Rigol 2072a Oscilloscope - 230V Mains - Switching Power Supply Probing - Page 1
Forum section: electronics / testgear

author: donkey
author_rank: Regular Contributor
timestamp: October 14, 2018, 01:16:07 pm
content: I bought a Rigol 2072a Oscilloscope for switching power supply repairing purposes. There is a"All inputs 1Mohm//16pF CAT I 300V rms, 50 Ohm <= 5V rms"raiting is written in front of the Oscilloscope.I bought anOscilloscope probe G3100(1: 100, 250 MHz, 2.5 kV) which is rated as followsBandwidth: 100 MHzRise time: 27.5 nsDivision ratio: X100 ± 2%Performance technology: SMDInput voltage: <2500VIncoming resistance: 100 MΩInput Capacity: 3.5 - 10.5 pFIn the switching power supply there are points where i read 400V dc voltages with digital multimeter and i am really worried about to damage my Oscilloscope by doing something stupid.I want to visualize:The rectified signalThe switching signal of the gateThe switching response of the transistorThe oscillation of the transformer at the primary and the secondary side.Condition:By connecting this 100X 2.5 kV raiting probe to the Rigol 2072a Oscilloscope and floating the device under test.Question:May i probe any two points of the switching power supply without damaging the probe and the Oscilloscope?Thank you very much!

author: Performa01
author_rank: Super Contributor
timestamp: October 14, 2018, 01:28:07 pm
content: You will not damage your probe or scope if the DUT is floating.But you need to be aware that whatever you're probing, the shields and chassis of the DUT well be at a high voltage as soon as you connect the scope ground anywhere behind the mains rectifier. So don't touch it!

author: JFJ
author_rank: Regular Contributor
timestamp: October 14, 2018, 08:48:32 pm
content: Quote from: donkey on October 14, 2018, 01:16:07 pmBy 'floating' you do mean powering the device under test via an isolation transformer?

author: nctnico
author_rank: Super Contributor
timestamp: October 14, 2018, 09:26:41 pm
content: Quote from: JFJ on October 14, 2018, 08:48:32 pmOh, please don't float the DUT or your oscilloscope if you value your life. There is much more to it then just connecting an isolation transformer somewhere in the middle.The only safe way to do these kinds of measurements is to use a CAT rated differential probe. These cost money but not so much compared to an isolation transformer. With multiple differential probes you can probe any point.

author: donkey
author_rank: Regular Contributor
timestamp: October 15, 2018, 02:17:24 am
content: Quote from: JFJ on October 14, 2018, 08:48:32 pmYes JFJ, I mean powering the device under test via an isolation transformer.

author: donkey
author_rank: Regular Contributor
timestamp: October 15, 2018, 02:27:09 am
content: Quote from: nctnico on October 14, 2018, 09:26:41 pmThank you for your concern nctnico!I am not going to touch anywhere else on the DUT because of it is connected to an isolation transformer. I am not using the isolation transformer to secure my life but to secure the oscilloscope. Is it that dangerous to use an isolation transformer? Do this setup may ruin my oscilloscope? If so, which differential probe you may recommend? What must be the test setup? I have a 2 channel oscilloscope.Thank you!

author: Performa01
author_rank: Super Contributor
timestamp: October 15, 2018, 08:49:17 am
content: Of course a differential probe is the correct way to do it - the isolation transformer is just a workaround for people who are aware of the risks for their health - though widely used, at least in the past.I would recommend a Testec TT-SI-9001 (25MHz, €265,-) or TT-SI-9101 (100MHz, €510,-). Net prices from Batronix, Germany.

author: Ice-Tea
author_rank: Super Contributor
timestamp: October 15, 2018, 08:53:27 am
content: Quote from: donkey on October 15, 2018, 02:27:09 amYes. As mentioned before: every metal part on your scope that you can touch (BNC connectors, parts of the chasis,...) will be connected to mains.

author: donkey
author_rank: Regular Contributor
timestamp: October 15, 2018, 09:30:01 am
content: Quote from: Performa01 on October 15, 2018, 08:49:17 amThank you Performa01 for your recomendation. I made a research on some differential probes i can find local stores and the lowest price i get was the one you recomended.It is 6 times the price of the isolation transformerand almost the same price of the oscilloscope. I haven't bought the isolation transformer yet and now i have to re-consider my test setup.Thank you for your help.

