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Picoscope 2204 & circuits switching inductive loads

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Picoscope 2204 & circuits switching inductive loads

Postby Mike_T » Thu Nov 29, 2012 8:13 am

Hi, I'm a newbie who has bought a Picoscope 2204. One of my planned applications is to measure voltages in a circuit supplying pulse-width modulated power to a 12V brushed DC motor. I am concerned about the potential damaging effects on the scope of the fly-back voltages generated by rapid switching of 12V through an inductive load. Are there any precautions that I should take to protect the Picoscope?

On this occassion the switching MOSFET has inbuilt protective Zener diodes and I have added a power diode across the motor. Is this sufficient to protect the scope and could thw scope be used even if these diodes were not present?

Thanks, Mike
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Re: Picoscope 2204 & circuits switching inductive loads

Postby PeterF » Fri Nov 30, 2012 8:33 am

Hi Mike,
While the protective diodes may well protect the scope that cannot be guaranteed in all conditions. To be safe, you really need to use x10 probes to connect to the motor. You can use the standard MI007 x1/x10 probe that we sell for the 2204:-
http://accessories.picotech.com/passive-oscilloscope-probes.html#MI007
These allow measurement up to +/-200V and protect up to +/-600V when switched to the x10 range.
Regards,
PeterF.
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Re: Picoscope 2204 & circuits switching inductive loads

Postby Mike_T » Fri Nov 30, 2012 11:28 am

Hi Peter

Thanks very much for that guidance.

The probes I bought were designated PP787 but I see that the leaflet enclosed with them mentions the code M1007 so I guess I do have the probes that you refer to.

Regards, Mike
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Re: Picoscope 2204 & circuits switching inductive loads

Postby PeterF » Mon Dec 03, 2012 4:02 pm

Hi Mike,
In that case, make sure that you use them in the x10 setting. For best results, also trim them for HF response:-
http://www.picotech.com/applications/how-to-tune-x10-oscilloscope-probes.html
Regards,
PeterF.
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