TSP

In this episode Shahriar goes over the operation and principle theory behind Lock-in Amplifiers. The SRS SR530 is one of the most iconic lock-in amplifiers ever made and since it offers two channels it can be used to perform very interesting experiments across many domains. After reviewing the block diagram and equations governing the theory of operation, a brief instrument teardown is presented.
Two unique and interesting experiments are also presented. In the first experiment the instrument is used to measure the speed of light. This is accomplished by measuring the wavelength of sound at 20kHz using a pair of speakers and a function generator. The distance between the speakers can be carefully adjusted and the relative signal strength from each lock-in channel is measured and thus the wavelength can also be measured.
In the second experiment the sensitivity of a red LED to blue laser light is measured. Due to the semiconductor composition of the red LED as well as its red plastic casing, the responsibility of the LED to blue light is extremely low. A chopper is therefore used to lock the light to the lock-in amplifier's reference input. The measured induced current is measured down to very low optical level in the order of hundreds of fempto (10^-15)
The Signal Path
www.TheSignalPath.com
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www.Patreon.com/TheSignalPath

[@Thesignalpath]

Two minor corrections: I mistakenly read the symbol φ (Phi) as α (Alpha). Also, the exponent value 10^-15 is femto, I accidentally said atto which is 10^-18.

[@AdityaMehendale]

Hi TSPB - You mention around the 42:00 mark that the TIA is 10 MOhm - i.e. transimpedance of 10^7. However you say & use 10^6 in the rest of the segment. Cool explanation though :) Cheers!

[@jafinch78]

I've read you're better off with a Princeton Applied Research PAR-124/126. Stanford? Makes me think of billions in frauds and gross cheats as liberal as around that area can make.

[@AdrianRumpold]

And "noises of source" around 3:40 ;) Thanks for the great video and your amazing skill of explaining these highly technical topics!

[@TheCondoInRedondo]

Glad you caught this. I was just now about to post that (if you were small enough) you could conceivably COUNT THE ELECTRONS if you were truly measuring attoamps. ;) I'm guessing that lock-in amps are used to pull the feeble Voyager signals out of the cosmic background.

[@nftmaster2050]

"And here I'm using centimeters, because I'm not insane" :D

[@trickyrat483]

Clearly Mr Trump needs to build a wall around this commie's house. :)

[@JackZimmermann]

Epic! Haha!

[@hpux735]

Jinx! Lol, how many people commented that!!

[@SidneyCritic]

What's wrong with using cubic furlongs per fortnight. lol

[@RFlynn-rs6yw]

I like to use chain, link, or rod (pole) just to confuse people.

[@maurosobreira8695]

And once again you crossed that thin line between awesome electronics and experimental physics - Love it!

[@schmsimo]

Nothing better than a lazy Sunday afternoon with a new episode of the SignalPath 🍿

[@rkupka]

"...I'm using centimeters, because I'm not insane." Very nice :)

[@davidgustafik7968]

I was going to post this exact comment.

[@DanielRowe]

made me laugh

[@shazam6274]

Jimmy Carter single handedly stopped the USA from changing to the metric system. he was also the only president who was an engineer.

[@ahmedgaafar5369]

he is absolutely correct.

[@AndySpicer]

I’m here watching this a second time because of your latest video. I’m always amazed at how much I learn when I do that. My core knowledge has improved so much over the years from watching your stuff that I now have a much better grasp as I listen to new things. I’m in my 50’s and hadn’t taken a math class since I was 20. It frustrated me that I wasn’t able to remember enough to keep up with you during the videos. I went back to school specifically because of you and I’m now 2 years and 5 math classes in. Thank you!

[@Thesignalpath]

Happy to hear it! I hope you would find the videos continuously useful.

[@yaghiyahbrenner8902]

Stanford Research. what a bum response! thanks for this video.

[@3ffrige]

Right? Because they think their the market leaders for Lock In Amplifiers, they are up there on their high horse acting all mighty and shït. Reminds me of IBM back in the days and look at what happened.

[@petr_e]

That wonderful video combines signal processing, electronics and physics together! That was an introduction of lock-in amplifiers to me. Thank you!

