Evaluating measurements

[atferrari]

I programed a PIC 18F to generate pulses going from 120 to 6000 Hz.

Measured the output with two frequencimeters (ME and WA) plus the reading from an analog TRIO scope.

In the Excel file I listed following values:

PIC: frequency expected at the PIC's output.
WA: frequency values obtained with frequencimeter WA.
ME: frequency values obtained with frequencimeter ME.
TRIO: frequency calculated from the readings (which also listed).

Readings approximated to 0.25 of a division. Scope is analogic so I had to actually read the divisions in the mask.

On the right I listed the differences between PIC value and the three instruments.

The x axis of the graphic helds PIC values. The curves, the three differences above.

My conclusions, rather limited, besides that all my instruments are of poor quality:

a) PIC could be not producing the expected frequency. (But MPSIM, with current software, allows to think that I am getting the best of it with values close to the Hz in all cases).

b) I am very bad at reading my scope.

c) Frequencimeter ME is worst than WA. (Both frequencimeters are of the type embeded in garden variety multimeters).

Do you have more useful / educated conclusions to make? I will appreciate that.

Attached file here

http://www.mediafire.com/?5m4renbezsy

Agustín Tomás

 

[MacGyverS2000]

I'm not going to download a file of unknown origin... how about taking a screen capture and posting it.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[itsmoked]

I would think your FREQUENCY METERS are the problem. The cheap DMM meters can be way off and can be confused by square waves.

PICs usually are right on. If you know what frequency the crystal is.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[atferrari]

Hola Dan,

That will make for ANOTHER file of unknown origin. No thanks.

Hola Keith,

Thanks for replying. For both multimeters, square wave IS acceptable according to their user manual.

My mistake (?) is to show round figures for PIC. Actual difference, at least in theory, is fraction of a Hertz for all values. (Nothing serious, anyway, I think). Software was writen to ensure that.

Agustín Tomás

 

[MacGyverS2000]

Browsers will open a JPEG or GIF without compromising system security... I can't say the same for a downloaded file, even if it is Excel. Your call...

How far off is the frequency? Have you set up the timers correctly?


Dan - Owner

http://www.Hi-TecDesigns.com