DOS questions

Discussion in 'General Electronics Chat' started by Shagas, Jun 22, 2014.

  1. Shagas

    Thread Starter Active Member

    May 13, 2013
    802
    74
    Hello

    I recently got my OWON DS6062V 60Mhz scope.
    The manual looks decently translated but I still don't fully trust it so I'd rather ask the more experienced members here.

    My first question is about the maximum input voltage that a scope can take.
    On the front end of the scope it say's 400V CAT II. The probes are rated at 200V @ 1x and 600V @10x.

    Am I to assume that the scope can actually handle 400 volts of input?
    If I'm measuring say 400V with 10x division the scope is seeing only 40V right? So theoretically if I am using high voltage probes set at 10x I could measure say .. 2kV and the scope would see only 200V which would not be a problem.
    (Assuming I am using high voltage probes that can handle 2kV)

    My second question is concerning the ground. As I found out , the probe ground is electrically connected to the main ground which means that when I'm doing measurements I have to stick the probe ground to GND otherwise I can cause a short. Is this because the scope (and my bench psu) is using an SMPS? Would the ground be isolated if say the scope was running off a linear PSU ?

    Thanks in advance.
     
    Last edited: Jun 22, 2014
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,766
    928
    Only an isolation transformer can lift the ground ref from the scope. If a power supply has the three prong plug you can be pretty sure it will carry ground ref.

    This problem is the number one reason battery powered scopes are useful.
     
  3. Shagas

    Thread Starter Active Member

    May 13, 2013
    802
    74
    Hmm so what you are telling me that respectable higher-end scopes like Rigol and Agilent have un-isolated grounds?
    What is the difference between an isolation transformer and a normal step-down transformer? (besides the 1-1 ratio)

    In any case I came up with an idea how I might be able to measure any signal between any two points , and that is by using both channels to measure the single points , and using a subtract function to give me the differential signal. Is that how it is usually done?
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,766
    1,099
    Your 10x probes are rated 600V, so not suitable for 2kV :eek:
     
  5. Shagas

    Thread Starter Active Member

    May 13, 2013
    802
    74
    Well yes , I forgot to mention that 'assuming I was using high voltage probes' :)
     
  6. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,766
    928
    A 'good' scope may or may not have its signal ground tied to its power supply section ground.

    Perhaps this is one of those situations where you pick up and apply an ohm meter and find out???

    Isolation transformers, as the name implies, are designed to 'lift' any ground signal referred to the power supply. Almost any transformer can be made to isolate equipment from mains ground, but this leaves the equipment floating with respect to ground and can be very dangerous should a fault occur. fuses that don't blow and breakers that don't trip to protect one from lethal voltage.

    Better to be sure about your scope. Apply that ohm meter and find out. may not need anything at all.

    using two channels is a normal work around, as is the battery operated type scopes.
     
  7. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
    1,605
    Don't depend completely on that ohmmeter reading. I was just using an "isolated scope" where the isolation was good for voltages up to 40 volts.

    So while galvanically isolated, it wasn't very.
     
    Shagas likes this.
  8. Shagas

    Thread Starter Active Member

    May 13, 2013
    802
    74
    You misunderstood. I have already confirmed with my DMM that my scope is not isolated. I was just asking if it's the same on higher-end scopes.
    In any case thanks for the input.

    "can be made" ? What do you mean by that . Am I correct in understanding that every transformer DOES isolate the ground but due to safety reasons we reconnect the ground back to main ground?

    Edit: So an isolation transformer would be an intermediate stage where the device contains only 2 prongs and double insulation?
     
  9. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    some scope makers provide diferential inputs and isolated inputs, the ground clip on your scope probe is to make sure you hae a good ground refference at the point of test. the farther you get the probe and its ground apart, the more noise and spurious signals you will see.
     
Loading...