optical knob encoder: HP/Agilent 33120A freq generator, tuni

[whit3rd]

On Monday, August 8, 2011 3:12:54 AM UTC-4, Winfield Hill wrote:

We have about 10 Agilent 33120A frequency-generator / synthesizers
in our lab, and a few other similar synthesizers. They feature a
convenient digital frequency and amplitude programming knob that's
based on optical encoders.
....
Since they use an optical 2-bit quadrature grey-code ...

But recently I've encountered two instruments with identical
tuning-knob failures...

In both cases the knob seems 'stuck"

There's two optointerruptors out-of-phase with a toothed wheel (or
somesuch, like in the old mice). Your symptom is of one blocked
or dim lamp.

 

[N_Cook]

N_Cook <diverse@tcp.co.uk> wrote in message
news:j1uar2$4ng$1@dont-email.me...

Jeff Liebermann <jeffl@cruzio.com> wrote in message
news:636547tj5afpqe0hcfof68lqjijfar40gr@4ax.com...
On Wed, 10 Aug 2011 08:17:53 +0100, "N_Cook" <diverse@tcp.co.uk
wrote:

A job for tomorrow is to take some measurements of one of those tiny
preset
size pots.
The wiper arcs are something like 3 off 10mm long , and section .2x.4mm
IIRC
but I will try and measure the contact force , I'm guessing at this stage
of
order 10 gm. Once one wiper lifts I imagine its not long before all 3 lift
at some part of their travel.

Alpha type 4D3-11 pot , footprint 9.6x 11.2mm. 2 wiper arcs about 7 and 9 mm
long. Wiper metal 0.1mm thick x 0.3mm.
Could not measure contact force in-situ. With wiper removed from recess, 10
gm would visibly move one wiper relative to the other. No visible track
scoring under a x30 magnification.
Of course , those old enough, would have come across the effect of hardening
grease in cassette tape mechanisms then VCR. Where an arm pivots on an axle
and return action is just a light torsion spring.

 

[Wild_Bill]

FWIW, the acrylic "body" of manu LEDs can be resized.. and leaving the
emitting surface area untouched generally won't reduce the output.

I've reduced the diameter of common LEDs to fit where they normally
wouldn't. The tiny emitting chip is very small compared to the size of the
outer diameter of the acrylic.
A pin vise can be used to hold the leads of a common (thru-hole) LED.

There are some applications where the tiny chips are used without acrylic
bodies, and the very fine gage gold leads are attached directly to gold
plated circuit board pads.
A home bathroom scale had what looked like a 3-digit 7-segment display, but
the separate LED chips were mounted to the board, and a plastic housing was
placed over the LED chips (with colored film) which made it appear to be a
normal 3-digit module.

--
Cheers,
WB
..............


"JW" <none@dev.null> wrote in message
news:hf1247dibv5bnd3d416ug4b35rlacr7g65@4ax.com...

And what a pain in the butt to get to on a 6034A! I wish I could find a
"side firing" LED that would not only fit in that little slot, but also be
the right wavelength for it to work correctly. I've experimented a bit
with this, but never been successful.

 

On Aug 8, 1:19 am, "N_Cook" <dive...@tcp.co.uk> wrote:

Winfield Hill <Winfield_mem...@newsguy.com> wrote in message

news:j1o29m0k83@drn.newsguy.com...

We have about 10 Agilent 33120A frequency-generator / synthesizers
 in our lab, and a few other similar synthesizers.  They feature a
 convenient digital frequency and amplitude programming knob that's
 based on optical encoders.  A pair of left-right pushbuttons sets
 which decade you're adjusting with the knob, and over or underflows
 operate on the next higher decade.  There's a little indent near
 the edge of the knob so you can spin it with your fingertip.  You
 can also use up-down pushbuttons or directly punch in numbers, but
 the spinning knob is very convenient.  Typically such encoders have
 16 or 32 ticks per revolution.  A very nice design feature.

 The optical shaft encoders were originally made by HP, but now of
 course they're made by Avago. Sometimes they call these a digital
 potentiometer or a "Panel Mount Optical Rotary Encoder".  For
 example, the HRPG-AD16 product line, about $34 each at Mouser.

 http://www.mouser.com/Search/Refine.aspx?Keyword=HRPG-AD16

http://www.avagotech.com/pages/en/motion_control_encoder_products/rot...
tches/hrpg-ad1616c/





 Since they use an optical 2-bit quadrature grey-code (as opposed
 to using a pair of switch contacts), they're supposed to be
 extremely reliable.

 But recently I've encountered two instruments with identical
 tuning-knob failures, one in an elegant 33250A 80MHz model
 that's on my bench, and the other in one of our standard
 33120A 15MHz instruments.

 In both cases the knob seems 'stuck" and not to work as you
 turn it, except every now and then you'll get one or two
 increments or decrements.  Totally useless.

 I'm wondering if anyone else has encountered this failure?

