Forums

Trimpot with decent rotational life?

Started by Phil Hobbs May 9, 2017
Hi, all,

I'm doing a lab special for some folks in the physics department of the 
University of Oxford.  It's an interesting wrinkle on the laser noise 
canceller, which is going to work with some HgCdTe photodiodes at 5 
microns. (*)

These gizmos are probably significantly less linear than silicon diodes, 
so I'm giving them an offset current adjust pot so that they can tweak 
the cancellation point a little bit.  Thus they're going to be adjusting 
that pot quite often.

Trouble is, all the trim pots I can find are ~200 cycles rated 
rotational life, or not rated at all.

Any fave longer-life trim pots?

Thanks

Phil Hobbs

(*) I'm getting a factor of nearly 10 improvement in cancellation 
bandwidth (in the spherical-cow SPICE universe) by putting a bandaid on 
the MAT14 supermatch quad NPN.  It uses one SiGe:C NPN to make a 
Darlington, thereby returning nearly all the base current to the 
collector, and another one as a CE stage looking at the MAT14's base and 
driving the other SiGe's base to force the MAT14's base to stay still 
out to high frequency.   I have to put in bias at the MAT14 base and 
take it out again from the collectors, but since I need an offset 
current pot anyway that's not much of a worry.

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
Den tirsdag den 9. maj 2017 kl. 23.17.57 UTC+2 skrev Phil Hobbs:
> Hi, all, > > I'm doing a lab special for some folks in the physics department of the > University of Oxford. It's an interesting wrinkle on the laser noise > canceller, which is going to work with some HgCdTe photodiodes at 5 > microns. (*) > > These gizmos are probably significantly less linear than silicon diodes, > so I'm giving them an offset current adjust pot so that they can tweak > the cancellation point a little bit. Thus they're going to be adjusting > that pot quite often. > > Trouble is, all the trim pots I can find are ~200 cycles rated > rotational life, or not rated at all. > > Any fave longer-life trim pots? >
can't use a regular pot? https://www.digikey.com/product-detail/en/bourns-inc/3310Y-001-103L/3310Y-001-103L-ND/1088215
On Tuesday, May 9, 2017 at 5:17:57 PM UTC-4, Phil Hobbs wrote:
> Hi, all, > > I'm doing a lab special for some folks in the physics department of the > University of Oxford. It's an interesting wrinkle on the laser noise > canceller, which is going to work with some HgCdTe photodiodes at 5 > microns. (*) > > These gizmos are probably significantly less linear than silicon diodes, > so I'm giving them an offset current adjust pot so that they can tweak > the cancellation point a little bit. Thus they're going to be adjusting > that pot quite often. > > Trouble is, all the trim pots I can find are ~200 cycles rated > rotational life, or not rated at all. > > Any fave longer-life trim pots? > > Thanks > > Phil Hobbs > > (*) I'm getting a factor of nearly 10 improvement in cancellation > bandwidth (in the spherical-cow SPICE universe) by putting a bandaid on > the MAT14 supermatch quad NPN. It uses one SiGe:C NPN to make a > Darlington, thereby returning nearly all the base current to the > collector, and another one as a CE stage looking at the MAT14's base and > driving the other SiGe's base to force the MAT14's base to stay still > out to high frequency. I have to put in bias at the MAT14 base and > take it out again from the collectors, but since I need an offset > current pot anyway that's not much of a worry. > > -- > Dr Philip C D Hobbs > Principal Consultant > ElectroOptical Innovations LLC > Optics, Electro-optics, Photonics, Analog Electronics > > 160 North State Road #203 > Briarcliff Manor NY 10510 > > hobbs at electrooptical dot net > http://electrooptical.net
I think long life and trim pot, don't belong in a sentence together. I'll second Lasse and suggest a regular pot. We use a lot of clarostat 392 series, https://www.digikey.com/products/en?keywords=392JA103-ND If it's a one/ few of, the price can't matter. George H.
On Tue, 09 May 2017 14:36:51 -0700, Lasse Langwadt Christensen wrote:

