[SI-LIST] Re: high frequency current measurements

Hi Junfeng,

You also need to consider the parasitic electric field response of the 
current probes and the impedance level of the circuits. Some of the CT 
series (not sure if all) have significant electric field response. In 
one case where a friend of mine was taking data for a paper, the 
electric field response resulted in a 25% error. I have seen other 
current probes with a 50% E field error on ESD measurements. Look at 
the following papers/articles on my website:

http://emcesd.com/pdf/iprobe98.pdf
http://emcesd.com/tt061999.htm
http://emcesd.com/tt2005/tt050105.htm

Also, I believe the CT-1 (physically similar to CT-6 I believe, but 
not sure) has 1.5 pf of capacitance from the signal wire to the probe 
body. This is about 100 Ohms of Xc at the probe's upper frequency 
limit. It is not unusual to see 30% of the signal current diverted to 
the probe cable because of probe to wire capacitance at frequencies of 
1 GHz so both this capacitance and the circuit impedance are important.

Doug

Xilei Liu wrote:

> Junfeng,
> 
> I think you can find the answer in the operation mannuals. Firstly, you need 
> to check the frequency band of these equipment  to make sure that they are 
> suitable for your use. Then find the transfer impedance (Zt)of the current 
> probe which I think should be provided in the mannual. If some other 
> correction factors are not specified by the mannual, generally, the current 
> can be obtained from the voltage you measured with the oscillosope by the 
> relationship I=V/Zt in linear scale, or I=V-Zt in dB.  All equipment 
> manufacturer websites provide technical support for their products.
> 
> Regards,
> Celine
> 
> 
> 
>>From: "jun feng" <junfeng.zhou@xxxxxxxxx>
>>Reply-To: junfeng.zhou@xxxxxxxxx
>>To: "SI freelist" <si-list@xxxxxxxxxxxxx>
>>Subject: [SI-LIST] high frequency current measurements
>>Date: Mon, 24 Jul 2006 20:53:13 +0200
>>
>>Hi  ,
>>  I am doing some high frequency current measurements. What now I have is
>>the CT6 current probe and a oscilloscope. Is it enough to make the test
>>set-up ?
>>
>>  My question is that usually the oscilloscope is used only for the 
>>voltage
>>measurement, not for current ? how can I deal with it ?
>>
>>  thanks ,
>>
>>
>>best
>>
>>junfeng
>>
>>
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> 
> 
> 
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