Could not measure speed signal using ECAP module.

Swanand Pisat

Other Parts Discussed in Thread: TMS320F28335

I am trying to measure the speed of motor using ECAP module of TI in matlab. I am able to measure frequency of PWM signal which I am generating though my board itself. But when I apply speed sensor signal, the module is not able to measure the frequency of applied speed signal.

I have made different logic for edge and then frequency detection and that logic is giving me good results. But still I believe those results are not accurate enough for me and I want to measure signal frequency through ECAP only.

Can anyone help me to trace out where the problem would be?

Environment details:

Controller: TMS320F28335

Code generation through MATLAB-Embedded Coder-CCS

IDE- CCS3.3

over 7 years ago

0 Brett Larimore over 7 years ago

TI__Guru 57255 points

Hi,

Is the speed sensor's output a square-wave? The eCAP needs its input to be digital.

What does 'not able to measure' mean?

Thank you,
Brett

0 Swanand Pisat over 7 years ago in reply to Brett Larimore

Prodigy 70 points

Speed sensor output is open collector and we have pulled the output as 0-3v square wave.

What I mean by saying not able to measure is that, output of ECAP module is not stable. It is giving erroneous output.

0 Brian McKay over 7 years ago in reply to Swanand Pisat

Mastermind 9005 points

What version of MathWorks tools are you using? Did you try one of the examples we provide, and does that work correctly?

-Brian

0 Swanand Pisat over 7 years ago in reply to Brian McKay

Prodigy 70 points

Hi,

We are using Matlab 2012b. and as described in the query, we were able to measure frequency of PWM signal generated from our evaluation board correctly.

Is there any problem in the signal that we are measuring? If it is so then how could we able to measure it through our GPIO logic?

-Swanand

0 Swanand Pisat over 7 years ago

Prodigy 70 points

The speed signal that we are measuring looks like shown in the picture.

Displaying DSC_3966.JPG

0 ejs over 7 years ago in reply to Swanand Pisat

TI__Intellectual 2930 points

Dear Swanand,

let me attach your screenshot again. Can you please provide more details about the signals below? Can you describe your setup? Where do you measure these signals?

Can you resolve the problem when you apply a clean signal at eCAPx?

0 Swanand Pisat over 7 years ago in reply to ejs

Prodigy 70 points

As shown in the screen shot, the upper one signal(Yellow) is the signal which we are getting from Speed (hall) sensor and the signal which is shown below(blue) is the 'conditioned signal' of speed sensor.

We have tried using ECAP for frequency measurement by applying both signals but neither giving proper output.

We are measuring these signals at the motor shaft using a hall sensor.Hall sensor output is open collector and we have pulled the output as 0-3v.

We could able to measure the frequency using ECAP if we give PWM signal generated from our board itself.

0 ejs over 7 years ago in reply to Swanand Pisat

TI__Intellectual 2930 points

Please have a look at the spikes of your signal. Can you share a measurement that show these spikes in more detail, i.e. size, width?

You also might want to check www.ti.com/.../sprufb0d.pdf about muxing and qualifiers. For example you can try to apply a Qualification Using a Sampling Window (www.ti.com/.../sprufb0d.pdf.

C2000™︎ microcontrollers

C2000 microcontrollers forum

Could not measure speed signal using ECAP module.