> Den tirsdag den 9. maj 2017 kl. 23.17.57 UTC+2 skrev Phil Hobbs: >> Hi, all, >> >> I'm doing a lab special for some folks in the physics department of the >> University of Oxford. It's an interesting wrinkle on the laser noise >> canceller, which is going to work with some HgCdTe photodiodes at 5 >> microns. (*) >> >> These gizmos are probably significantly less linear than silicon >> diodes, >> so I'm giving them an offset current adjust pot so that they can tweak >> the cancellation point a little bit. Thus they're going to be >> adjusting that pot quite often. >> >> Trouble is, all the trim pots I can find are ~200 cycles rated >> rotational life, or not rated at all. >> >> Any fave longer-life trim pots? >> >> > can't use a regular pot? > > https://www.digikey.com/product-detail/en/bourns-
inc/3310Y-001-103L/3310Y-001-103L-ND/1088215 +1 -- Tim Wescott Wescott Design Services http://www.wescottdesign.com I'm looking for work -- see my website!
On Tue, 09 May 2017 17:20:25 -0400, Phil Hobbs wrote:

> Hi, all, > > I'm doing a lab special for some folks in the physics department of the > University of Oxford. It's an interesting wrinkle on the laser noise > canceller, which is going to work with some HgCdTe photodiodes at 5 > microns. (*) > > These gizmos are probably significantly less linear than silicon diodes, > so I'm giving them an offset current adjust pot so that they can tweak > the cancellation point a little bit. Thus they're going to be adjusting > that pot quite often. > > Trouble is, all the trim pots I can find are ~200 cycles rated > rotational life, or not rated at all. > > Any fave longer-life trim pots?
Something like this, with some good pushbuttons? <http://www.analog.com/media/en/technical-documentation/data-sheets/ AD5228.pdf> This is the first non-Maxim part in DigiKey's search, so there may be better choices. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com I'm looking for work -- see my website!
On Tue, 9 May 2017 17:20:25 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>Hi, all, > >I'm doing a lab special for some folks in the physics department of the >University of Oxford. It's an interesting wrinkle on the laser noise >canceller, which is going to work with some HgCdTe photodiodes at 5 >microns. (*) > >These gizmos are probably significantly less linear than silicon diodes, >so I'm giving them an offset current adjust pot so that they can tweak >the cancellation point a little bit. Thus they're going to be adjusting >that pot quite often. > >Trouble is, all the trim pots I can find are ~200 cycles rated >rotational life, or not rated at all. > >Any fave longer-life trim pots? > >Thanks > >Phil Hobbs > >(*) I'm getting a factor of nearly 10 improvement in cancellation >bandwidth (in the spherical-cow SPICE universe) by putting a bandaid on >the MAT14 supermatch quad NPN. It uses one SiGe:C NPN to make a >Darlington, thereby returning nearly all the base current to the >collector, and another one as a CE stage looking at the MAT14's base and >driving the other SiGe's base to force the MAT14's base to stay still >out to high frequency. I have to put in bias at the MAT14 base and >take it out again from the collectors, but since I need an offset >current pot anyway that's not much of a worry.
We use the Bourns 3314G surface-mount pots. They are very reliable. I think the 200 turn rating is wildly pessimistic, like those 1000 hour electrolytic cap specs. Setting them to 0.1% of rotation is dicey. 1% is easy. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
>I think long life and trim pot, don't belong in a sentence together. >I'll second Lasse and suggest a regular pot.
Looks that way, I agree. Regular pots are normally carbon or plastic, which are easier on the wiper plating but have horrible tempcos. I'll probably just have to burn enough current in the pot that its tempco doesn't matter so much. (The offset adjust circuit is a 200k resistor from the summing node to a 20k pot between +15 and ground, so a 2000 ppm/K plastic pot is a fairly serious inconvenience.) Might need another op amp, and there are six already. :( This circuit has some weird component values, e.g. a 1000 uF cap bypassing a 10-ohm sense resistor in a 100-MHz bandwidth bootstrap. Fun though. Thanks Phil Hobbs
On 2017-05-09 14:20, Phil Hobbs wrote:
> Hi, all, > > I'm doing a lab special for some folks in the physics department of the > University of Oxford. It's an interesting wrinkle on the laser noise > canceller, which is going to work with some HgCdTe photodiodes at 5 > microns. (*) > > These gizmos are probably significantly less linear than silicon diodes, > so I'm giving them an offset current adjust pot so that they can tweak > the cancellation point a little bit. Thus they're going to be adjusting > that pot quite often. > > Trouble is, all the trim pots I can find are ~200 cycles rated > rotational life, or not rated at all. > > Any fave longer-life trim pots? > > Thanks > > Phil Hobbs > > (*) I'm getting a factor of nearly 10 improvement in cancellation > bandwidth (in the spherical-cow SPICE universe) by putting a bandaid on > the MAT14 supermatch quad NPN. It uses one SiGe:C NPN to make a > Darlington, thereby returning nearly all the base current to the > collector, and another one as a CE stage looking at the MAT14's base and > driving the other SiGe's base to force the MAT14's base to stay still > out to high frequency. I have to put in bias at the MAT14 base and > take it out again from the collectors, but since I need an offset > current pot anyway that's not much of a worry. >
Some claim a much higher rotational life but you'd have to obtain hard data first: http://www.globalsources.com/gsol/I/Trimmer-potentiometer/p/sm/1126283314.htm#1126283314 Not sure how they get to 10,000 for rotational life. -- Regards, Joerg http://www.analogconsultants.com/
On Tue, 09 May 2017 17:12:54 -0700, Joerg <news@analogconsultants.com>
wrote:

