Test and Measurement Forum

3425

Post any questions you may have about our current range of USB data loggers

3425

Postby skyp8ul » Wed Nov 23, 2011 9:41 am

Hi there,

Can I use 3425 to measure voltage directly from Ac power source? (which is 240V or 110V). Will that damage the differential input of 3425?

thanks,
Heng, TP
Penang
skyp8ul
Newbie
 
Posts: 0
Joined: Wed Nov 23, 2011 9:38 am

Re: 3425

Postby Hitesh » Wed Nov 23, 2011 11:24 am

Hi Heng,

Unfortunately, the 3425 is not safety rated to be used for measuring with direct connection to a public utility voltage supply. It is only rated CAT I and you would require CAT II or CAT III rating.

To measure mains voltages, for safety and to comply with legal regulations, you need isolation from the mains which forces you to use either a differential isolating probe or at the very least an isolating transformer of known turns ratio.
The ground lead of a standard probe is connected to the ground of the scope and the ground of the attached PC/Laptop. If that is connected to the live (or even the neutral) of the mains supply there will be a very destructive current surge. If the PC/Laptop is floating there will still be dangerous voltages appearing on the exposed metal parts. Even if the ground is kept separate, it is illegal to connect a (CAT I) scope input directly to mains voltages if it does not have a full mains safety rating (CAT II or CAT III).

What you could actually use is:-

1 of, TA041, active, differential probe:-
http://accessories.picotech.com/active-oscilloscope-probes.html#TA041

1 of, TA011, AC current clamp:-
http://accessories.picotech.com/current-clamps.html

1 of, MI078, BNC to 4mm adapter (scroll to bottom of page):-
http://www.picoauto.com/automotive-test-leads.html

1 off, PS4224, 2 channel oscilloscope:-
http://www.picotech.com/picoscope4000-specifications.html

It might be possible to use a 3425 but you would need a differential probe and a method of converting the signal to a single-ended one.

Please look at the following application note. It uses a different current clamp and scope but is otherwise the same:-
http://www.picotech.com/applications/mains-power-analysis.html

I hope this helps.

Regards,
Hitesh

Technical Specialist
Pico Technology
Hitesh
Site Admin
Site Admin
 
Posts: 2063
Joined: Tue May 31, 2011 3:43 pm
Location: St. Neots, Cambridgeshire

Re: 3425

Postby skyp8ul » Thu Nov 24, 2011 1:42 am

Hi Hitesh,

Thanks for your prompt reply.

My next question is, do we have any data logger that can measure up to DC 36V and AC 150V?

Thanks,
Heng, TP
skyp8ul
Newbie
 
Posts: 0
Joined: Wed Nov 23, 2011 9:38 am

Re: 3425

Postby Hitesh » Fri Nov 25, 2011 9:30 am

Hi Heng,

You may wish to look at the ADC-20 or 24 devices:

http://www.picotech.com/precision-data-acquisition.html

These can measure +/- 2.5V so you would need some kind of circuitry to step-down the voltage safely to that level. You would then have to apply some scaling within the PicoLog software.

Hope this helps.
Hitesh

Technical Specialist
Pico Technology
Hitesh
Site Admin
Site Admin
 
Posts: 2063
Joined: Tue May 31, 2011 3:43 pm
Location: St. Neots, Cambridgeshire


Return to USB PC Data Loggers

Who is online

Users browsing this forum: No registered users and 0 guests