author: donkey
author_rank: Regular Contributor
timestamp: October 15, 2018, 10:35:43 am
content: Quote from: Performa01 on October 15, 2018, 08:49:17 amI have found a Testec TT-SI-9002 model which is rated for 20x and 200X 1400V. Which one is better to buy? If i buy this differential probe may i use the probe without any isolation transformer and measure any two points of the switching power supply without damaging the probe and the oscilloscope?Thank you!

author: Performa01
author_rank: Super Contributor
timestamp: October 15, 2018, 11:12:12 am
content: Quote from: donkey on October 15, 2018, 10:35:43 amI would think x10 and x100 is more convenient than x20 and x200, but it really shouldn't matter much. The voltage rating is the same for both probes and the x100 probe factor should be fine for just about anything up to 1400V.With the differential probe you can measure any voltage difference in the circuit, as long as both individual voltages do not exceed +/-1400V with respect to your oscilloscope ground (which has to be earth potential!).EDIT: And yes, of course you should NOT use an isolation transformer when you work with the differential probe. Both the scope and the DUT should be grounded!

author: capt bullshot
author_rank: Super Contributor
timestamp: October 15, 2018, 01:29:22 pm
content: Quote from: donkey on October 15, 2018, 02:17:24 amYes, that'll work. The probe ground clip will ground the DUT at the point it is connected. So do not connect the ground clip to a switching node (e.g. the source of a high-side MOSFET in a half bridge circuit to view its gate). This may lead to anything from just works to DUT destroyed. Other DC (or line frequency AC) potentials such a the "-" of the bulk capacitor will be OK. As others said, be aware of your personal safety when doing so.

author: nctnico
author_rank: Super Contributor
timestamp: October 15, 2018, 01:32:12 pm
content: Quote from: donkey on October 15, 2018, 10:35:43 amAnother brand to consider when looking for differential probes is MicSig. The DP10013 for example. These offer excellent value for money.

author: cnkz
author_rank: Contributor
timestamp: October 15, 2018, 02:58:51 pm
content: You can also use two isolation transformers. One for the scope and one for the DUT.But nevertheless be aware that touching two points of the DUT is still dangerous! (Or the scope and one point of the DUT)

author: tryode
author_rank: Newbie
timestamp: October 15, 2018, 03:57:33 pm
content: Quote from: capt bullshot on October 15, 2018, 01:29:22 pmWith a 2 (or 4 or whatever how many) channels scope with x100 probes you can use them in a "differential way" too with some math. Of course having the ground clip connected to ground and their tips to the measuring points e.g. for a HB high side driving voltage.Anyway be very careful with mains driven stuff because you can kill yourself.

author: maginnovision
author_rank: Super Contributor
timestamp: October 15, 2018, 04:49:38 pm
content: Quote from: blueskull on October 15, 2018, 03:01:44 pmYea, I'm curious whether they made every number up or what happened.

author: donkey
author_rank: Regular Contributor
timestamp: October 15, 2018, 06:20:33 pm
content: Quote from: maginnovision on October 15, 2018, 04:49:38 pmI bought the probe from this supplier. The specifications are written as such.https://supereyes.ru/catalog/Aksessuary_k_multimetram_ostsillografam_generatoram/SCHup_k_ostsillografu_s_delitelem_G3100_1_100_250MGts_2_5_kV/

author: donkey
author_rank: Regular Contributor
timestamp: October 15, 2018, 06:21:44 pm
content: Thank you all of you for your help

author: nctnico
author_rank: Super Contributor
timestamp: October 15, 2018, 06:32:02 pm
content: Quote from: maginnovision on October 15, 2018, 04:49:38 pmIt is not uncommon for sales people to have very little knowledge of what they are selling. Last week I bought a piece of heavy duty chain to pull a tree from my garden. The sales guy didn't seem to know how to operate a caliper to measure the thickness of the shackles to make sure he sold me the right sized chain.

author: donkey
author_rank: Regular Contributor
timestamp: October 15, 2018, 07:15:16 pm
content: Quote from: nctnico on October 15, 2018, 01:32:12 pmEdited: I decide to go with the MicSig DP10013 differential probe. MicSig has half the price of the Testec TT-SI-9001 for sure but what i concern is if it has the half specifications of the Testec TT-SI-9001 model?What an x500 vs x100 probe effects in measurement?Which one you would choose?Thank you!

author: nctnico
author_rank: Super Contributor
timestamp: October 15, 2018, 07:24:08 pm
content: I think the quality of the design is equal. The one from Testec looks like a Pintek rebrand. 99% of the differential probes you find on the market are Pintek rebrands or clones. The one from MicSig is a rare exception to that hence the better price point.

