reading resolver with pci-6052e

[Peter B]

Dear all,

I am not so experienced yet in labview and I thought I had a simple measurement problem which I could solve, but things seems a little bit more difficult and i desparately could use a little help and suggestions from you guys (and girls)!

The situation:

I have: pci-6052e, labview 7.1

I want to measure the angle and speed of a motor with a resolver. 

Measuring setup:

one analog output generates a sinus waveform of 7kHz, 7 volt,  and drives the resolver excitation winding (through a buffer amp, schematic available if you need). We did not have budget for scxi 😞  but this amplifier is working well.

two analog inputs measure the two windings. By taking the atan2 (ai0/ai1) of both signals I get the absolute position of the rotor. 

So far it seems simple to me. I am able to generate the sinus waveform (Cont Gen Voltage Wfm-Int Clk-On-Board Regeneration.vi)  

The problem

To get a measurement with high signal/noise ratio I want to measure the analogue inputs at the same time that the sinus of the generated wave is at its peak - at the top of the sinus. At that particular moment the two analog inputs will also have the highest input and I can make a accurate reading.

The problem now is how to synchronise the excitation and measuring so that I take one sample at a frequency of 7kHz at the same time as the excitation peaks. I do not know how to realise this.

After calculating the angle I need to calculate the speed by taking the derivative of the angle. For this the angle signal needs to have the timing with it (need dt). After taking the atan2 I have only a float available. How do I get the time with it? can I in some way use the 1/7kHz time interval?

Any help and suggestion would be most welcome!

Peter

[Laura F.]

Hello Peter,

Would it be possible for you to acquire all of your analog input data and after it is acquired, find the point that matches up with the peak of your wave?  It seems that this would be an easier solution than trying to only acquire one point of data at the same exact time your output wave is at its peak.   

As for the derivative calculation you are describing, it seems you need the time between the two successive analog input measurements you are using to calculate the derivative.  You will calculate two different angles based on the arctangent you described so for the dt, I would guess you use the time difference between these two points.  And if the points happen once each period of the wave you generate, then it would indeed be 1/7KHz. 

Let us know if this helps!

Thanks,

Laura

[Peter B]

Thank Laura!

Good idea, this will make things much easier. I am able to measure the angle know, the next thing I need to make is speed calculation but that is not to difficult know because the timing info is available in the wave form.