rcommins2 - 2014-03-07
Would you like to have femtoamp measurement capabilities on your desktop? You could for a lot less money than a Keithley electrometer.
Did you ever decide to sell these? I'd be interesting in trying one out in my lab.
+Scott Gulas Unfortunately, I'm waiting for a greater interest to develop and a better economy. I don't want to invest 10's of thousands of dollars to just sell a few. I would be interested to demonstrate my electrometer in your lab. Where is your lab? What is your application that needs an electrometer? What will you use as a current source and how do you plan to connect to it? You can email me at: richcommins@q.com to discuss this further.
+Scott Gulas Are you Scott Gulas the Validation Manager at Texas Instruments in Sahuarita, Arizona?
I got the pleasure of spending some time with Richard looking at (and actually measuring) his electrometer solution. Lots of clever techniques and a lot of great lab war stories from a rich career in the field of chromatography. The accuracy of his solution is superb (tested with a calibrated Keithley 263 SMU) with reasonable settling times. A lot of great work has gone into making his square root electrometer solution as good as it is. A very nice guy to boot!
Until now, you didn't disclosed any information about how can a device like this can be built. We can only see the ADC you've used. Nor do you sell units. At least you could teach us how to build the low cost, ultra-low noise cables, and what connectors to use. Thank you!
You know the ADC that I used? How did you figure that out? Even if you know the ADC part number, that would not tell you how I can put an ADC running at 10 MHz and 3 switching power supplies running at 100 MHz next to my electrometer on the board and still get the 1 uv low noise on the 24 bit ADC and the shot noise limited electrometer performance.
You mean that I don't sell units YET! LOL Maybe you don't understand what you are looking at here. One of the commenters here just wanted a demonstration of my electrometer. He flew out from Arizona with a calibrated Keithley 263 current source to see if my electrometer really did as I claim. He was at my home for 3 - 8 hour days to learn some of my secrets of this design. I also told him that I don't work for nothing and charged him $200/hour just to talk to me. I did not tell him all the secrets of my design either and he did sign a non-disclosure agreement too. He was amazed at what he saw.
Yes, you can go buy a 3 foot Keithley low noise cable for around $1,000 and they won't tell you either how they made it. My cable goes for around $1.00 a foot with two $3.00 connectors on it. My costs would be around $10 for the cable. With a break through like this you just want me to tell you the secrets of how to make the cable? LOL I will tell you to go get the "Low Level Measurements Handbook - 7th Edition" and read it cover to cover and if you understand it all, you will have some of the secrets you will need to get someone to build that cable for you to your specifications. They of course will have a minimum run of between 5,000 to 10,000 feet to make your low noise cable. You don't think that the cable came from Digikey or Newark do you? It is a custom cable design made especially to my design requirements. https://www.tek.com/document/handbook/low-level-measurements-handbook
@Richard Commins First of all, don't get my comment wrong. I want to thank you for showing that it is possible to build such a exceptional device with low budget.
Also, tank you for the recommended book.
The ADC that I think you've used, is seen in the right lower corner of your pc software.
If i would have the possibility to sign the confidentiality agreement with you, so you can teach me,
even if I will need to guarantee with my life that I don't disclose anything, I will not hesitate!
Unfortunately, that is not possible.
I respect your work!
My email is nbogdan.contact at gmail.com.
Yes, you are correct (you have a good eye) that the ADC that I used is a older model Analog Devices AD7712. I would love to find a cheaper 24 bit ADC that works as well. There are many tricks to get the performance out of that device or any device that delivers 1uv of noise peak to peak and a full scale range of +10V using all the different supplies that it uses that is generated from the noisy USB +5V from the computer. If the supply power up sequence is not controlled, the part will latch up and burn. The ADC is just for the demo board that I designed. Any 5 1/2 digital meter like the HP34401 will do the same job of digitizing the analog output of the electrometer. Some of the magic used in the design is in the software too that I wrote in Visual Basic 6. Even if I gave you the schematic and the parts list, if you put it together, it probably still would not work for you. There are many secrets that I have discovered like the PCB design, the low noise cable and the cleaning procedure. Remember this runs from the USB port of the computer and the grounds loops need to be controlled also. Thank you for being gracious and respecting my work. If you email me at richcommins@q.com we can talk more.