author: donkey
author_rank: Regular Contributor
timestamp: October 15, 2018, 07:27:41 pm
content: What an x500 vs x100 probe effects in measurement?

author: Performa01
author_rank: Super Contributor
timestamp: October 15, 2018, 07:36:38 pm
content: Quote from: donkey on October 15, 2018, 07:15:16 pmin short: five times less input sensitivity.Your DSO is expected to have high sensitivity with low noise, yet I would try to stay at or above 5mV/div for reasonably noise-free measurements.With a x100 probe, this translates to an actual sensitivity (at the probe tips) of 500mV/div (4Vpp full scale). This should be fine for just about anything within a SMPS with MOSFETs, except maybe the voltage across a current sensing resistor.With a x500 probe, this translates to an actual sensitivity (at the probe tips) of 2.5V/div (20Vpp full scale). This sounds uncomfortably insensitive to me...

author: donkey
author_rank: Regular Contributor
timestamp: October 15, 2018, 08:06:30 pm
content: Quote from: Performa01 on October 15, 2018, 07:36:38 pmWhere i live the mains voltage is over 230V's and at the fully rectified portion of the signal reaches about 400V's DC.In the MicSig DP10013 differential probe specifications states thatMaximum Differential Test Voltage（DC+AC PK-PK）: 130V（50X）1300V（500X）Maximum input common mode voltage（DC+AC PK-PK）: 130V（50X）1300V（500X）Does this specification means that i only can use 500x atenuation rate for my device under test or may i use the 50X atenuation without problem?Thank you!

author: Performa01
author_rank: Super Contributor
timestamp: October 15, 2018, 09:23:05 pm
content: Quote from: donkey on October 15, 2018, 08:06:30 pmYes I have the same mains voltage and a maximum voltage of about 400Vp should indeed be expected.And yes, that means you can only use the higher attenuator setting.This is exactly why I've recommended the TT-SI 9001. In the 100:1 setting, it can handle +/-700V which is plenty for what you need. On the other hand, you have still the 10:1 setting whenever you need differential measurements in some ordinary circuit, where you can safely probe up to +/-70V and have the same attenuation as with any regular 10:1 probe.

author: pantelei4
author_rank: Regular Contributor
timestamp: October 17, 2018, 06:16:45 am
content: I use Rigol 2072a + Micsig DP10013 for measurements in hot connections.Oscillograms of 1 MHz meander, amplitude 5 V, band limitation 100 MHz- DP10013 delay around 5ns (blue 10X, yellow 50X)- noise 50X- noise 500X

author: David Hess
author_rank: Super Contributor
timestamp: October 19, 2018, 01:12:06 pm
content: 300 volts RMS is 425 volts peak so there should be no problem. Rigol's lack of frequency derating makes this specification fuzzy so I would not trust it; it could be better or worse so take your chances.Note that a typical x100 probe will *not* protect the oscilloscope from excessive DC voltage when AC coupling is used. These probes need to be used with DC coupling at high voltages.

author: VooDust
author_rank: Regular Contributor
timestamp: February 15, 2022, 06:37:46 am
content: Quote from: David Hess on October 19, 2018, 01:12:06 pmHow so?

author: Performa01
author_rank: Super Contributor
timestamp: February 15, 2022, 12:39:41 pm
content: Quote from: VooDust on February 15, 2022, 06:37:46 amThe typical x100 probe is (simplified) just a 99 meg series resistor with a cpacitor across.So, if the scope input is open circuit for DC in AC-coupled mode, the full voltage present at the probe tip will charge the internal DC-blocking capacitor of the scope up to the full voltage within seconds. Since the capacitor is unlikely to be rated for much more than 400V, it might not survive an input voltage of e.g. 1000V, but if it does (not unlikely) it will hold some substantial amount of energy when fully charged. If you connect some low impedance source to the scope input after this, the input capacitance will discharge into the input buffer of the scope, where some parts might not be too hapy seeing voltages much higher than 400V.Thankfully, this is only a problem with certain (mostly obsolete) designs.The vast majority of mdern general purpose oscilloscopes with high impedance inputs have a different input architecture and AC-coupling is solved differently.As a consequence, most modern GP DSOs provide a constant input impedance, regardless of the input coupling.One can easily check this with a DMM: can you still measure the 1 meg ohms input impedance in AC coupled input mode? If so, you are safe to use the x100 HV-probe without further considerations.