suggest basic func/signal generator for basic scope test/setup ?

[robb]

there is quite a variety of sig/func generators on the bay ...
just wondering if there is a basic series or brand to looking for
to test/setup a tek 2236 scope ?
thanks
rob

 

[Tony Hwang]

there is quite a variety of sig/func generators on the bay ...
just wondering if there is a basic series or brand to looking for
to test/setup a tek 2236 scope ?
thanks
rob

Hi,
You have a built-in calibrator in the 'scope. One I'd like will be
multi wave form capable with variable frequency and out put level.
If your set up means calibration, then the generator should be
calibrated against known reference as well. I send in my 'scope
to a lab to maintain it's calibration official.

 

[JeffM]

there is quite a variety of sig/func generators on the bay ...
just wondering if there is a basic series or brand to looking for
to test/setup a tek 2236 scope ?

http://www.google.com/images?q=Fluke-5820A

How are you planning to verify that the crap you buy on ebay
is giving a valid output?
Anything without a recent NIST-traceable certificate
is only adding more variables to your situation.

If you have doubts about the accuracy of your scope,
take it to a metrology lab
for calibration with NIST-traceable standards.

 

[mike]

there is quite a variety of sig/func generators on the bay ...
just wondering if there is a basic series or brand to looking for
to test/setup a tek 2236 scope ?
thanks
rob

You need to be a lot more descriptive about what you're trying to
accomplish.
If you have other uses for the generator, use those criteria for your
decision. If ALL you want is to calibrate the scope, forget it.

For calibration purposes, a generator won't do you any good unless it
has the waveform precision you need and also has traceable
calibration. You can't afford that.

It's a binary situation. If you use your scope in business, and
maintain any certifications, you must send it in to have it done right.

For hobby use, my experience says that a TEK scope either works "close
enough" or it needs fixed. A scope is a poor tool for making
measurements. It's great for "looking at the waveform", but unless
you have a scope with built-in counter and DVM, you won't get accurate
measurements.

Here's how you check a scope.
If it's a CRT scope, there are some things that mess up everything.
Wrong high voltage can shrink or expand the display. A sure sign
is if the display changes size when you change intensity. Make sure
that's not a problem before you go tweeking stuff. Ditto for
other power supplies, but the effects can be much less dramatic.

Do all the functions work? check.
Does it trigger? check.
Use a T-connector to put your DVM and a variable power supply into the
vertical input. Compare deflection against your DVM. Check
Stick a transformer from the AC line into the input. Wall wart etc.
Does it look like 60 Hz. or 50Hz. depeding on where you live.
You can check several sweep ranges.
Find a known signal source. Crystal oscillator in your computer,
27MHz CB walkie talkie etc. Use that to check the faster sweeps.

Now comes the hard part.
In a perfect world, frequency response and transient response are
equivalent. In the real world, where you're looking at tranisents,
I prefer to optimize transient response.
Stick the calibrator output into your vertical input.
(I'm assuming the scope has one. If not, skip the step.
Most generators are worse than the scope.)
If the corners are mostly square, you're done.

Don't open the case if you don't have the manual with calibration
procedures and the equipment specified. You can substitute
equipment, but your question suggests you don't have the knowledge
to do that. Virtually any <non calibration> generator you pick
will be worse than your scope. Just getting the waveform into
the scope without degrading it is an art.

RESIST TEMPTATION TO MAKE IT PERFECT.
YOU RISK MAKING IT MUCH WORSE.
RESIST TEMPTATION TO LET YOUR BUDDIES TALK YOU
INTO MAKING IT PERFECT.
IF IT AIN'T BROKE, DON'T FIX IT.
IT WILL NEVER BE PERFECT, DON'T EVEN TRY.
If it's far enough out of calibration to need significant tweeking
it's probably broke. Fix it before you try to calibrate it.
Leave the covers on and enjoy your scope.

The above assumes the scope works and nobody's been inside
messing with adjustments.

