TSP #107 - Tutorial, Teardown & Experiments with Stanford Research SR530 Lock-in Amplifier

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

[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.

[videocouk]

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 YouTube. 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.

[nftmaster]

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

[maurosobreira]

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

[carlosvazquez]

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.

[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!

[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.

[schmsimo]

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

[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.

[dwagner]

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!

[jimmy_jamesjams_a_lot]

‘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!!

[techtalkmike]

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.

[petr_e]

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

[jman]

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!

[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.

[yaghiyahbrenner]

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

[patim]

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.

[rkupka]

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

[JetNmyFuture]

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