I got two 10x probe with DSO. I need to analyze 200-300v waveform which is not possible with the existing 10x probe. Any solution of this?
Add external voltage divider. For example 910 kilo-ohm resistor and 100 kilo-ohm resistor to give 1:10 divider.
Be aware that the DSO is not isolated, i.e. never connect the ground clip to a high voltage.
Thanks a lot for your reply. What is the internal resistance of DSO203? What is the impact of adding this voltage divider in effective internal resistance?
The resistance at the input socket is 1M. A 10x probe has a 9M series resistor giving a total of 10M so would have minimal impact on an external divider with 100K source.
The Quad is specced at 400V p-p when used with 10x probe or 80v p-p with a 1x.
Obviously one needs to take extra care when dealing with high voltages, particularly with respect to the grounding. I like to get everything set up first and keep my hands well clear until power is applied and I can see what is going on.
I bought MCX Plug male jack to make probe. I can make 100x probe using 9.9M series resistance an 100k parallel to input. Is it okay?
Sounds fine to me. Just be careful with insulation, so that the high voltage won’t spark anywhere.
If you can make it 110K instead of 100K for the lower part of the tap then that will make it more accurate 100:1 as the 110K in parallel with the 1M of the scope will be very close to the 100K.
Note also that capacitance around the 9.9M will effect frequency response. The compensation adjustments in the scope adjust for that for normal probes but may not be right for a self-made one. That may not be a concern if you are only interested in relatively low frequencies.
I need to check high voltage (650p-p) waveform about 50Hz to 50k/100kHz
Same technique (external divider) should work. You can measure up to high frequencies providing either the stray capacitance around your external divider is very small or it is compensated. With a 10M resistor at 100kHz then even 0.1pF is enough to seriously affect the measurement and many resistors of that value will have that amount of self-capacitance inherently.
If your measurement point can be loaded a bit then you can help the frequency response by lowering the resistor values of your divider. E.g. a 2.2M / 22K. You can’t take this too far without either loading your circuit too much or increasing power dissipated in your divider. With 325V (1/2 650 p-p) and 2.2M that is less than 50mW so normal power rating resistors would be OK. So with say 0.5W resistors you could lower the values a bit further if it doesn’t load your measurement too much.
If you do need to compensate then this would normally be done by using a variable trimmer capacitor across the lower part of the divider. You may be able to avoid this by re-trimming with the ones built into the dso using a test square wave into your external divider, but you would then need to re-adjust when you went back to normal probes.
The reason why you can’t safely go the 800v which one might think one could do with a 10x probe and a 80V limit at the scope is because the probes themselves have a max voltage rating which is typically around 400 - 500V volts to ensure there is no flash-over.
Either way you want to get your divider and measurement set up all in place before any power is applied and keep your body parts out of the way when powering up. The other thing to be very careful about with high voltage circuits is that capacitors in the equipment can retain a nasty amount of energy long after the power is removed. If you suspect this is the case then be extra vigilant in moving any probes around even with the power off.
Thanks a lot bobtidey.
Can I buy a 100x probe for my DSO203? If yes, from where I can buy? Is there any ready made probe available like other BNC connector probes?
You can use a normal 100x probe and a BNC to MMCX adapter:
ebay.com/itm/Two-250MHZ-Osci … 3ef2553a65
ebay.com/itm/BNC-female-jack … 2326e9848d