[@dwagner6]

I’m in school for EE and am working my way through your videos. Even if I don’t understand many topics you discuss, I’m constantly researching new things and just hoping I absorb the rest through osmosis. Thank you!

[@cncdavenz]

Hi, I have pulled apart many industrial instruments over the years to see how they worked. Some had choppers and now I know what it was for. Thanks for the very concise explanation. Cheers Dave.

[@topherteardowns4679]

"Using centimeters, because im not insane' lol, love it.

[@carlosvazquez4401]

Thank you, Shariar. Amazing explanations. Maybe it is worth to mention that in this lock-in amplifier very often the input FETs are damaged, when the signal is overload.

[@bloodyl_uk]

Amazing job dude, totally in awe of the sheer amount of modern science and communication techniques you've hidden inside what appears to be a fun way to test gear and measure the speed of sound.

[@JetNmyFuture]

Breaking down the math and block diagram was awesome! Loved this one.

[@omgkingdano]

I look forward to these videos. You do a wonderful job as an educator. Keep it up!

[@Bmcarroll1]

I learn a lot from the tutorials. Thanks again!

[@The_Paya]

These might be in (my) top 3 experiments you've performed with high end specialized instruments. Immense bummer that SR couldn't lend you their latest machinery to run them on. Still awesome and enlightening. Thank you.

[@kissingfrogs]

That was awesome. An experiment demonstrating how to extract signal from within the noise and measure the speed of sound was enlightening. Thankyou Shahriar.

[@stefanosmakris5641]

Another great video. Amazing information. Thank you!

[@techtalkmike4968]

Outstanding tutorial video! The amount of time and effort and knowledge sharing is exemplary! As a TSP Patreon supporter, the ratio of bang to buck is enormous.

[@magnusarvidsson4447]

Excellent tutorial. Best I have seen on lockin amplifiers. Love your channel.

[@robertw1871]

Very nice, more techniques presented than are immediately apparent, I’m sure a lot of careful thought went into this, and to make the setup appear rather simple is brilliant, thank you.

[@gerryjamesedwards1227]

"I'm using centimeters, because I'm not insane." LOL

[@agstechnicalsupport]

Great video on lock-in amplifier operation and basic theory, along with beautiful experiments demonstrating its usefulness.

[@jman51]

We had exactly the same experience -- I too worked in an ultra-fast optics lab in undergrad, and these were truly "black boxes" to me until I found out how they worked many years later. Thanks for the video!

[@kungfumaster8171]

As usual top rate content and commentary. Excellent work. Thank you.

[@ocean6132]

This is greatest video. I like the tutorial and the two experiments designed very much. Very elegant!

[@guillemoli]

Interesting experiment setup and clear and concise explanation, as usual. Excellent work!

[@matthewvenn]

thanks for the video - very interesting. Never even heard of this instrument before.

[@simonfitch1120]

Your videos are always interesting, but this one was astonishing to me. Such a simple math principle leads to a device which can do the seemingly impossible. Thank you so much for this one.

[@gordonwedman3179]

Great video as always. Equal I'm sure to a one hour lab presentation at MIT. Thanks for all the work put into these.

[@arijitsharma123]

Superb demonstration!! I really enjoyed the video!! I hope you keep making such videos for enhancing our understanding!!

[@pa4tim]

Very nice experiments. I am building a few opacity meters and was testing some photocells a few days ago . (like measuring the sun-nano dark current). I do not have a locking amplifier and I had a hard-time measuring steady under 10nA (the meters I used have pA resolution) so I am really impressed by the measurements you showed and the very clear explanation, Thank you.

[@baghdadiabdellatif1581]

Great work 👌 Thank you Greetings from north Africa (Algerian dezert)

[@daviddoudouable]

Such a good video ! Well done and thanks a lot !

[@lazyman114]

I've watched about 50 of your videos so far and this might be my favorite.

[@theLaven]

Thank you sir. Very intuitive experiment. Please keep it up!

[@hpux735]

"And here I'm using centimeters, because I'm not insane" 😂

[@jimmy_jamesjams_a_lot4171]

‘Measure the speed of sound’. That is precisely what this device was exactly invented for. I’m quite positive it was at Princeton, hence the reason why the big competitor to the Stanford is the PARC, where it was invented I think. Great stuff, thanks for giving me a use for my Kiethley programmable current source!! Maybe I can justify keeping it now!!

