What type of funct generator do I need & why do the prices vary so DRAMATICALLY? - Page 1
Forum section: electronics / beginners

author: Bubble-Flow
author_rank: Newbie
timestamp: May 08, 2020, 11:20:10 am
content: Hello everyone,I am sorry for this silly question but I have absolutely no clue about electronis and would appreciate any help!I was assigend with the task of obtaining prices for a suitable wave or function generator and amplifier and just discovered that the prices range from just over 100 to over 3000 $.I am currently working on my PhD project which requiers using an ultrasound transducer.So far I have been operating the transducer with a borrowed function generator and amplifier from a different department. My current generator is a Agilent 33220A Function / Arbitrary Waveform Generator, 20 MHz and my amplifier works with 28V and 2.2 A.My transducer's frequency spectrum is 30-50 kHz and I have been using a Sin wave with a frequency of 38 kHz for producing a standing sound wave and obeserving cavitation bubbles.I strongly believe the generator is intended to be used for further research for projects following mine and for the next 10-20 years at least.I haven't been told anything else. So what am I supposed to be paying attention to and why do the prices vary so much if they are essentially doing the exact same thing?Thank you!

author: unitedatoms
author_rank: Frequent Contributor
timestamp: May 08, 2020, 11:32:52 am
content: One of the reasons to choose particular device how much is the integration effort. Say a software person who works a lot with Scpi based instruments will prefer device with good documentation about control language even when everything else is as good in similar but cheaper devices.

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 08, 2020, 11:39:05 am
content: For the present (sine wave ultrasound) you may be happy with any $100 generator. But who knows what you may need in the future?Generators vary with frequency range, output voltage range, output power, signal types, signal quality, external inputs (for signal modulation), external control (via PC).You may buy a cheap Chinese 6600/6800 function generator and be happy, even the next 20 years. Then with practice and experience, you will understand if you need something more powerful and expensive.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 08, 2020, 11:48:44 am
content: From your description it really sounds like you will be more than fine with the cheapest $100 instrument.Though, I think the sweet spot (money vs. features wise) now is a $250 Rigol or similar two channel arbitrary waveform generator, and it will provide quite a lot of features for the future projects. For example, at some point, you may want to drive a bridge with complementary signals, in which case two channels are useful. Features like being able to generate sweeps, bursts, modulation, etc., were considered "advanced" maybe two decades ago, but now they come in the cheap $200 Chinese models as standard, so even if you don't need them now, you'll get them for so cheap that it doesn't make much sense trying to find a more basic, old model second-hand, unless you are really constrained on money (say have only $50).You can see the $200 stuff maxes out at about 20MHz, but that's already three orders of magnitude more than you need for your ultrasonic research! More expensive products provide higher frequencies, or extremely stable frequencies, which I think you won't need.

author: AVGresponding
author_rank: Super Contributor
timestamp: May 08, 2020, 12:07:33 pm
content: It seems other people haven't bothered to read your post properly, hence the recommendations to buy a cheap product.I have no problem with cheap, but given the apparent intended use case being daily use in an academic institution by non-electronics engineers, with a service life of 1-2 decades, it is completely inappropriate here.There are primarily two reasons why some devices are cheap, while others are not.One is general build quality. Cheap ones are just that, and frequently fail right out of the box. To suggest a Feeltech could last 20 years in such a use case as yours is frankly laughable. There are several threads in this forum detailing how poor they are, and how support is pretty much absent.Which brings me to the second major difference; after-sales support. Reputable companies like Agilent, Rohde & Schwarz, Tektronix, and new-kids-on-the-block like Siglent sell a great deal of equipment to Universities, and in order to keep that business, they offer extremely good after sales support.They will frequently bend over backwards to help people like you out when there's a problem. Good luck even getting a reply from the likes of Feeltech.For a serious use case like yours, you'll save more money by buying quality gear, and therefore only having to buy it once, and not having your research interrupted by failures, or even worse, corrupted by way-off-spec outputs or other such random things that you might not notice right away.Yes, big brand gear can also have such failures, but they arefarmore uncommon.

author: ArthurDent
author_rank: Super Contributor
timestamp: May 08, 2020, 12:21:52 pm
content: My feelings are the same as above. One other thing you may want to consider is whether you'll get results that can be reproduced. If the equipment you buy is different from the equipment you have borrowed, there may be even minor differences in set-up or whatever that produce different data. Also getting very cheap equipment might mean that it will not be as reliable or last as long as better built more expensive equipment. Theoretically 'parts is parts' as they say and any source and amplifier with similar specs should work.There is a saying: "better to cry once when you buy it than cry every time you use it."