Great work.
I am a beginner Electronics guy, I don't even have a oscilloscope yet. I feel like it's holding me back on furthering my learning.
But I got to say this looks like a beautiful thing you have worked hard at!
Could you recommend a halfway decent beginners oscilloscope to me?
It will all depend on what you want to do with it and how much you want to spend. As a beginner, doing beginner electronics, any oscilloscope will do. You can get many of them on Ebay for very little money like $100. As your needs increase with time, then speed and features makes the cost of the oscilloscope go up. I would get a old working (guaranteed) Tektronix scope on Ebay. I would stay away from the digital scopes for now. They all have their problems and are expensive. I would look for something like a Tektronix 100MHz scope on Ebay.
@Richard Commins okay thank you!
That makes a lot of sense the way you word it " as your needs increase, upgrade!'
I just placed a bid on one that fits your description. :-)
@Richard Commins I want to thank you for your recommendation!
I got a good deal on a tektronix 2247A for $150.00 from a Electronics recycle place. They gave me a guarantee that it works! After looking at other prices on eBay for the same thing, I feel like I got a pretty good deal? ( I don't think they realize what they had) thanks again for your recommendation! :-)
I am glad you got a good deal. I hope you get many years of use from that scope. Now you can spend the next 20 years learning how to fully use it and find all of its limitations. Read all of its manuals, both user and service manuals, check the calibration of the instrument and don't forget the manual for the 100 MHz probes that you will be using. If you bought a 1x/10x probe, learn the difference for the two settings. They need response calibration too on each input you use them on.
@Richard Commins okay thank you, sounds good! Yes I had purchased 2 1X-10X 100 MHz probes. I will read the manuals about them also, To my understanding the 10 times is a 10 mega Ohm resistor built in so, we can measure the high voltage safely. I'm sure there's more to it than that. I will read up on termination. I'm looking forward to the learning experience , calibration and everything that's involved !Thank you for everything!
here is another potentiostat (Electrometer) with about 5fA p-p noise: https://www.youtube.com/watch?v=Zjhv3lrZ0EI
Hi... I would like to know more about your solution, can you give your e-mail?
+Fernando Henrique Cardoso What would you like to know about my solution? Would you post your email here? If you do, I will email you and answer your questions if I can.
@Richard Commins my e-mail is: fernando.cardoso@lnls.br
interesting...
Is there USB isolation? Also, do you have plans to sell units? I would like to buy even if still at prototype stage.
This electrometer is still in the development stage and I didn't include USB isolation yet. I added circuitry to minimize the noise from my desktop computer, but the noise from my laptop charging supply adds noise. My intent is to add transformer isolation in the future. I'm on my 8th prototype and I have only 2 of them. Building prototypes in small quantities is expensive, so I am trying to gage the market to see how many people are interested. What is your intended purpose for this electrometer and I will let you know if it will work for you. Remember that the connection to your source current can add lots of noise unless you use my ultra low noise cable that has BNC connectors. This design is a ground based design and is not meant to float at high voltage. The low noise cable is a custom design and I have limited stock. I will have to make a large investment in procuring the cable if I go into production. I will be making a new video that demonstrates how my electrometer can measure high meg-ohm resistors easily.
Yes I have now added USB isolation from the computer. I did this by buying a "USB to USB Isolator" from Amazon.com for $40.00. When I initially installed the device my noise went up dramatically. I had to make circuit modifications to the electrometer to make it compatible with the USB isolator. Now my noise is back down to the shot noise limit at the measured current and calculated bandwidth. My electrometer no longer sees the noise from the power supply for my laptop like I described in the above comment or from my desktop computer.
I WANT TO COUNT ELECTRONS
Well this is not the way to do it. I can measure around one fA (femtoamps) which is around 6,000 electrons per second. You will need another way to count electrons.
@Richard Commins ok
Joy Miller - 2021-06-23
Your great work has resulted in tangible, beneficial results, keep it up. God bless you