[@hoaianhho33]

I love your ruler. That's awesome. BTW, thank you for your video. That made me understand about lock-in amplifier.

[@richardshagam8608]

I wish that I had seen this video years ago. Well done!!!

[@Darieee]

This video was amazing : thanks !!

[@kieranj67]

Excellent as always, thank you!

[@stanislavsubrt886]

Maan this is pure gold. Thank you for this video! Great work as always!

[@catt87]

Thank you for this video. It just made my sunday :D

[@AF6LJSue]

Thank you this was really good, I learned something. :)

[@paulfletcher848]

Truly awesome, thank you.

[@adrianramosbardin7609]

'Here Iam using centimeters, because Iam not insane' Nice touch

[@williamlee9340]

Very clear LIA application.

[@coolnj1]

Excellent tutorial. Your teaching skill is awesome.

[@MertOzdag]

Great video, thanks for doing this

[@stonail665]

Very Interesting ,Thanks for quality upload. Dorood.

[@isacnordin8048]

Amazing demonstration, easy to follow and understand

[@bobfuller]

Wow! I just watched the speed of sound being measured. How awesome is that?!

[@bfx8185]

Thx one of the best videos you did. Excellent !!!

[@Sixta16]

Hello BFX! I worked with a two Stanford SR830 back then in my first job, in an optical measurement setup. Good to remind myself how these instruments have worked! Also as a sidenote: Two lockins can be used together to make an impedance analyzer ;)

[@amciaapple1654]

I'd like to see how the Lock-In amplifier is used as an impedance analyzer.

[@Banks231]

Hi The Signal Path, Nice to meet you in ISSCC

[@Thesignalpath]

Thanks! You too.

[@video99couk]

1:15 Exactly the same response I had when I contacted a company about demonstrating a product they made which has not been covered on KZbin. They said that they are the top result for anyone searching for that product already and no they didn't one to lend me one to feature. You do have to wonder what the marketing people are on, when they get a chance to have someone in that field, demonstrate their product, but they turn it down. Like you, I demonstrated one of their products and explained why I couldn't show any others.

[@varjagg]

This is completely mind-blowing.

[@gacherumburu9958]

👍👍 22:11 "am using centimeters bcoz am not insane"..😂

[@guillep2k]

Very accessibly explanation for a very complicated subject!!! I don't have a degree but I was able to understand everything. Thank you!!

[@Starlite4321]

Incredible. Just incredible...

[@wumichael487]

Awesome tutorial thank you

[@gauravpalsingh3505]

Great work

[@AlexeiPolkhanov]

Awesome video! Thank you. I was thinking to use similar setup to measure air humidity more accurately (speed of sound depends on humidity, pressure and temp) but could not find affordable lock-in amplifier on Ebay and was scared to spend money on old one wondering if it is still works.

[@ahmedhass146]

Woow that is a great demonstration and a nice explanation thank u very much

[@Thesignalpath]

You are welcome!

[@JustSomeGuy1967]

Mind Blown !

[@benrd9111]

Very nice experiments 👍

[@MrManlop]

Thanks a lot¡ Wouldn't expect to find such a helpfull video by typing "standford sr530 lock in" in youtube

[@urizung5728]

Thank you!

[@plemli]

Can't all this be done digitally after digitising the input ? It's almost an SDR... Very good video, clear and interesting, teaching something that's not widely known.

[@AngDavies]

Nah, you'd need too much dynamic range/memory to get that kinda resolution, needing to capture the noise at the same time would put a hard limit on how low of a signal you can resolve

[@naohwatson854]

love it.

[@xDevscom_EE]

@18:35 I feel like a cat chasing the laser pointer. Not sure how's that idea works. Thanks, another video that have experiment setup more interesting than the instrument itself ;).

[@samw3086]

One of the Achilles heel of this unit is the vertical daughter card that you pointed out. It is flimsily held in place and is easily affected by any pressure on the top of the unit which rests on the top edge of the card. If there is an intermittent connection at the bottom connectors you can lose the phase output and the unlock light comes on even though you get the correct frequency on the display. Except for this, it's a fine unit.