Scopes are great for looking at waveforms. If you need to
know the frequency of something, use a counter. If you need
to know the voltage of something, use a DVM.

mike
designed scope calibration generators in a former life.

 

[robb]

You need to be a lot more descriptive about what you're trying to
accomplish.
If you have other uses for the generator, use those criteria for your
decision. If ALL you want is to calibrate the scope, forget it.

I know just enough to realize that best option for calibration
is... send it to a lab.

however, i want to be able to test my scope's range of
functioning initially and (on occasion) then use the generator
to inject signals into circuits that i might be hobbying with
later (or any other usefullness)

For calibration purposes, a generator won't do you any good unless it
has the waveform precision you need and also has traceable
calibration. You can't afford that.

It's a binary situation. If you use your scope in business, and
maintain any certifications, you must send it in to have it done right.

just **hobby** use....
it would be a short lived, fault ridden business buying a abused
scopes from the bay and trying to start some electronics related
business with that equip.

these were purchased on hobby budget and will be used as hobby
tools.

i would just like the peace of mind (on hobbyist budget) that
the scope is not dead or way off on certain settings....
so , my thinking is to run scope through a range and
combination of measurements to know if it gives the expected
behavior (read, some close or near expected measurement/wave/func
form )

For hobby use, my experience says that a TEK scope either works "close
enough" or it needs fixed. A scope is a poor tool for making
measurements. It's great for "looking at the waveform", but unless
you have a scope with built-in counter and DVM, you won't get accurate
measurements.

The tek 2236 does have a built in autoranging DMM (w/frequency,
period, width, 0-2G-Ohm meas, etc ) that can be used through a
"separate" leads port or will display the measurements from
channel 1 concurrently with CRT plus more stuff

Here's how you check a scope.
If it's a CRT scope, there are some things that mess up everything.
Wrong high voltage can shrink or expand the display. A sure sign
is if the display changes size when you change intensity. Make sure
that's not a problem before you go tweeking stuff. Ditto for
other power supplies, but the effects can be much less dramatic.

my scope passes this test but i read "online researching" that
the tek 2236 has virtually NO power supply isolation and the
measurements get munged by it's own noisey power supply ???
anyone know about this

i have seen where there appears to be slight noise (small fuzzy
waves and pulsing) in the sweeps and was wondering if this was
the isolated power supply issue or another fault in the scope ?

Do all the functions work? check.
Does it trigger? check.
Use a T-connector to put your DVM and a variable power supply into the
vertical input. Compare deflection against your DVM. Check
Stick a transformer from the AC line into the input. Wall wart etc.
Does it look like 60 Hz. or 50Hz. depeding on where you live.
You can check several sweep ranges.
Find a known signal source. Crystal oscillator in your computer,
27MHz CB walkie talkie etc. Use that to check the faster sweeps.

great, thanks for that, i will try those reccomendations ....

Now comes the hard part.
In a perfect world, frequency response and transient response are
equivalent. In the real world, where you're looking at tranisents,
I prefer to optimize transient response.
Stick the calibrator output into your vertical input.
(I'm assuming the scope has one. If not, skip the step.
Most generators are worse than the scope.)
If the corners are mostly square, you're done.

the built-in scope probe calibrator is what i used for first
trace test and probe calibration ( 500 mv P-P 1 kHz )

FWIW the probe calibration gave picture perfect CRT image of over
and under shoot wave form when turning the calibration screw on
probe. that is leading edge of square wave turned up or down
while rest of wave remained flat and steady ???

when adjusted the form was square, even width and flat across the
CRT.

Don't open the case if you don't have the manual with calibration
procedures and the equipment specified.

learned that lesson a while ago

thanks mike for taking time to help an amateur hobbyist, thanks
for info and ideas

robb

 

[robb]

http://www.google.com/images?q=Fluke-5820A

How are you planning to verify that the crap you buy on ebay
is giving a valid output?
Anything without a recent NIST-traceable certificate
is only adding more variables to your situation.

