Post by thread:[EE]: measuring jitter on a scope

I am working with a piezo gyro that puts out a bit of noise/jitter in its output. I have a couple of different op-amp filter circuits I've thrown together to see how well they clean up the output of the gyro, but at the same time not screw with the bandwidth of the gyro's output. The gyro puts out approximately 2.5v at a steady state, and goes up/down from there depending on the direction of rotation. I have been trying to measure the noise level of the output with my scope without success; I assume it is because I don't have anything to trigger off of. My guess is that I need a function generator (which I don't have at the moment, but one is on the way) tied into the external trigger input of the scope and "sample" that way. Can anyone tell me that I'm correct in my thinking? What frequency should I use to sample the output? Also, it seems my scope is a bit out of calibration (Tek 475). I have just located some manuals on ebay; is it difficult for one to calibrate this scope, or should I be looking to send the scope off somewhere to be calibrated? thanks, Bob -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

I am a relative beginner at scopes so take all this with a grain of salt. (BTW I bought a Tek 475 off ebay about 18 months ago. I like it). You can trigger the scope of the 60 hz power line (similar to using a function generator at 60 hz), but your signal will not be correlated to the external trigger so I don't think it will be much use. (but try it, and see what you can see). My guess would be to try to get the gyro to produce a periodic signal. You could put together a little rig that would move the gyro back and forth at a constant rate. Something like a cam on a drill (or other) motor in contact with a board the the gyro is attached to. Use gravity or a spring to keep the board in contact with the cam. Or use a rod - one end pivot attached the the gyro assembly, the other pivot attached to a spinning disk. Or, double side tape the gyro to a washing machine and put it in spin mode with an unbalanced load :) With a period signal form the gyro, you will be able to sync up and get a close up picture of a small signal. --BobG {Original Message removed}

Okay. These scopes have actually three trigger modes as determined by the "Trig Mode" push buttons: Auto - sweep with or without trigger signal. (results similar to the old recurrent-sweep scopes like the EICO 460! and old Heaths) Norm - the scope -only- sweeps with tgiggering signal criteria being met Sngl Swp - Single sweep Also, you can choose your trigger to be DC or AC - and the AC mode has like a 20 Hz or so low freq cutoff. So, I would choose DC. By careful adjustment of the "A Trigger" "Slope" and "Level" control you should be able to trigger off a slow-moving waveform as it crosses the trigger threshold. Also, be sure to choose "DC" coupling on the switch located below the rotary "Volts/Div" switch on the channel you're working with! Next question - is this just a one-axis gyro (I've not played with the recent crop of piezo gyros, my expereince was with the mechanical stuff a few years back). RF Jim ----- Original Message ----- From: "Bob Japundza" <spam_OUTBob.JapundzaTakeThisOuTREALMED.COM> To: <.....PICLISTKILLspam@spam@MITVMA.MIT.EDU> Sent: Thursday, August 22, 2002 11:26 AM Subject: Re: [EE]: measuring jitter on a scope Jim, I have set it as you describe and have no idea why it isn't triggering. The dc output of the gyro is proportional to rate acceleration, approx 20mv/deg/sec. I do get some sine waves on the display, but when I rotate the gyro I don't see any change in amplitude. Bob > {Original Message removed}

