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Thanks, and i suppose we just rap the probe lead a few ties round the torroid?larger high µr toroid cores are much better suited to reduce common mode interferences on cables, something like Epcos/TDK B64290L0082X830.
Thanks, the scope is actually straight into the mains...the led power supply is powered through an isolated AC PSU.I assume your scope is fed through a mains isolating transformer.
Sure, five turns or so.Thanks, and i suppose we just rap the probe lead a few ties round the toroid?
Presume the power supply has considerable output capacitance, isolation for high frequency common mode noise is hardly perfect.Thanks, the scope is actually straight into the mains...the led power supply is powered through an isolated AC PSU.
The ferrite is acting as common mode choke.All scope leads I have seen are coax: you are unlikely to see any significant improvement with a wrap around ferrite.
Thanks yes i see your point.......incidentally, when we raplaced the isolated output AC PSU with a simple Carroll and Meynell 50Hz isolation transformer, the problem still occurred.We can just guess how much high frequency isolation is provided by the "AC output PSU". Probably not much.
Thanks, but it works fine without the coaxial probe attached.In this case, I suppose a design fault of the LED driver causing unexpected susceptibility to conducted or capacitively coupled noise.
Thanks, i did a search for such a 50Hz current sense transformer, or even just the core so we could wind it ourselves, but there is absoluteley nothing off the shelf that isnt stratospherically expensive.Why not use a current transformer on the AC side of the rectifier
Can't take this seriously...Thanks, i did a search for such a 50Hz current sense transformer, or even just the core so we could wind it ourselves, but there is absoluteley nothing off the shelf that isnt stratospherically expensive.
Thanks, thats interesting, when we used the DIY coaxial probe it is a x1 probe and we had the scope set to x1.use 1:10 input so that loading is minimal.
Sounds unlikely if the ground connection goes to the same circuit node in both cases...
Thanks, good point the ground connection of the probe was not to the same place in both cases....there is a ET current limiter, and now i show this in the attached...as you can see, the probe ground is more kind of downstream for the OK measurment of the 14v internal rail.Sounds unlikely if the ground connection goes to the same circuit node in both cases.
This is very bad for us, because when testing the circuit, its nice to be able to clip the scope ground to the circuit ground...
You are using two single ended inputs in A-B mode. There's no CMRR available in this case, just gain matching. The worst point is that the input attenuator must be set according to the expectable "common mode" voltage to avoid overload. I think the method isn't really applicable to measure volts with several 100 V common mode voltage.You use channel A and channel B and see on the scope signal for (A-B) and the probe tip of B connected to circuit ground and use probe tip A to test various points of interest.
As long as your scope input amplifier has some decent CMRR, this will work fine; just leave the ground connections of both the probes hanging.
The design is a bit unusual. Most HV probes have 4 mm safety jack plugs, so you can connect anything, e.g. test tips. I would replace it.our TA041 diff probe just has two croc clips which are very slow to use when you need to quickly examine multiple circuit nodes.
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