Forums

Trimpot with decent rotational life?

Started by Phil Hobbs May 9, 2017
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.
Encoder and DAC?
>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/&deg;C.
Nice parts, I agree. I don't have a panel to mount them on, but since I have a 200k resistor between the pot and anything sensitive, I might be able to make a big hole in the board to mount the pot. Thanks Phil Hobbs
On a sunny day (Tue, 9 May 2017 17:20:25 -0400) it happened Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote in
<ubmdnZoqPNhgrI_EnZ2dnUU7-THNnZ2d@supernews.com>:

>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?
Real 10 turns front panel pots come to mind, but also do it digital with up / down buttons and a PIC EEPROM memory? Perhaps driving a DAC, or some MOSFETS?
On 05/09/2017 07:00 PM, Tim Wescott wrote:
> 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.
Thanks. I'm not a fan of pushbutton interfaces for tuning stuff, though, and just dumping in another op amp would be cheaper anyway. I'll probably go with a conductive-plastic pot and an OPA197. Cheers Phil Hobbs -- 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
On Wed, 10 May 2017 08:39:53 GMT, Jan Panteltje
<pNa0nStpealmtje@yahoo.com> wrote:

>On a sunny day (Tue, 9 May 2017 17:20:25 -0400) it happened Phil Hobbs ><pcdhSpamMeSenseless@electrooptical.net> wrote in ><ubmdnZoqPNhgrI_EnZ2dnUU7-THNnZ2d@supernews.com>: > >>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? > > >Real 10 turns front panel pots come to mind, >but also do it digital with up / down buttons and a PIC EEPROM memory? >Perhaps driving a DAC, or some MOSFETS?
Nonvolatile DPOTS are cool, but you need to provide an SPI or I2C connector, and software. It's pretty easy to grab a screwdriver or a Swiss army knife and frob a trimpot. DPOTS are slow, too. Trimpots are usable at a GHz or so. A dipswitch is sometimes an alternate to a trimpot, but the pot will be smaller and cheaper and have more resolution. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Wed, 10 May 2017 10:23:54 -0400, Phil Hobbs wrote:

> On 05/09/2017 07:00 PM, Tim Wescott wrote: >> 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. > > Thanks. I'm not a fan of pushbutton interfaces for tuning stuff, though, > and just dumping in another op amp would be cheaper anyway. I'll > probably go with a conductive-plastic pot and an OPA197.
Eh, others were already going down that road -- I thought I'd suggest this one for completeness. I agree with you about buttons, BTW. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com I'm looking for work -- see my website!
On Tuesday, 9 May 2017 22:17:57 UTC+1, Phil Hobbs  wrote:

Trimpot and good twiddle life are contradictory. They're corner cutting devices for when they'll seldom need adjusting. Maybe use a pot.


NT
On Tuesday, May 9, 2017 at 10:19:08 PM UTC-4, pcdh...@gmail.com wrote:
> >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/&deg;C. > > Nice parts, I agree. I don't have a panel to mount them on, but since I have a 200k resistor between the pot and anything sensitive, I might be able to make a big hole in the board to mount the pot.
We use a lot of those too. 1" diameter hole for pot (trim off plastic tabs on pot) and ~1/4" hole centered (somewhere) on the 1" circumference for the solder tabs. George H.
> > Thanks > > Phil Hobbs
On Wednesday, May 10, 2017 at 7:17:57 AM UTC+10, 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.
http://www.farnell.com/datasheets/1911177.pdf No specified rotational life, but much more settable than cheaper parts. I remember specifying a similar part for the Cambridge Instruments electron beam microfabricator. It was more expensive than the part it replaced, but the fact that you could set it precisely meant that final test saved about half an hour on getting the board set up - everybody ended up pleased about that. -- Bill Sloman, Sydney
On Wed, 10 May 2017 16:40:05 -0700 (PDT), the renowned George Herold
<gherold@teachspin.com> wrote:

>We use a lot of those too. 1" diameter hole for pot=20 >(trim off plastic tabs on pot) >and ~1/4" hole centered (somewhere) on the 1" circumference=20 >for the solder tabs.
Next time get slots! Way stronger and easier to solder. https://i.imgur.com/4DWYbKz.png --sp -- Best regards, Spehro Pefhany