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 Post subject: Triplett 630 meter movement
PostPosted: Sep Mon 21, 2015 1:12 am 
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Joined: Sep Mon 21, 2015 12:25 am
Posts: 4
I just bought a Triplett 630-PLK on E-Bay.
The meter is sluggish to respond to the meter zero screw. The needle moves a lot when the meter is moved (much more than my new Simpson 260). If I move the meter between horizontal and vertical the needle settles 2-3 marks on the AC DC scale from zero. And the meter is not good at returning to zero after the meter is moved and returned to the same position.
Does anyone know what the problem is and if it can be fixed?

Ron


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 Post subject: Re: Triplett 630 meter movement
PostPosted: Sep Mon 21, 2015 6:48 am 
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Joined: May Fri 01, 2009 3:53 am
Posts: 1473
Location: Glendale, California
Sounds like worn or dirty pivot jewels to me. If your 260 is new, it of course will not experience the same symptoms as this Triplett, because Simpson has been using taut-band suspension movements since at least the 1970's, which are a frictionless movement.

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Unemployed Analog Meter Technician. Simpson 260 specialist.

John, KK6WHY


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 Post subject: Re: Triplett 630 meter movement
PostPosted: Sep Mon 21, 2015 11:30 pm 
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Joined: Sep Mon 21, 2015 12:25 am
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The Triplett is a 630-PLK Type 9 Taut Band. I don't know how old it is. Pivot jewels sounds expensive or unfixable. I'm attaching 2 pictures in case they help.
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WIN_20150921_154033 (2).JPG [ 86.16 KiB | Viewed 2492 times ]


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 Post subject: Re: Triplett 630 meter movement
PostPosted: Sep Mon 21, 2015 11:41 pm 
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Joined: May Fri 01, 2009 3:53 am
Posts: 1473
Location: Glendale, California
the 630-PLK type 9 is not old at all.

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Unemployed Analog Meter Technician. Simpson 260 specialist.

John, KK6WHY


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 Post subject: Re: Triplett 630 meter movement
PostPosted: Sep Tue 22, 2015 5:17 pm 
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Joined: Sep Mon 21, 2015 12:25 am
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From what we have so far it sounds like there is something wrong with the meter movement - maybe weak magnets.
I played with the new Simpson and it also took some turning before it responded to the adjusting screw so I guess that is normal but it returns to zero when moved or re-positioned.

Can someone post on how well an old Triplett and a new Triplett return to zero when the meter is stood up and then laid down? I did not have to mess with adjusting on the Triplett I used in the 1970s.

I called a local calibration lab and they said it is $87 to calibrate a Triplett or a Simpson but they do not repair, and this would be considered repair, so replace or live with constant re-zeroing.

I have a short time to return the meter for a refund and be out $30 for shipping. This is one of the new-other Tripletts currently on E-Bay from coautomation that came from Connecticut Dept. of Education and in the pictures they are all off zero. This leads me to think they were zeroed lying down and lost it when stood up. So maybe all new Tripletts are like this. Does anybody Know?

Ron


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 Post subject: Re: Triplett 630 meter movement
PostPosted: Sep Tue 22, 2015 8:55 pm 
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Joined: May Fri 01, 2009 3:53 am
Posts: 1473
Location: Glendale, California
The meter should not vary from zero more than a division or two between a flat and vertical position. If it does, the meter needs to be balanced.

On most 630s, there is a large capacitor across the movement, which can slow the meter down, especially if it's leaky. That being said, if the meter does not return to zero properly without some tapping, it probably has worn or dirty pivot jewels, or debris in the meter gap. A weak magnet would not cause the symptoms you describe, but rather would just affect the overall accuracy.

Sounds like the shop you called is only a metrology/calibration shop, and does not have any meter technicians on staff. Most calibration shops are like this.
There are shops that actually repair meters. I work for one, and there are a few others as well.

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Unemployed Analog Meter Technician. Simpson 260 specialist.

John, KK6WHY


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 Post subject: Re: Triplett 630 meter movement
PostPosted: Sep Tue 22, 2015 10:16 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1982
Location: Oswego, NY, USA
I remember seeing that same (Ebay, I think?) set of auctions, from a Dept of Education with a "calibration sticker" & needles far off zero (in any position, w/o its test leads connected to an external signal)...either one of those would probably tell me to pass, knowing there's a high chance they were bumped around or dropped on a floor. As cwr mentioned, one speck of dirt in the gap can cause needle sticking or zeroing not reproduceable.


