Searching \ for '[EE]: measuring jitter on a scope' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/index.htm?key=measuring+jitter
Search entire site for: 'measuring jitter on a scope'.

Exact match. Not showing close matches.
PICList Thread
'[EE]: measuring jitter on a scope'
2002\08\22@112705 by Bob Japundza

flavicon
face
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.


2002\08\22@121000 by Jim

flavicon
face
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 removed}

2002\08\22@121011 by Robert E. Griffith

flavicon
face
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}

2002\08\22@122832 by Bob Japundza

flavicon
face
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}

2002\08\22@133228 by Jim

flavicon
face
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.JapundzaTakeThisOuTspamREALMED.COM>
To: <.....PICLISTKILLspamspam@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}

2002\08\22@133646 by Bob Japundza

flavicon
face
Thanks, Jim, I'll give it try tonight.  Yes, the gyro is a single-axis unit.

Bob

{Quote hidden}

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2002\08\22@202148 by Peter L. Peres

picon face
On Thu, 22 Aug 2002, Bob Japundza wrote:

>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

You want to get rid of the sine wave and just use the DC component. The
sine wave is noise from the synchronous rectifier inside the gyro, not
your useful signal. Your useful signal is 2mV/deg/sec afair and it drifts
up to ten times as much with temperature and the time of day and the
course of the yen. Murata and Tokin have app notes for their gyros. How
about taking a look ? Probably then one for the make you are using ?

Peter

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2002\08\22@214954 by Peter L. Peres

picon face
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.


More... (looser matching)
- Last day of these posts
- In 2002 , 2003 only
- Today
- New search...