[@ilyagulko95]

Great video! I have a follow up question to understand the LIA better - the signal that we are after, does it have to be a lower frequency signal, or can it have high frequency components?

[@amintorabi3413]

Excellent video. Ended up watching the entire thing even though I have a lab report due! Out of curiosity, what is the power spec of the front amplifiers of the lock in amp? I would imagine if you want to amplify such small signals without too much noise, you would need to burn a ton of power.

[@iNDREI_Ro]

My mind is blown. Thanks.

[@georgemihai9612]

Thank you for this video! I apologize if I repeat the comment, I thought I'd posted it already but do you have any videos where you cover the time-constant and RollOff and their implications?

[@forgetful2012]

Thank you so much for your video. It is the first time I’ve come across "The Signal Path" video and I really enjoyed it. It was very well thought out. I have done some video editing in the past so I appreciate how much work goes into making and editing such videos. I have the exact same lock-in amplifier that you used. I am new to lock-in amplifiers so I’ve decided to start with something very basic. I use a function generator to create a signal, and connect it to both the reference input and the A input. I would expect the phase to be the same as my input signal when I set the output to R and Theta. This is not the case. Would you know why? Also would you know what I should expect in this case for the different output options? Thank you so very much!

Very nice video! I noticed at 35:49, when you turn off the light, the sign of the current changes to negative. Perhaps this is some thermo-current from the connectors or some sort of electrochemical cell?

[@VinayakaHDamle]

Hey! Is there some consideration on types of cables we use.?

[@jfcrow1]

Thought provoking diode example

[@stephenstudley185]

Shahriar , I am curious as to what real-world practical application a lock-in amplifier might have? I’m also curious what level of miniaturization might be applied to the design? Could it be made as a field instrument, say for audio tracking, amplifying & recording? As always, your videos are nothing short of exceptional! I appreciate your dedication to learning for all classes. Education is the tide that raises all boats! Kind regards!

[@cowshittt]

I just realized that the lock in amp is performing hardware Fourier Transform. Consider my mind blown.

[@motherjoon]

Amazinggg

[@techsinc]

The best way to think of this is to think of it as an AC amplifier with a frequency selection bandwidth determined by the fidelity of the driving AC reference signal (within limits of the electronics, of course).

[@ruzmetovkhujabek]

thanks a lot

[@octavmandru9219]

Cool, now let's hear the butterfly flapping his wings in Brazil - from Texas :)

[@doctorzizo2008]

I like it.. i am wondering if you can also use the lock in to measure the optical phase delay?

[@spencercheung7154]

Thank you.

[@bobbybiggs4348]

How do you account for magnetic coupling between the speaker's voice coils?

[@IxIVVI]

Great!

[@KrissyD-px9gj]

I finally understand the math Just clicked Very smart whoever first came up with lockin amplification

[@rasherbilbo452]

What? No experiment using it as a ludicrously expensive AM radio? :-) Enjoyed the vid. as always!

[@raulalejandrofajardomunoz5074]

It´s a grat video, but i have a question, for example when i have a photo-electrochemical system, i have a base current caused by the raction, and also de photocurrent with the frecuency of the chopper, the first one is considered as noise? and we only gets the photocurrent of the given frecuency Thanks for the information

[@matthewgrimsley4506]

Great job. For some time, when my professor referred to these I thought that "lock-in" was a person's name.

[@ResearchAdvantage]

What about modulation of the light by driving the laser diode with a square-wave from a signal generator? How does that compare with the chopper?

[@PelDaddy]

"Magic turns into knowledge." Are you related to Doug Henning? Seriously, though, good video. Very interesting indeed. Thanks for sharing.

[@georgethomas9436]

Okay. Where can i get that ruler? I know many want to know. Great video.

[@moshet842]

Considering the sensitivity required when making this kind of measurement, does that mean sometimes they have to design their own components in these devices like this lock-in amplifier?

[@ninsimathew4341]

Hi. What are the different connectors you have used?

[@ninsimathew4341]

Hi, would anyone be able to help me understand the kind of probes and connectors that are used?