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 08, 2020, 12:23:24 pm
content: Quote from: AVGresponding on May 08, 2020, 12:07:33 pmYes, my answer was more about private DIY use type. For University institutions it is much better to buy middle-price devices ($250-$500) from one of the reputable companies. They usually offer good deals for educational projects.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 08, 2020, 12:26:18 pm
content: $200 Rigol, Siglent and similar are of completely acceptable build quality and reliability, and come with warranties.If you need a hammer, don't buy a $0.50 plastic toy hammer, but by all means buy a decent basic $10 hammer. No need to buy a $1000 golden hammer if you don't need it.

author: TimFox
author_rank: Super Contributor
timestamp: May 08, 2020, 03:40:32 pm
content: To the OP: what frequency accuracy and stability do you require for the experimental work?

author: Bubble-Flow
author_rank: Newbie
timestamp: May 08, 2020, 05:54:47 pm
content: Quote from: TimFox on May 08, 2020, 03:40:32 pmAs mentioned before, my transducer operates in the 30-50 kHz range. The acoustic field looks best with 38-40 kHz though. The important thing is that the piezoelectric crystal doesn't get damaged and the wave is stable.I want to produce a standing acoustic wave to study the interaction between micro particles (solid and gas). The acoustic field will result in bubble oscillation which I am going to record with a high speed camera. So I need a pretty stable acoustic field.

author: bob91343
author_rank: Super Contributor
timestamp: May 08, 2020, 06:45:49 pm
content: You don't need a function generator. Any sine wave generator will suffice, even old used tube gear. The venerable HP 200CD covers 5 Hz to 600 kHz for instance. Its later iterations such as the 651A (10 Hz to 10 MHz) are cheap and suitable, available easily for very little money.With minimal effort you can stay under $100. Most of my generators were free from friends. I still have several I probably will never use again.

author: Bubble-Flow
author_rank: Newbie
timestamp: May 08, 2020, 07:26:36 pm
content: Quote from: bob91343 on May 08, 2020, 06:45:49 pmThis is for research purposes for a university. The generator will have to last for a few years and will be in use for a few hours every day for many months. It needs to be a robust function generator because that's what the prof has asked for and I might have to change my transducer and go to higher frequencies and I would have to use a square function to protect the crystal instead of the sin wave i am using right now.I just want to know what kind is suitable and what specifications I should look for.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 08, 2020, 07:42:58 pm
content: Again, specification-wise, any modern FG on the market exceeds your requirements by many orders of magnitude, unless you have some non-trivial secret sauce you haven't disclosed or even hinted about, but I doubt it. (Doing ultrasonic-related things myself as of now, and my Rigol DG822 FG does more than well enough characterising my input stages.)For robustness, pick a known brand, though. If you want to be extra careful, "nobody gets fired by buyingIBMKeysight", but I really think well-known Chinese brands such as Siglent and Rigol are just fine.Well-known brands start a bit below $200, but if you want to future proof it as a general-purpose lab instrument, I suggest you go to around $250-300 so you can pick a 20MHz, dual channel model instead of, say, 10MHz single channel because the relative price difference is small and by paying some $20 extra to get a second channel, you have a very good bang-for-buck ratio.The answer to your question why the prices vary so dramatically is because the really expensive models have specifications that exceed your requirementseven morethan the cheap models. The more specialized a Test&Measurement instrument becomes, the price increase per feature increase is quadratic or exponential. This is because the lower-end models sell in larger numbers, amortizing the cost better, and also because designing instruments to a specification two times better may require ten times more time and skill. For example, you can get a proper 4-channel 100MHz oscillosscope for $400, but you certainly can't get a 4-channel 1GHz scope for $4000.

author: AndyC_772
author_rank: Super Contributor
timestamp: May 08, 2020, 09:43:36 pm
content: Regular ultrasound user here...The expensive feature in a signal generator is bandwidth, but thankfully that's not really an issue here. Any sig gen will produce ultrasonic frequencies up to a few MHz with no problem.Do look at the maximum output voltage. Ultrasonic transducers are high impedance devices, so getting any reasonable amount of power out of them (and by "reasonable" I mean "enough to detect when they're operated in ways that are interesting and informative") can require a high pk-pk voltage.Also consider the waveform shapes you can produce. Sine waves are a good start, square waves contain harmonics that could either be useful or problematic depending on your application. Other wave shapes may also offer interesting trade-offs that are fun to learn about.For that reason an arbitrary wave generator would be a very good choice, but do consider how easy it is for someone using the instrument for the first time to set up arbitrary wave shapes. (I have a Rigol DG4062 which is decent enough for the price, but the software is embarrassingly bad, so setting up arbitrary waves is just painful. There's a *lot* of room for improvement here).

