AFG-2225 Function Generator Review & Testing (Ongoing)

[ACvolts]

Greets,

I bought a AFG-2225 from Instek.  Tequipment > 448.??

Now I'm testing.  And the voltage I am getting out of this kicker
is higher than it says on the screen.  It does Vpp and Vrms and
Vdbm? (forget that one, maybe it was Vdbc?).  Now I am thinking
that the higher volts is for when you have a load, it goes down
to the voltage specified on the screen of the AFG.  It's like 3 volts
higher for Vpp.  Screen I have it at 3 Vpp, then its 6.7 V on 3 different
DMMs.  One is a TRMS meter and the others or just normal.  The
normal DMMs are even a bit higher then the Trms Meter.  Since I
never had one of these Arbitrary Function Gens.  My question is:

Is it normal to have a higher voltage for loads? 

The Freq. is spot on!  Still have to test the Freq. Counter (5Hz - 150 MHz) in
the AFG-2225.  Going to do screen shots but.  I have a 7 day window to
return if it's not working right.  Your thoughts on the question and
what to look for if the little bugger is not working please.  Thanks.

I will post more testing results as I get a chance to get down and
dirty.

ACvolts

P.s. I don't like it that it doesn't do DC!  It does allow external but
it spits out at one Freq. 20kHz.   Bugger!

[ve7xen]

Signal generators are generally designed to terminate into 50 ohms by default. There is usually a setting for HiZ or something like that which will keep the 50R output impedance but adjust the output voltage assuming a high impedance load.

Either load it down with 50 ohms or set the HiZ option and you should see close to what you set.

It's not clear from your post, but remember Vpp and Vrms aren't the same thing (nor is Vp the same as Vpp).

[ACvolts]

Signal generators are generally designed to terminate into 50 ohms by default. There is usually a setting for HiZ or something like that which will keep the 50R output impedance but adjust the output voltage assuming a high impedance load.

Either load it down with 50 ohms or set the HiZ option and you should see close to what you set.

It's not clear from your post, but remember Vpp and Vrms aren't the same thing (nor is Vp the same as Vpp).

Vpp is Volt PeaktoPeak, Vp is Volt Peak(or Volt Max?), Vrms is Volt RootMeanSquare
Thanks for reminding me about the HiZ, going to do that next.

I have a True rms DMM, 2 to be exact and will use it's features.  It has PEAK feature
on it and Max/Min.  Plus I am going to test it with my Instek GDS-1072a-u scope.

Got any tips for testing?

ACvolts

[ve7xen]

Vpp is Volt PeaktoPeak, Vp is Volt Peak(or Volt Max?), Vrms is Volt RootMeanSquare

Well yer, just don't confuse them . This diagram on wiki isn't bad.

Got any tips for testing?

Turn it on, confirm the output 'looks right' and start using it! It's new and not complete junk, unless you're doing precision metrology you should be able to just trust it to do what it says. If you want to do more testing, test the things you want to test

[fpliuzzi]

Here's a handy bit of info from B&K pertaining to this situation...

"Why isn't the output voltage correct?...

Many function generators are designed with a 50 ohm output impedance. This is because the common RF connection cables (e.g., RG-58/U) have characteristic impedances of 50 ohms. Some generators have adjustable output impedance. The amplitude of these generators is correct when the generator's output is terminated in a load that matches the output impedance. Thus, if you first terminate the output with the proper feed-through terminator, you'll measure the same voltage as the generator's setting. If you operate a 50 ohm impedance generator into a high impedance input, such as an oscilloscope with a 1 Meg input impedance, you'll see approximately twice the stated generator output. A quick test is to put a non-reactive resistor (e.g., a carbon film resistor) across the output terminals of the suspected output impedance of the generator and check the voltage output across the termination resistor. Be careful not to exceed the resistor's power rating."

"There's a lot of ringing on my pulses/square waves...

You probably have an impedance mismatch. Another symptom is that the measured amplitude on the scope won't match the generator's setting (see the previous question).

When you input a signal using coaxial cable into an oscilloscope with a high input impedance, you should terminate the coaxial cable with a 50 ohm feedthrough termination at the oscilloscope's input. If you omit the termination or put it on the output of the generator, you will have an impedance mismatch at the other end of the cable (where it connects to the scope) and you will see ringing on fast rise time edges. If you don't have a 50 ohm BNC feedthrough termination, a 50 ohm carbon film resistor will work fine; don't exceed the power rating of the resistor."
-----------------------------------------------------------------------------------------------------------------------------

One of my older audio signal generators needs to have its internal 600 ohm termination switched on for its output meter to read correctly. As far as measuring the signal level of some of my sig-gens, I cannot use any of my DMMs because their AC bandwidth is pretty poor.