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 Post subject: Re: Triplett 630 meter movement
PostPosted: Sep Wed 23, 2015 12:45 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 12437
Location: Powell River BC Canada
Do an all range calibration check with the meter laying flat, and the pointer zero'ed.

Dos it act un damped when you shift it in air , with the meter switched to off ?

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VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
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 Post subject: Re: Triplett 630 meter movement
PostPosted: Sep Wed 23, 2015 6:46 am 
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Joined: Sep Mon 21, 2015 12:25 am
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I did the best calibration check I could with a good assortment of resistors and a 30v variable DC supply and it looks good.
When shifted in the air the needle swings close to 2 on the 10v scale (which seems loose compared to Simpson) but after the first swing there is only 1 or 2 very small swings.

The case is not chipped or scratched - looks new. Considering E-Bay's definition of new-other (like new) I hoped it had been sitting in a stock room and not used in a classroom.

From flat to vertical the meter moves 2 1/2 divisions so it probably does need to be balanced. The Simpson stays zeroed and if I remember so did the old Tripletts, but that was a long time ago.


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 Post subject: Re: Triplett 630 meter movement
PostPosted: Sep Wed 23, 2015 10:12 am 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 10256
Location: Long Island NY
The zero set should not change more than a pointer width between horizontal and upright vertical position on any of the Triplett 630 meters. Unfortunately, despite being in good physical condition, it sounds like your meter was dropped or roughly handled at some point in its life, and one of the balancing weights may have shifted. This can be fixed, but it takes a gentle hand and some time and patience.

But there's a secondary issue here, which is the pointer not returning to the same place after an excursion. One should not try to balance a movement unless it returns to zero correctly. Your meter is a taut band type, so there are no pivots or jewels to be concerned with. Does the meter seem like it is sticking? If so there could be debris between the armature and the core or the poles. If it seems like it takes forever to get back to the same zero point, but it eventually does without tapping or other "help," then the meter is probably okay but being damped by something in the circuit. It's probably not the taut bands, as the calibration would be off if they had lost their strength. Static build-up on the plastic front cover can often make a meter seem it's got serious problems; to find out, just wipe it down with a cloth that has been dampened with water and a tiny dab of dish detergent and any static build-up should be gone. Static is usually more of a problem in the winter, but this summer has been unusually dry in many parts of the country, so it has to be considered--especially if your meter was packed in styrofoam peanuts.

To check and adjust the balance, the meter is first put flat on its back and zeroed using the mechanical adjuster. Then hold it vertical and rotate it to the left so the pointer is exactly horizontal, e.g. pointing at 9:00 on an imaginary clock dial. It should still be at zero on the scale. If not, the tail weight--opposite the pointer--is out of adjustment. Then rotate the meter to the right until the pointer is exactly vertical, pointing at 12:00. Again, it should still be at zero. If not, one of the side arm weights--the ones at 90 degrees to the pointer--needs adjustment. Note that some meters cannot be balanced perfectly this way, in which case the proper way to set them is to split the difference between the vertical and horizontal pointer positions. That way, the meter pointer should stay on zero with the instrument flat on its back or upright.

On modern meter movements, the weights are usually little coils of wire that have a bend or curvature to them that holds them on the arm. If you squeeze them gently with tweezers, they'll slide on the arms easily unless somebody has glued them in place. Never force anything on a meter movement! If the weights have been glued, they may break off before they move again. In that case, the best strategy is to see if a drop of paint on one of the arms can bring it into balance.

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 Post subject: Re: Triplett 630 meter movement
PostPosted: Sep Wed 23, 2015 3:46 pm 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 12437
Location: Powell River BC Canada
Another thing to try is to electrically reset the pointer after it has moved from zero
after moving the meter.

Use a small voltage or current, from a bridge source capable of shifting the pointer
above and below zero. Try it on a few ranges. If you can reset zero this way, then it is
a mechanical stiction, or as was previously suggested dielectric retention in a movement
damping capacitor.

Also consider electrostatic zone condition in the plastic face. Those can be strange sometimes.

If you continue to use the zero screw, eventually you will break it. (how do I know this )

I own three 630s, all have issues. The most modern one is a 630NA.

They are good for measuring high voltage DC without a multiplier probe. (60 megohm
loading). A spark over cant zap them or scramble their brains like digital types.

_________________
de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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