author: wizard69
author_rank: Super Contributor
timestamp: May 08, 2020, 10:19:03 pm
content: Quote from: Bubble-Flow on May 08, 2020, 07:26:36 pmThe information you supplied so far indicates that any decent function generator will work. As I understand your posts you are feeding the function generator output to an amplifier. If this is correct then you only need to be concerned that the output is capable of driving that amp. So ideally you would have specs on the amp to make sure you can drive it to full capacity.The bigger question is why did the professor hand this off to you? You should check to make sure he doesn’t have needs beyond what we understand at the moment. Frankly knowing universities and the strange funding they sometimes deal with I’d want some sort of price range. He might have a budget with a lot of discretion or a grant constrained to this one instrument. In some cases it makes sense to spend all of the money available, this might include accessories and calibration contracts.There is a massive range of equipment available which might meet your needs. A high end solution like:https://www.thinksrs.com/products/ds360.htmlmight not be needed. It certainly isn’t needed for what you have revealed so far but that doesn’t mean the professor doesn’t have plans that might make use of its low distortion. Personally in situations like this it is likely best to go to Keysight, Tektronix or similar manufacture and buy a quality function generator. This guy is likely over kill:https://www.keysight.com/us/en/products/waveform-and-function-generators/33210a-waveform-and-function-generator.htmlbut is well supported.By the way somebody mentioned the importance of communications and programability. I see this as extremely important for a long term buy. The guy that follows you could easily want to setup an automated experiment. At the very minimal you want USB and Ethernet connections.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: May 08, 2020, 10:35:51 pm
content: Something not mentioned in prior posts is ability to control the unit with a computer. You will save yourself much time in experiments if you can control outputs and timestamp them to correlate with your other measurements. You really need to think through your experiment design before committing to an instrument. The capability extends down into relatively low cost instruments, but is not universal.This is a real problem that permeates industrial employment, it is not just associated with Phd theses.You need to plan the whole process, taking into account limits on timing and amount of funding, the deadline for your dissertation and the technical requirements for your experiments. Things like power output, stability, harmonic distortion and the like. You probably don't know now what is needed, and would have to run experiments (or possibly review literature) to learn. Do your bubbles form differently at 48.0023 kHz than they do at 48.018 khz? What is the relation between the waveform you use to drive the transducer with the pressure field at the bubble location region? Do you care about any of that? You may need to over specify to give you the ability to answer those questions (and include in your thesis).You should consider your borrowed equipment as the tool that lets you learn enough to make those plans.

author: rsjsouza
author_rank: Super Contributor
timestamp: May 08, 2020, 11:03:23 pm
content: I echo the suggestions of folks here regarding purchasing a decent waveform/signal generator and I think the peace of mind, reliability, warranty, good software and user interface are the key factors, as technically your application is very well covered.In order of nice interface and usability in general, I usually put the Rigol DS4062 as the top - it has an oscilloscope-like interface and very large screen, which helps. Second I put the Tektronix AFG1022 which, despite being a bit more expensive and go to a lower frequency than the Rigol, it has the more traditional smaller form factor and a very nice panel and buttons. The Keysight model you currently use has a very small screen for my taste and therefore ranks lower in my opinion. All three brands have solid track record for reliability and quality, but the Rigol's control software (if you care for it) is not great. I like Keysight's but it costs extra. I never used Tek's.I don't know the other models mentioned, but I know Siglent and Rigol came with more recent offers that pack more punch in a smaller package and price.If possible, I would estimate a budget between $500 and $1000 if you intend to go for the A brands. Who knows? Maybe the university may get discounts on certain brands.Anecdtoctally, my university used several aforementioned ancient audio and function generators from HP and they were workhorses. However, the university didn't have much money and we had to deal with what we had.Good luck in your search.

author: Bubble-Flow
author_rank: Newbie
timestamp: May 12, 2020, 12:06:13 pm
content: Thank you everyone. I looked through a lot of offers and considering everything, especially the harmonic distortion in the frequency intervall I am going to work in and the high sample rate for a smooth sine wave, I think the Keysight 33500B would be suitable.I also talked to the electrical engineer of our department, and he advised me to get an arbitrary waveform generator with Ethernet port. What is so special about having LAN? He said USB wasn't very important. Unfortunately I didn't ask him when he mentioned it.Another thing he mentioned was floating output. What advantages does not having a floating output provide?