>On 2017-05-09 14:20, Phil Hobbs wrote: >> Hi, all, >> >> I'm doing a lab special for some folks in the physics department of the >> University of Oxford. It's an interesting wrinkle on the laser noise >> canceller, which is going to work with some HgCdTe photodiodes at 5 >> microns. (*) >> >> These gizmos are probably significantly less linear than silicon diodes, >> so I'm giving them an offset current adjust pot so that they can tweak >> the cancellation point a little bit. Thus they're going to be adjusting >> that pot quite often. >> >> Trouble is, all the trim pots I can find are ~200 cycles rated >> rotational life, or not rated at all. >> >> Any fave longer-life trim pots? >> >> Thanks >> >> Phil Hobbs >> >> (*) I'm getting a factor of nearly 10 improvement in cancellation >> bandwidth (in the spherical-cow SPICE universe) by putting a bandaid on >> the MAT14 supermatch quad NPN. It uses one SiGe:C NPN to make a >> Darlington, thereby returning nearly all the base current to the >> collector, and another one as a CE stage looking at the MAT14's base and >> driving the other SiGe's base to force the MAT14's base to stay still >> out to high frequency. I have to put in bias at the MAT14 base and >> take it out again from the collectors, but since I need an offset >> current pot anyway that's not much of a worry. >> > >Some claim a much higher rotational life but you'd have to obtain hard >data first: > >http://www.globalsources.com/gsol/I/Trimmer-potentiometer/p/sm/1126283314.htm#1126283314 > >Not sure how they get to 10,000 for rotational life.
He has an army of hunchbacks, and can surely buy a few screwdrivers. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Tue, 9 May 2017 16:34:10 -0700 (PDT), the renowned
pcdhobbs@gmail.com wrote:

>>I think long life and trim pot, don't belong in a sentence together. >>I'll second Lasse and suggest a regular pot. > >Looks that way, I agree. Regular pots are normally carbon or plastic, which are easier on the wiper plating but have horrible tempcos. > >I'll probably just have to burn enough current in the pot that its tempco doesn't matter so much. (The offset adjust circuit is a 200k resistor from the summing node to a 20k pot between +15 and ground, so a 2000 ppm/K plastic pot is a fairly serious inconvenience.) Might need another op amp, and there are six already. :( > >This circuit has some weird component values, e.g. a 1000 uF cap bypassing a 10-ohm sense resistor in a 100-MHz bandwidth bootstrap. > >Fun though. > >Thanks > >Phil Hobbs
There are conductive-plastic-over-wirewound pots with ridicuous life but commensurate price tags. -- Bourns 3590 ten-turn WW pots are not as expensive as one might fear. Rotational life is listed at 10^6 turns, and tempco is 50ppm/&#2013266096;C. Because the helical element is long, resolution is high, and you can even get 100K ohms. --sp -- Best regards, Spehro Pefhany