LC induction Heater configuration

[ThinkSnow]

I am analyzing a small induction heater that I have tuned to approximately 50 ohms at the operating frequency. I tuned it using the the scalar plot progressively adding to the parallel capacitance. There may be some issues with this tuning approach as I think the resistance of the part being heated may change under power due to the relation between the skin effect and current/power density. I am still working to understand this processt. 
My primary question is how to understand the information reported in the single frequency. The circuit is a parallel LC configuration with the following parameters as measured with the components desoldered using an LCR meter. .210uH, 3166pF The heated part is fixed in the the coil which introduces a resistance to the coil, and significantly drops the Q factor. 


Here is what the Scalar Plot looks like:
This is what I get for the single frequency calculations.  I expected similar numbers to the components, but these are very different. Using the actual component values, I expect a resonant frequency of 6.17Mhz. Is this analysis approach not appropriate despite the fact that the schematic looks the same as my circuit, or I may have a missed understanding of how this is supposed to work. 

 

[matthe...@gmail.com]

Sorry, there were some odd text alignment issues with the inserted images.

On Tuesday, January 31, 2017 at 7:59:01 PM UTC-5, ThinkSnow wrote:

I am analyzing a small induction heater that I have tuned to approximately 50 ohms at the operating frequency. I tuned it using the the scalar plot progressively adding to the parallel capacitance. There may be some issues with this tuning approach as I think the resistance of the part being heated may change under power due to the relation between the skin effect and current/power density. I am still working to understand this processt. 

My primary question is how to understand the information reported in the single frequencyThe circuit is a parallel LC configuration with the following parameters as measured with the components desoldered using an LCR meter. .210uH, 3166pF The heated part is fixed in the the coil which introduces a resistance to the coil, and significantly drops the Q factor. 

Here is what the Scalar Plot looks like:
This is what I get for the single frequency calculations.  I expected similar numbers to the components, but these are very different. Using the actual component values, I expect a resonant frequency of 6.17Mhz. Is this analysis approach not appropriate despite the fact that the schematic looks the same as my circuit, or I may have a missed understanding of how this is supposed to work. 

 

[Melchor Varela]

Hello Matthew,

I guess you realized in the Model screen that the device detects that the calculations are not accurate "Model could be wrong!". The issue is that this automated feature is not able to resolve the equivalent circuit model for all conditions, such in this case where there is a parallel capacitance added to the parasitic inductor capacitance for tuning. I designed this feature mostly for HF RFID coils and inductors with similar characteristics, but it cannot be used broadly.

Best regards,

Melchor

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