author: wizard69
author_rank: Super Contributor
timestamp: May 12, 2020, 12:58:47 pm
content: Quote from: Bubble-Flow on May 12, 2020, 12:06:13 pmIt should do. However since you are primarily working with Sine waves I'd make sure using them and adjusting the frequency is as easy as you need.QuoteSo that you can network the instrument. That probably sounds obvious but it is fairly common to automate test and measurement especially for experiments that may need to run for a long time. There might not be much data collection to come from a signal generator but there may be good reason to send parameters to the unit over time. A LAN connection just makes communicating with the device easy and simplifies things when you have a larger number of instruments working together.Consider why networking computers is so common these days. A local network allows for all sorts of possibilities between machines. Then you go to wider world and you haven another set of possibilities. In the same way you have multiple possibilities hen connected via a LAN. For example one can send and receive instrument setup data, trigger devices, capture data & etc.QuoteI would disagree. However that depends upon what capabilities the instrument provides over USB. For example a waveform generator might allow you to load waveform data from USB. Now you should be able to do this over the LAN too but taking the time to do setup the LAN might not be worth it.QuoteYou will have to ask him what he was thinking. I would think that floating outputs are desirable to avoid ground referenced signal lines. I suspect communications issues here.

author: rstofer
author_rank: Super Contributor
timestamp: May 12, 2020, 01:38:48 pm
content: And now you know why prices vary...Your bubbles experiment can probably get by with just about anything. Lab automation is another level altogether.If I were considering any kind of experiment automation, I would want to see if I could do it with MATLAB (or LABVIEW, but I have MATLAB).https://www.mathworks.com/products/instrument/supported/arbitrary-waveform-generator.htmlIt might turn out that it's easier to write some C (or Python) code to do the automation and leave the results (if any) in a file for later processing.All of which seems like overkill for driving an ultrasonic transducer...

author: rsjsouza
author_rank: Super Contributor
timestamp: May 12, 2020, 01:44:50 pm
content: Just adding to the good points raised by wizard69.I think the 33512B is the one to get - having two channels, it allows you to not have a shortcoming after the purchase in case you need to control two systems in quadrature phase, for example. It also has the arbitrary waveform generator.According to theirdatasheet, these generators come with both LAN and USB built-in, so no need to worry regarding your options. I agree with wizard69 and personally think USB is very important as computers are quite portable and a quick USB connect can overcome a corner of the lab (or other places) that does not have wired ethernet. They also have the USB pendrive, which also helps exporting data from the generator to a regular computer in case no mobility is available (I have one of their power supplies that has all these connectivity options and it really helps with this).Floating outputs on a function generator are a good thing, but not a deal breaker. This model's datasheet mentions the outputs are independent and can be coupled, which hints that they are fully floating.

author: nfmax
author_rank: Super Contributor
timestamp: May 12, 2020, 02:04:53 pm
content: The 335xxB series are very capable function generators: I have the 33522B. The outputs are indeed floating, i.e. not internally connected to mains earth. This is useful to avoid introducing ground loops when interfacing with other equipment with 'ground' terminals connected to mains earth, e.g. amplifiers. They can generate exceptionally clean, low distortion sine waves as well as arbitrary functions, if you purchase that option. (Most options, apart from the second output channel, can be retrofitted)They have a bight, clear display, and the user interface is quite well thought out. The only thing I regularly have trouble with is remembering how to link & unlink the two channels (e.g. when I want differential outputs carrying the same signal). If you have the arbitrary waveform option, you can load a waveform from an ordinary .CSV file on a USB drive easily from the front panel, no programming required. However they are fully remotely programmable if needed.

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 12, 2020, 05:51:02 pm
content: I was curious and find that "like new" 33522B costs $2,995.00

author: nfmax
author_rank: Super Contributor
timestamp: May 12, 2020, 06:01:19 pm
content: I paid about €1600 for mine, a couple of years ago

author: wizard69
author_rank: Super Contributor
timestamp: May 12, 2020, 07:51:02 pm
content: I was actually surprised to hear that the departments electrical engineer didn't think much of USB. I suspect he is use working in a well equipped lab. The minute you need to roll a bit of gear out to a tool on a production floor, USB can be a life saver as it can simplify modest test setups. It is not uncommon for expensive instruments to leave nice well equipped labs. Our metrology department has to do validation work on sterilizers on a regular basis and has such a cart in almost permanent use. So yeah I'm not sure why USB was poo pooed here, if anything USB has become more important in the instrumentation world now that it is a far better performer.Quote from: rsjsouza on May 12, 2020, 01:44:50 pm