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Author Topic: curious Triplett behavor  (Read 1291 times)
WB4SPT
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Posts: 141




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« on: March 27, 2012, 02:36:41 PM »

I've got now a fine Triplett 630HS.  On its back, it reads accurately.  Moved upright, the zero set is quite a bit off, but even when that is reset, now the DC volts is about 5% low.  ANyone see this before?
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AC5UP
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« Reply #1 on: March 27, 2012, 03:39:17 PM »

Moved upright, the zero set is quite a bit off, but even when that is reset, now the DC volts is about 5% low.

The meter was dropped hard enough for the meter movement to become mis-aligned. What you're seeing is some extra slop in the jeweled bearings, a magnet assembly that's no longer symmetrical relative to the armature, or both. That's why the difference between horizontal and vertical. A very skilled hand might be able to un-bend the movement to like-new accuracy but a typical hand would replace the meter movement. The rest of us would decide if horizontal or vertical was the default position and adjust the front panel meter zero screw to compensate.

Assume the meter is no longer linear, less than factory spec accurate, and use it for ballpark readings.............
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K7KBN
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« Reply #2 on: March 27, 2012, 04:26:27 PM »

Another possibility is that the balance weights on the movement arms are not properly adjusted (which is often the case when an analog meter gets dropped.  Part of the certification process we followed in the Navy Cal Lab where I worked half a lifetime ago was to check the balance in three axes and adjust the weights as necessary.  With newer taut-band suspension (TBS) movements there are no pivots and jewels, but the balance weights are still there and still require checking as part of calibration and certification.  Some calibration facilities will do minor internal adjustments and repairs.  Some, however, will just return the instrument as "defective".
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73
Pat K7KBN
CWO4 USNR Ret.
W6EM
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« Reply #3 on: March 27, 2012, 06:27:42 PM »

Another possibility is that the balance weights on the movement arms are not properly adjusted (which is often the case when an analog meter gets dropped.  Part of the certification process we followed in the Navy Cal Lab where I worked half a lifetime ago was to check the balance in three axes and adjust the weights as necessary.  With newer taut-band suspension (TBS) movements there are no pivots and jewels, but the balance weights are still there and still require checking as part of calibration and certification.  Some calibration facilities will do minor internal adjustments and repairs.  Some, however, will just return the instrument as "defective".

I'd agree here, especially with respect to the weights having shifted.  The bearings are probably OK, otherwise the movement would stick or not move at all.

The problem with taught bands is that the inertia of the coil and moving core are such that when dropped, bang, and its usually all over.  I just bought a GE wide view 100uA movement for parts and when I removed the face, the bands were snapped as I thought.  At least with bearings, you might get lucky and be able to reseat the movement if you back off the bearing screws on both sides of the movement.

73,

Lee
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K7KBN
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« Reply #4 on: March 27, 2012, 09:32:32 PM »

Lee -

In about 1969, when the Navy was going with TBS movements on new and replacement switchboard meters, several of us meter mechanics got sent to a school in Dayton where we actually were trained in disassembling the movements and replacing the bands!  In those days I had eyes and hands that worked a LOT better than they do today... Grin
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73
Pat K7KBN
CWO4 USNR Ret.
WB4SPT
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« Reply #5 on: March 29, 2012, 02:35:19 PM »

Lee -

In about 1969, when the Navy was going with TBS movements on new and replacement switchboard meters, several of us meter mechanics got sent to a school in Dayton where we actually were trained in disassembling the movements and replacing the bands!  In those days I had eyes and hands that worked a LOT better than they do today... Grin

Well;  I have a lot of respect for that work now.  My past includes a bit of surface mount rework, and design, but this Triplett TBS defeated me.  I tried a touch of epoxy to add weight but it surprisingly shifted zero even when the pivot was vertical.  Went in a bit deeper, and bad things started to happen, sticky behavior, taunt band got out of align, more scratches on the dial, bent needle.... Oh well, a $10 lesson and I'm still amazed at how much manufacturing labor you got back in the day..
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AC5UP
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« Reply #6 on: March 29, 2012, 02:59:50 PM »

Some days you're the eagle, other days you're the mouse...............

http://wonkette.com/wp-content/uploads/2012/03/eagle_eating_mouse_head-250x217.jpg
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W6EM
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« Reply #7 on: March 29, 2012, 06:03:08 PM »

Lee -

In about 1969, when the Navy was going with TBS movements on new and replacement switchboard meters, several of us meter mechanics got sent to a school in Dayton where we actually were trained in disassembling the movements and replacing the bands!  In those days I had eyes and hands that worked a LOT better than they do today... Grin

Wow.  That's cool, Pat.  Thanks for your service.  They/you must have had some really good magnifiers as well to help out.  I've had shaky hands for years, so I'm not the right guy to be attempting much more than a zero adjustment, let alone fiddling with the weights.

As for the Triplett, there was a guy a few days back selling spare meter parts on eBay.  Meter movements, faces, etc.  Can't find it now, but maybe something like that will be offered again.

Digital meters are nice, but you can't easily see minimums and maximums and dips too well without a pointer.

My favorites are the old Western Electric panel meters that have about 180 or more degrees of scaling around the center of the face.  Like everything Ma Bell used to make, built like tanks. 
 
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