Thanks, Jim, I'll give it try tonight. Yes, the gyro is a single-axis unit. Bob {Quote hidden}> -----Original Message----- > From: Jim [jvpollKILLspamDALLAS.NET] > Sent: Thursday, August 22, 2002 12:33 PM > To: .....PICLISTKILLspam.....MITVMA.MIT.EDU > Subject: Re: [EE]: measuring jitter on a scope > > > Okay. > > These scopes have actually three trigger modes > as determined by the "Trig Mode" push buttons: > > Auto - sweep with or without trigger signal. > (results similar to the old recurrent-sweep > scopes like the EICO 460! and old Heaths) > Norm - the scope -only- sweeps with tgiggering signal > criteria being met > Sngl > Swp - Single sweep > > Also, you can choose your trigger to be DC > or AC - and the AC mode has like a 20 Hz > or so low freq cutoff. > > So, I would choose DC. By careful adjustment of the > "A Trigger" "Slope" and "Level" control you > should be able to trigger off a slow-moving > waveform as it crosses the trigger threshold. > > Also, be sure to choose "DC" coupling on the switch > located below the rotary "Volts/Div" switch on the > channel you're working with! > > Next question - is this just a one-axis gyro (I've > not played with the recent crop of piezo gyros, > my expereince was with the mechanical stuff a > few years back). > > RF Jim > > > ----- Original Message ----- > From: "Bob Japundza" <EraseMEBob.Japundzaspam_OUTTakeThisOuTREALMED.COM> > To: <PICLISTspam_OUTMITVMA.MIT.EDU> > Sent: Thursday, August 22, 2002 11:26 AM > Subject: Re: [EE]: measuring jitter on a scope > > > Jim, > > I have set it as you describe and have no idea why it isn't > triggering. The > dc output of the gyro is proportional to rate acceleration, approx > 20mv/deg/sec. I do get some sine waves on the display, but > when I rotate > the gyro I don't see any change in amplitude. > > Bob > > > -----Original Message----- > > From: Jim [@spam@jvpollKILLspamDALLAS.NET] > > Sent: Thursday, August 22, 2002 11:01 AM > > To: KILLspamPICLISTKILLspamMITVMA.MIT.EDU > > Subject: Re: [EE]: measuring jitter on a scope > > > > > > Bob, > > > > Can you explain why it is you have nothing to > > trigger off? > > > > I am assuming you can simply set the scope's trigger > > Source for CH 1, set for AC, adjust the level and get > > triggering ... > > > > What is the output of the piezo gyro supposed to be? > > > > Is it DC proportional to something? > > > > I've got a 475 too, and the Horz scale is shrunk ... > > > > RF Jim > > > > > > ----- Original Message ----- > > From: "Bob Japundza" <RemoveMEBob.JapundzaTakeThisOuTREALMED.COM> > > To: <spamBeGonePICLISTspamBeGoneMITVMA.MIT.EDU> > > Sent: Thursday, August 22, 2002 10:25 AM > > Subject: [EE]: measuring jitter on a scope > > > > > > I am working with a piezo gyro that puts out a bit of > > noise/jitter in its > > output. I have a couple of different op-amp filter circuits > > I've thrown > > together to see how well they clean up the output of the > > gyro, but at the > > same time not screw with the bandwidth of the gyro's output. > > The gyro puts > > out approximately 2.5v at a steady state, and goes up/down > from there > > depending on the direction of rotation. I have been trying > > to measure the > > noise level of the output with my scope without success; I > > assume it is > > because I don't have anything to trigger off of. My guess is > > that I need a > > function generator (which I don't have at the moment, but one > > is on the way) > > tied into the external trigger input of the scope and > > "sample" that way. > > Can anyone tell me that I'm correct in my thinking? What > > frequency should I > > use to sample the output? > > > > Also, it seems my scope is a bit out of calibration (Tek > > 475). I have just > > located some manuals on ebay; is it difficult for one to > > calibrate this > > scope, or should I be looking to send the scope off somewhere to be > > calibrated? > > > > thanks, > > > > Bob > > > > -- > > http://www.piclist.com hint: The PICList is archived three different > > ways. See http://www.piclist.com/#archives for details. > > > > -- > > http://www.piclist.com hint: The PICList is archived three different > > ways. See http://www.piclist.com/#archives for details. > > > > > > > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

On Thu, 22 Aug 2002, Bob Japundza wrote: >I am working with a piezo gyro that puts out a bit of noise/jitter in its >output. I have a couple of different op-amp filter circuits I've thrown >together to see how well they clean up the output of the gyro, but at the >same time not screw with the bandwidth of the gyro's output. The gyro >puts out approximately 2.5v at a steady state, and goes up/down from >there depending on the direction of rotation. I have been trying to >measure the noise level of the output with my scope without success; I >assume it is because I don't have anything to trigger off of. My guess Hang the gyro on a pendulum with fairly short period (1 second or less). This if you lack a shaker table with twist mode. You can make a pendulum easily. You can also build a proper table using a speed regulated motor to drive its end through a pushrod. Make sure it works smoothly. The pendulum is FAR simpler to make and needs no motor. You will have several tens of seconds to do measurements and you can deduce the sensitivity and other things very accurately (if you use something accurate to find the period - like a single photodetector and measure the time for both sides of the movement). The same detector can also measure pendulum speed (since the beam interrupter is of finite size), which gives amplitude, which gives maximum angle which allows you to compute sensitivity etc etc. Peter -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.