I keep a vintage piece of HP gear around so I have at least one meter that can measure the amplitude of high frequency signals. My HP410c has a 700MHz bandwidth (useful out to 1.2GHz according to HP). Unfortunately, I do not have a high bandwidth scope on by bench (yet).

Regards,
Frank

[ACvolts]

Vpp is Volt PeaktoPeak, Vp is Volt Peak(or Volt Max?), Vrms is Volt RootMeanSquare

Well yer, just don't confuse them . This diagram on wiki isn't bad.

Got any tips for testing?

Turn it on, confirm the output 'looks right' and start using it! It's new and not complete junk, unless you're doing precision metrology you should be able to just trust it to do what it says. If you want to do more testing, test the things you want to test

Ok, thanks for the tips.  I found something wrong with the AFG-2225.
See my next post.

ACvolts

[ACvolts]

Here's a handy bit of info from B&K pertaining to this situation...

"Why isn't the output voltage correct?...

Many function generators are designed with a 50 ? output impedance. This is because the common RF connection cables (e.g., RG-58/U) have characteristic impedances of 50 ohms. Some generators have adjustable output impedance. The amplitude of these generators is correct when the generator's output is terminated in a load that matches the output impedance. Thus, if you first terminate the output with the proper feed-through terminator, you'll measure the same voltage as the generator's setting. If you operate a 50 ? impedance generator into a high impedance input, such as an oscilloscope with a 1 M? input impedance, you'll see approximately twice the stated generator output. A quick test is to put a non-reactive resistor (e.g., a carbon film resistor) across the output terminals of the suspected output impedance of the generator and check the voltage output across the termination resistor. Be careful not to exceed the resistor's power rating."

"There's a lot of ringing on my pulses/square waves...

You probably have an impedance mismatch. Another symptom is that the measured amplitude on the scope won't match the generator's setting (see the previous question).

When you input a signal using coaxial cable into an oscilloscope with a high input impedance, you should terminate the coaxial cable with a 50 ? feedthrough termination at the oscilloscope's input. If you omit the termination or put it on the output of the generator, you will have an impedance mismatch at the other end of the cable (where it connects to the scope) and you will see ringing on fast rise time edges. If you don't have a 50 ? BNC feedthrough termination, a 50 ohm carbon film resistor will work fine; don't exceed the power rating of the resistor."
-----------------------------------------------------------------------------------------------------------------------------

One of my older audio signal generators needs to have its internal 600 ohm termination switched on for its output meter to read correctly. As far as measuring the signal level of some of my sig-gens, I cannot use any of my DMMs because their AC bandwidth is pretty poor.

I keep a vintage piece of HP gear around so I have at least one meter that can measure the amplitude of high frequency signals. My HP410c has a 700MHz bandwidth (useful out to 1.2GHz according to HP). Unfortunately, I do not have a high bandwidth scope on by bench (yet).

Regards,
Frank

Very good Frank.  I appreciate your input.  I have a High Z setting that
I used to get a proper reading.

As I tested all capabilities of the Instek AFG-2225, I eventually got to
the "ARB" (Or Arbitrary) section of the unit.  Utilizing some  of the "Built-In"
wave forms.  I found after setting 3 parameters, Start, Length and (forgot
the button name but it's the Vertical setting of the wave), then pressing
"Done" according to the User Manual, found after hitting "Output" that the
voltage & wave form failed to display on my Instek GDS-1072a-u!      
Yes I set the Scope triggering properly!  Even did an :gasp: "auto-set" on
the Oscope.  But after 2 days, no wave/volts.  On the 3ird day however,
the AFG-2225 ARB output worked for an hour.        
I shut it down, turned it on, waited 30 mins. warm-up... In the ARB section
again, set the parameters, hit the "Done" button, hit the "Output" button
but NO volts/wave on the Oscope.   

Ok, so now awaiting RMA # and return.  So this review will have to wait.
The only lack I can say so far is that the AFG-2225 has 120/M samp, 10bits
and a 4K waveform length creation.   4K!  :sniff:

It's a nice unit though, I'm happy what it does.  It has good features and
works with the Instek GDS-1072a-u scope.

I did take some Scope pics.  I will have to get the USB stick, which I forgot
and upload some results.  But I didn't do a robust review yet with the unit
because of the hiccup.  ..hey what's this!  .oO(  )  ..Situation!

ACvolts

p.s. The Instek Oscope GDS-1072a-u is made in Taiwan, but the AFG-2225
is made in China.  The scope has better Q&A.  So it's not surprising that
the AFG-2225 had Sum Ting Wong with it.

