pulse width triggering

by **kintech** » Sat May 25, 2013 5:05 pm

I have a PWM signal that I am probing but I have problems getting it to trigger on pulse width triggering. I set it to positive pulse and outside time range and set a time that is less than the size of the duty cycle, but it will not trigger. The only time it will trigger is if I set the time to 0 but if I set to to the next smallest interval 2ns, then it won't trigger anymore.

What is the proper procedure to get it to trigger on pulses larger than a certain size?

by **Hitesh** » Tue May 28, 2013 1:12 pm

Hi Kintech,

Which PicoScope software version and oscilloscope model are you using?

Do you have a .psdata file that shows your setup?

We are aware of an issue relating to Pulse Width Triggering for PicoScope 340XA/B devices which is being investigated.

Thanks,

by **kintech** » Tue May 28, 2013 8:31 pm

I am using 3206MSO and software version 6.7.21.2

I have attached the psdata for the setup I am using. There is a PWM being generated externally but the pulses never trigger even though they are greater than the time specified in pulse width triggering.

by **Hitesh** » Wed May 29, 2013 3:20 pm

Hi Kintech,

I've run some tests using the same version of PicoScope 6 with square waves. I've found that the trigger works using your settings (I changed the trigger type to repeat).

I varied the signal from around 1kHz to 30kHz, and found that above 24kHz, the scope does not trigger as the width of the pulse is 20us.

Just a few things to check:

Click Help -> About PicoScope 6, what is the driver version?
Please ensure your probe is set up correctly - have you adjusted the probe at the x10 setting?
Does the signal appear correctly in terms of amplitude with no trigger?

Regards,

by **kintech** » Sat Jun 01, 2013 1:30 am

The specs for my picoscope is:

Model: PicoScope 3206MSO
Serial Number: CW002/048
USB Version: 2.0
Hardware Version: 1
Driver Version: 1.0.0.404
Firmware Version: 1.3.3.0 / 0.6.6.0

The probe and software are set to 10x and it does trigger properly when the rising edge option is used. My confusion was why the square pulses in my settings don't seem to trigger when the pulses are 45us. Is our driver and firmware matching yours?

by **Hitesh** » Mon Jun 03, 2013 1:46 pm

Hi,

These are the same driver/firmware versions that I am using and it works here if I run the device using your data file which was set to greater than 20us.

I've used a signal generator to test the greater than 2ns and that works.

What is it that you are looking to test. Are you able to show what your waveform looks like when looking for the greater than 2ns condition? What happens if the condition is set to greater than 200ns?

At high frequencies, the waveform may not appear as expected. You can try adjusting the trigger level threshold.

Regards,

by **kintech** » Mon Jun 03, 2013 8:32 pm

I'm trying to catch a transition between two pwm duty cycles so I wanted to use pulse width to trigger when the width of the on time exceeds a certain interval. So the on time may start at 10us and then transition to 30 us, so I want it to trigger on the first pulse that is 20us or greater.

On the attached file is an example of the condition where no trigger occurs. I set the picoscope signal generator to 1kHz which has an on time of 500us but it doesn't trigger on the 20us setting of pulse width. Am I using the trigger settings correctly?

by **Hitesh** » Tue Jun 04, 2013 2:25 pm

Hi,

Please use an alternative source for the signal generator - changes made to the sig gen while the scope is waiting for a trigger will not take effect.

Also do not use Auto trigger as it will time out. I've attached a sample data file that I've captured. You can load it and try running your scope with the settings.

3206MSO_Pulse_Width_Test.psdata: Example psdata file showing pulse width trigger; (79.34 KiB) Downloaded 90 times

Regards,

by **kintech** » Tue Jun 04, 2013 11:06 pm

I have switched to using an external source to generate a pwm. This time I have a 3.3V square wave that has on time of 5ms. I used your downloaded settings and switched my probe to 1x (to match the software settings) and resized the time/div. Everything else is the same as the settings you uploaded previously. However, it still will not trigger.

by **Hitesh** » Thu Jun 06, 2013 4:22 pm

Hi,

Have you tried the same signal and trigger setup on channel B?

Please try the falling edge condition and also some of the other trigger setups such as Window or Window Pulse width.

Have you got another probe you can try?

If this fails, can you please e-mail support@picotech.com

Thanks,

by **kintech** » Fri Jun 07, 2013 11:59 pm

We have tried these suggestions, but we still can't get it to work. I've sent an email to the support address you gave.

Thanks,
Kintech

by **Hitesh** » Mon Jun 10, 2013 8:55 am

Hi,

There is a bug relating to pulse width triggering on the 3000 MSO devices. It has been partially fixed in PicoScope 6.7.27 (RC) which can be downloaded from the website.

A full fix requires a driver update and should follow in a few weeks.

Regards,

by **kintech** » Mon Jun 17, 2013 4:20 pm

The 6.7.27 version works for pulse width triggering. We will look forward to the driver update. Thanks for your help.

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