--
 Thanks,
    - Win

Its probably patentable so is there a patent outline for them somewhere, to
show what the innards are?

Lots of video editing gear uses optical shaft encoders. Typical
failure is bushing wearout that alters the alignment of the rotary vs
fixed disk. You'll find excess axial 'play' and often side-side play
as well. Some decent lubricant early on sold have increased the life.

G˛

 

[Michael A. Terrell]

stratus46@yahoo.com wrote:

Lots of video editing gear uses optical shaft encoders. Typical
failure is bushing wearout that alters the alignment of the rotary vs
fixed disk. You'll find excess axial 'play' and often side-side play
as well. Some decent lubricant early on sold have increased the life.

Have you ever tried the Griffin Powermate? It has a lot better feel
that the old Panasonic jog wheels I used to use to edit video.


--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

 

[Jeff Liebermann]

On Wed, 10 Aug 2011 17:15:35 +0100, "N_Cook" <diverse@tcp.co.uk>
wrote:

Of course being a seller of lubricants there is no tabling of the long-term
performance as far as immunity to hardening.

NYE also sells laser printer fuser grease. After several aborted
attempts at finding a cheaper substitute, I've resigned myself to
using the overpriced real thing.

In a past life, I designed marine radios. Pots were always a problem.
If "sealed", they would eventually condense some water out of the air,
and rot. If vented, salt encrustation and corrosion would become a
problem. Sealing the shaft was a big help, but re-lubrication was
tricky.

However, ignoring all these mechanical problems, we did have problems
with the grease on the resistance material. It would develop dead
spots, where the wiper would not make contact, usually where the
volume and squelch controls spent most of their time. It was
obviously a lump of grease that the wiper was riding on top of, but
what was the cause?

Basically, silicon grease (PDMS) will absorb small amounts of water
and aromatic solvents. These bring with it salt from the marine
atmosphere. The salt crystallizes out of solution, the grease
encapsulates it, and we have a lump. I played around with various
microscope filters for hours until I could see the tiny salt crystals
imbedded in the grease. Nye sent us some sample greases, which were a
big improvement and which became standard for re-lubrication.

That "velvet feel" becoming
gumming up the works

<http://www.nyelubricants.com/products/damping.shtml>

You won't appreciate proper pot lube until after you try to operate a
mobile radio or HT when it's really cold, and find all the controls
stuck in place due to thickening of the lubricant.

And pot track lubrication being insufficient to cause
"aquaplaning" and then with aging/ chemical reaction, hardening and forming
a wedging under the wiper and so loosing contact for all or most of the
track run.

I've never seen this wedging. I have seen salt lumps formed when the
pot is left in one position for long periods, in a hostile atmosphere.

A job for tomorrow is to take some measurements of one of those tiny preset
size pots.
The wiper arcs are something like 3 off 10mm long , and section .2x.4mm IIRC
but I will try and measure the contact force , I'm guessing at this stage of
order 10 gm. Once one wiper lifts I imagine its not long before all 3 lift
at some part of their travel.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[N_Cook]

Jeff Liebermann <jeffl@cruzio.com> wrote in message
news:kbv747tj6j1e0qf13cf77lb41b2tr7kdq2@4ax.com...

On Wed, 10 Aug 2011 17:15:35 +0100, "N_Cook" <diverse@tcp.co.uk
wrote:

You won't appreciate proper pot lube until after you try to operate a
mobile radio or HT when it's really cold, and find all the controls
stuck in place due to thickening of the lubricant.

Easily dissimilar metals , Al and brass and sliding fit , then the naval
saying.
Cold enough to freeze the (iron canon) balls off a brass monkey (trivet)

 

[Spehro Pefhany]

On 8 Aug 2011 00:12:54 -0700, the renowned Winfield Hill
<Winfield_member@newsguy.com> wrote:

We have about 10 Agilent 33120A frequency-generator / synthesizers
in our lab, and a few other similar synthesizers.

Hey, Win:-

We had a mechanical encoder failure on a 33220A arb function
generator. It is a known issue with these encoders and Agilent sent a
repair kit gratis (or we could have sent it in). It's an easy fix, so
I elected to do it myself.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

 

[JW]

On Fri, 12 Aug 2011 19:36:51 -0400 Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote in Message id:
<o3eb47dskudopktv8amu3tsis95lmf9elo@4ax.com>:

On 8 Aug 2011 00:12:54 -0700, the renowned Winfield Hill
Winfield_member@newsguy.com> wrote:

We have about 10 Agilent 33120A frequency-generator / synthesizers
in our lab, and a few other similar synthesizers.

Hey, Win:-

We had a mechanical encoder failure on a 33220A arb function
generator. It is a known issue with these encoders and Agilent sent a
repair kit gratis (or we could have sent it in). It's an easy fix, so
I elected to do it myself.

Here's the service note:
http://cp.literature.agilent.com/litweb/pdf/33220A-02B.pdf
The expiration for free service or parts is February 1, 2012.