[ACvolts]

I believe we will be getting a new AFG-2225 from Instek/Tequipment!  They seem
to understand that the unit may have something jumping around which is causing
a problem in the ARB section.  So I will keep you posted of the actions of Instek.

But I do have some pics to compare the AFG-2225 and a GDS-1072A-U scope and
a Mastech 8040 Trms DMM.  (Attached photos)  2 .bmp's are from the USB stick.
Sorry no correlating photos for the USB pics.  When I do get another AFG-2225
I will put this testing on the forum much better.

ACvolts

One pic of the AFG and then a pic of what I had on the scope.  Spot on.



One pic of the AFG and 2 pics of Mastech testing output..




Only showing volts with the Mastech 8040 here:



These come from my scope USB, no correlating pics from the AFG.  But the volts and Hz
was correct..




I'm looking forward to make a new review/partial testing.  I won't be taking it a part though. 

[ACvolts]

The pics (above post) did not include the ARB (Arbitrary section of the unit because it was not
working!) functions.  This was the 2nd day of testing.  It has nice voltage output and in the
SUM section is good for Noise+Carrier waves to test devices.  As the Ad for this AFG
states, it's good for testing Transformers or Coil work for Electricians and Electronics.

Other than the stated 4K wave form output.  I find this unit decent for the price.
You can get one now @ Tequipment.net 15%-20% off the normal price! 
And you can go to TestEquipmentDepot too 15%off. AS of (7-31-2013).
The higher end Instek AFG's above the 2225 are also on sale at Tequipment!   
AFG-3051 $1453.00 (with their 5OFF bargain) from $1800.00 for Ex.  If I could
afford the AFG-3051 I would have bought it.   

BTW, this unit does come with ARB "DC" PC software built-in wave (You have to load).
I tested this and it works with the faulty unit.  Just the "Built-IN" ARB waves in the
AFG-2225 were not functioning when I hit output when testing this particular unit.

But regular non-ARB waves have the ability to create them and you can create "DC"
waves with the "OFFset" button.  Yes you have to turn down the Applified AC voltage
to a 0.7 Vrms volts setting but I tested the output in the Sine and Square functions
with 2.9 volts "DC" offset with 0.7 volts "AC"..
A 3 volt "DC"/.001 volt "AC" volts was measured in the Mastech 8040 TRMS Bench
DMM in the previous post testing this out.  (NOT pictured)

ACvolts

[ACvolts]

Ok peeps,

We need an answer by Friday with this question..

When using any Arbitrary Function Generator, does the PC Link have
to be established for the ARBITRARY section to work with the "Built-In"
wave forms?  Or should the wave forms generate output with a
PC Link?   

I want to know before I send in this unit.  It's a long time for another
unit.

I ask this because I never had a Arbitrary Generator like this and all
the other ones never had a PC Link.  Or a Arbitrary section.   All this
new tech can be an itch one can't scratch until you get off your a**.

Thanks.

ACvolts

[fpliuzzi]

"BTW, this unit does come with ARB "DC" PC software built-in wave (You have to load).
I tested this and it works with the faulty unit.  Just the "Built-IN" ARB waves in the
AFG-2225 were not functioning when I hit output when testing this particular unit."

Hello, I do not have access to an AFG-2225 myself but I did just notice on page 182 of the pdf of the user's manual that pressing the keys REM/LOCK (F5) is needed sometimes to return the function generator to LOCAL MODE after the unit has been remote controlled by the PC software that comes with the generator.

Any chance that this REM/LOCK (F5) button sequence gets the arb output going again in your particular case?

Regards,
Frank

[ACvolts]

"BTW, this unit does come with ARB "DC" PC software built-in wave (You have to load).
I tested this and it works with the faulty unit.  Just the "Built-IN" ARB waves in the
AFG-2225 were not functioning when I hit output when testing this particular unit."

Hello, I do not have access to an AFG-2225 myself but I did just notice on page 182 of the pdf of the user's manual that pressing the keys REM/LOCK (F5) is needed sometimes to return the function generator to LOCAL MODE after the unit has been remote controlled by the PC software that comes with the generator.

Any chance that this REM/LOCK (F5) button sequence gets the arb output going again in your particular case?

Regards,
Frank

Hey Frank, thanks for replying,
Ah, actually yes.  It did work last night as we tested it.
The problem we have is that the unit is supposed to work without
the PC-Link in the User Manual.  It does NOT say a PC-Link is
required to make the little bugger Output.  We change to another
channel after one channel is working and then the IC freezes
somewhere in the AFG-2225 and then there is no Output into
either channel 1 or 2!  So again we PC-Link and somehow the unit
unfreezes thinking and after the REMLOC (F5) it works for a moment.

