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Registered Member #1339
Joined: Wed Feb 20 2008, 04:43PM
Location:
Posts: 9
Dr. Slack wrote ...
Rather than draw any diagrams myself, here is one source from picotech There isn't a bandwidth to predict with a correctly compensated divider, it's flat from DC to light, well, from DC to well above your 5kHz requirement until other non-ideal things bite.
It's not the one you are using as it's +/-5v input, but the NI 9234 four channel diff input module is 305kohm differential input impedance. I'm not going to flog through all the NICompactDAQs seeing which one is 4 channel 10v, it's usually polite if you have a piece of kit in mind to give the part number, rather than set a puzzle for responders.
I doubt you will get very wideband performance from this DIY Oscope probe without the "lossy" coax used by most if not all manufactures. The original P6015 HV probe from Tektronix used a resistive center wire of around 50 ohms / foot.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
Just a few thoughts based on my time in the UK rail industry (+/- a few memory problems)
If taking power from the overhead line (3 kV dc in Spain I think, unless something new to me) (or totally scary 25 kV rms as here also) there are so many safety issues, e.g. I have a box of 0.5W VR37 resistors commercial rating 3.5 kV, UL rating 250 V ! or very special high rupture current fuses are required .. costly etc. more modern components may be better BUT you should have a record of your verifying the 'safety rated' voltage with supplier or manufacturer of any component used, mention it is for Railway use, more precise information usually freely given (potential $$$$$)
Given the overall cost (components, time ...) if this is just a one-off then maybe the safe route is something like would give 10 V out for 1 kV in,
if you still want to DIY then MASSIVELY over rate your components. so, for safety, you could copy a design for a 25 kV rated home-brew probe.
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Voltage divider for up to 1500Vdc 5kHz BW
