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Multisim Measurement Probe Error

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Hello,

I have assigned an AC circuit problem to my students.  They are to measure voltage and current values with magnitude and phase.  It appears that some of the results are incorrect.  The circuit with results is attached and the correct answers are below.

 

 

I made similar measurement with the FG and scopes and it is correct.

 

                       

 Is = 943<33.61° mA                 I22nF = 849<59.36° mA             V3k =  1.23<-30.64° V

I3k =  410<-30.64° mA

 

 

 

Carlotta Berry
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Accepted by topic author carlottaberry

Hello,

 

You are using a Probe in reference to another probe to calculate the phase at that point. This has a limited functionality as it only gives the Voltage phase. If you simply put down those probes without reference, you'll notice:

 

1. The Irms and Vrms are correct in this case.

2. The phase won't be shown.

 

This is due to the fact that the reference probe calculates a difference. In the case of the current through the 22nf Cap, you'll notice the pahse is 30.8. This is because that's the difference in phase of the voltage (which is the same for both I22n and I3k) compared to the one coming from the source. This is calculated as Referenced Probe - Probe. If we were to divide using a calculator phase of V by the impedance at 22n then we'd obtain the correct current.

 

The phase calculation is of limited functionality in Multisim.

 

Kind Regards,

Miguel V
National Instruments
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Thanks Miguel for your thorough reponse, that does help!

 

I had discovered that I could get the correct magnitudes for the voltages and currents when I removed the phase but was not sure why.

 

So when would I ever use the phase measurement on the probe?  Can you give me an example?

 

Thanks.

 

Have a great day.

Carlotta Berry
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Hello,

 

I have sent you an email discussing this. The phase measurement on the probe is simply a differential measurement in phase between two points. So you can use it, if you want to find the voltage phase difference between two points, or the current's by using a current probe. However, all the other variables in the probe will also be a differential. Meaning that the difference in voltages and currents and all other parameter's will be (for the most part) different.

 

Kind Regards,

Miguel V
National Instruments
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