I didn´t dare to continue with connecting the load.But I will continue with measuring the pins of the output in order to decide which one of them is grounded, as you were saying.Thanks for the answers!

author: T_Tesla
author_rank: Newbie
timestamp: February 08, 2018, 07:00:55 pm
content: Forgot to mention one significant thing, sorry about that.The transformer is a plugin, with two open ends on the secondary side ... would have been a lot easier with an 8-pin transformer or something like that.So I´m not quite sure about the measurment to determine the ground point.This is the downside of 90 % work with theory and 10 % work with the practical things.A lot of question marks shows up along the way in my practical assignments. -_-PS. My teacher is the slowest guy in the world when it comes to answering questions, that´s why I botter you with this. x)

author: Vtile
author_rank: Super Contributor
timestamp: February 08, 2018, 08:30:25 pm
content: I do start to question the transformer setup. Do you have a picture of it? If no, can you describe it further, which kind is the primary connections? Is the primary connection fixed or through power cord, which you can freely attach. Is the transformer in the box or open setup on the laboratory environment, do you see both the primary and secondary connections?Which level of education system you are currently studying, I do ask so I can judge how much background information you might have and how detailed information you really need.Draw or take a picture, it would clarify the situation. In general this is really super simple if the secondary of the transformer is floating / galvanically isolated. Easy if the transformer is not galvanically isolated, but the mains connection is fixed to the wall / laboratory table. A bit more interesting if the transformer is connected with typical three pin schuko connector and the secondary is grounded.