If you have doubts about the accuracy of your scope,
take it to a metrology lab
for calibration with NIST-traceable standards.

Hey Jeff, can always count on you shooting straight, narrow and
succinct.

i do not need traceable calibration

as an amateur hobbyist, i just want to put the new scope through
wide range of measurements to see if there are any gross problems
.... if scope measures close on varied ranges then i have peace of
mind that scope is in fair working order.

so if i test an unknown scope with unknown signal generator and
they both come close in agreement i think i can be
**statistically** comfortable that both are in close enough for
hobby work condition.
if they do not agree well then i can use some other means to test
signal from generator then go from there.

this is part of the hobby i have 2 x 2236 for scopes from the
bay.... a scope and parts spare for under $90 (*delivered*) one
appears to be functioning well, the other maybe working well and
that suits my hobby budget

calibration is what... $150 ? thats more than the two and
shipping combined

thanks again for the response, thoughts and straight shooting
robb

 

[robb]

Hi,
You have a built-in calibrator in the 'scope. One I'd like will be
multi wave form capable with variable frequency and out put level.
If your set up means calibration, then the generator should be
calibrated against known reference as well. I send in my 'scope
to a lab to maintain it's calibration official.

yes, calibration test, but just for peace of mind and something
to test the range of the scope
i would not change anything or tweak if the scope was close,
maybe attempt a repair if grossly out of spec

calibration would likely cost much more than i paid for the
scopes including delivery.

thanks for reply ,
rob

 

[Bob Masta]

there is quite a variety of sig/func generators on the bay ...
just wondering if there is a basic series or brand to looking for
to test/setup a tek 2236 scope ?
thanks
rob

If you want to test the time base at the low end,
you can use the signal generator from my Daqarta
software with your sound card. Sound cards use
crystal time bases, so you get pretty decent accuracy.
At a sample rate of 48000 Hz the max sound card
output will be under 24000 Hz, so you won't be
able to calibrate below 50 usec per division. At the
low end there is no particular limit, since the generator
maintains the timebase accuracy for as long as you
want to wait. (Of course, you need to use a pulse or
square wave to pass the sound card's AC coupling cap.)

Daqarta also has a wide variety of available waveforms,
including different kinds of noise, plus you can provide
your own Arbitrary waveform or even play a WAV file.

Sound cards have no intrinsic amplitude calibration...
they are perfectly repeatable, you just don't know what
the attenuator steps are, or the full-scale range. Daqarta
has an Auto-Calibration feature to figure out the attenuator
steps, but you need something external to calibrate full scale.
But once you do that, you're all set. The attenuation range
is usually quite wide (more than 60 dB) and you can also
change the size of the digital waveform to take that even
farther... 90 dB is fairly easy to get.

By the way, the Daqarta signal generator is FREE.
At the end of 30 sessions or 30 days, the input capabilities
will stop (unless you purchase), but the output and analysis
capabilities keep on working. You are welcome to use it forever like
that.

Best regards,


Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Signal Generator
Science with your sound card!

 

[redbelly]

robb wrote:

{Excellent advice snipped}

Stick a transformer from the AC line into the input. Wall wart etc.
Does it look like 60 Hz. or 50Hz. depeding on where you live.
You can check several sweep ranges.

Or: holding a bare wire or unbent paper clip, touch it to the input.
Look for 50 or 60 Hz as appropriate.

Mark

 

[robb]

If you want to test the time base at the low end,
you can use the signal generator from my Daqarta
software with your sound card. Sound cards use
crystal time bases, so you get pretty decent accuracy.
At a sample rate of 48000 Hz the max sound card
output will be under 24000 Hz, so you won't be
able to calibrate below 50 usec per division.

thanks Bob, it maybe enough to give me piece of mind ?

thnaks for reply,
robb

 

[Wayne P. Muckleroy]

Krohn-Hite 1400A...very cheap good quality. does sine square triangle. It
can also sweep frequency and amplitude.

Krohn-Hite makes very good oscillators and have been in business for many
years.