It's not suppose to do that.    AS we read it in the User Manual.

Sum Ting Wong!  There must be Sum Ting Wong!   
Now we have to send back the unit for exchange unless other Techs
we know say otherwise because Instek doesn't know either or
"hah" they do Know but don't want to exchange, it costs money, time,
and the hassle of production rehab.  Or and if Instek will either change
the user manual or make a FAQ on their global website.  Some where
there should be a followup for future problems.  It helps Instek, and other
companies to make changes.    I don't know if this is done on purpose to
hide this from buyers.   Or is it just a few faulty chips that the
company is hush hush on? 

Is this necessary to make the unit work in ARB mode?!  Was my previous
question in another post.  And it still remains. (SIGH)

ACvolts

[ACvolts]

Good news everyone!  I found a way to bring back the AFG-2225 ARB section output!

But before I do that.  There was so much frustration at the thing that I started to think
the Chinese were out for me.   Like a conspiracy was afoot!   

My thoughts:

Foo On Yu
He Fon Ne
Wit Man Suki
Ha Wee Sow Poo
Chi La Fe Har
Wee Sly Yu Cli

Sorry about that.  But I must vent my frustrations.  I do not wish to
offend any Asians here though.  I was just thinking about the
people in China who assembled this unit.   
...Anyhow, I feel there is a Firmware
bug in the AFG-2225 and I passed this on to Instek Taiwan:

1) Hook up AFG-usb device - cable up it's ass into your usb computer jack.
2) Start your AFG software utilizing your PC interface.  Select ex. Sine wave.
3) Send it to the AFG-2225 where it's states "REMLOC" on AFG screen Press(F5). Disconnect Cable.
4) DO NOT SWITCH CHANNELS.  DO NOT DO ANYTHING BUT TURN OFF THE UNIT.
5) Turn it on and hit ARB button.  Select wave, input START>Length>Scale.
6) Press Done (F5).  Now press "Output".  Should be working again.
7) Repeat if it doesn't output volts/ARB waves at any other time.

And before you change channels, turn off the ARB section in one channel.
Then you can use the other channel.  They need to fix this bug.  But the
rest of the unit is rock solid, even the nice 5Hz-150MHz Counter!

I'll be back with more pics and tests.

ACvolts

[ACvolts]

Update on the bug in the AFG-2225!

It seems that the problem that the AFG-2225 has in the firmware is:

The menu system in the "ARB" section has 2 Outputs.  One for
"Built-In" Arbitrary wave forms and another one where you can
build one from scratch! (I'd like to scratch right now but we won't
go into that).  It seems that when I got the PC software link to
make the Output work on the unit is that the PC software took
over the Output to make it from 0-4095 or 4k points allowed.
When you send the wave form made in your PC thru the software,
it kicks up that Output to whatever you specified in the wave
you created.  The problem was when I received the unit the
Output section for the "Make your own wave from scratch"
section had the "Length" parameter set to "2".  And somehow
no matter what you do if you own this unit, go in there when
setting up, make sure you set it from 0-4095 (The Make your own
wave form from scratch "Output" section, um, I forgot the exact
menu button) and this should take care of the problem.

I informed Instek Taiwan and they are giving this info to the
Engineers.  I made sure that somehow the 2 Output sections
may have a conflict in the firmware and that this shouldn't
be happening.

I am further testing the unit now and haven't had the time
to make pics in the Instek GDS-1072a-u.  As I focus on different
items I am testing out, I will eventually get to updates here.
It will be along the lines of home made transformers right now.

Thanks Instek for your inquiry to resolve this matter.

ACvolts

[Diederik]

I've just got a brand new AFG-2225 delivered, but I'm not happy at all with the square wave output performance. If the frequency is changed using the dial, then the amplitude drops and the phase is lost. It looks like they're using the DDS from the AWG to generate the square wave, and the DDS is reset when changing the frequency. Why on earth haven't they used a VCO/NCO for this?

This is clearly visible when we hook the AFG to a oscilloscope, and the variation in amplitude appears to be tens of percents. See the attached plot. When using a sine output, everything is just fine though. I've asked GW Instek if this can be worked around somehow, but haven't received a response yet.

Diederik

[Diederik]

After an extensive e-mail conversation with GW Instek, I found out that this behavior is unfortunately by design. They amplitude drop was added on purpose to prevent any overshoot, and the loss of phase is likely just due to using (and resetting) a DDS.

Nevertheless, they have been very helpful and quick in their responses . Their support is excellent, so I'm sticking with GW Instek for now and will buy a 2125 instead, just as they advised. That one supposedly has a dedicated circuit for outputting a square wave.

Diederik