Problem with high voltages

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21 Dec 2007

I am a little confused: the CS328A can measure 80Vpp voltage. But with a x10 Probe it cuts the signal at 240V Peak when i connect the probe to 230V phase line. The real peak should be at 325V.
If i zoom in to the real peak at about 325V it is shown correct, but i can't see the whole 230V RMS signal...
What is wrong?

Thanks for your time,

21 Dec 2007
Posts: 73

Hello Claudius,
I am not sure where you found the 80V as the maximum input voltage is specified as 20V. Therefore to measure 230V accurately you need to use a 1:100 probe.


3 Jan 2008

hm... on the CS328A Page it sais:
""Gain automatically set from 20mV full scale to 800V full scale by choosing graph view and probe switch setting.""

So i reasoned it had 80Vpp and can measure 800Vpp with 10:1 probes.
How is the information on that pabge meant?!

4 Jan 2008
Posts: 412

Hello Claudius,
sorry, we need to change the manual. The classic CS328 has a range of +/-40V (80V p-p) and is ok for looking at 230V rms. With the CS328A, we traded off maximum range for lower noise on the x10 ranges. The spec is now +/-20V. This means that you will need to use a x100 probe. You may wish to send us an email about this.

1 Nov 2008

Im sure the changes was made to make it more useful and convenient.I think this could help more to the users.But then you will also adjust for the changes made.

24 Feb 2009

I also had the same problem and i'm afraid especially when it comes to high voltages.I'm glad to read your conversations here so that i can have the idea what to do.Please help me!

27 Feb 2009
Posts: 412

Hello cassandra, if you want to look at higher voltages there are two ways to go:
1. Use a differential probe. This is the safest way, as it does not matter which way you connect the probes. We sell two differential probes - the CS1030 good for 1300V, and the CS1031 good for 6500V.
2. Use a 100x or 1K probe. The 100x probe is rated at 1500 V (Cat III), and the 1000x probe at 15 kV (Cat III). However both of these probes have a ground connection which is continuous to the mains earth, and to the USB ground and hence the PC. If you inadvertantly connect the ground clip to a live connection you will need a ground fault interrupter (GFI) or Residual Current Device (RCD) to turn off the mains supply to protect both yourself, and the equipment.

In fact we highly recommend having a GFI or RCD in your mains supply any time you are working with high voltages.
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