Background
Description
    Weston Model One
    Weston Model 30 Sensitive Relay
    Weston Sensitrol Relay
    Leeds & Northrup 2420-A Galvanometer
Photos
    Weston Model One
    Leeds & Northrup 2420-A Galvanometer
    Leeds & Northrup 2420-C Galvanometer
Patents
Related
References
Links

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Background

For some years I've been looking for a copy of the book: Measuring Invisibles by Weston Electrical Instrument Corp. (Measuring Invisibles) and during March 2020 I got a 1938 hardback version.  On page 12 is a photo of Model One, Number One.  So I looked to see if any Model Ones were available and found one on eBay.  I choose this particular meter because there was a change it had a patent data plate, which turns out to be the case.  Other meters had a simpler label even though they were also Model One meters.  Current, Voltage and Light are all invisible, hence the title.
This is Model One No. 44506.  In their advertising they say the model numbers do not change every year.

While searching out all the patents listed (see Fig 2) I discovered why sometimes you see patent dates but not patent numbers.  In this case by using patent dates they save a lot of space since in many cases more than one patent is issued on the same date.

Also see how a Helmholtz coil will deflect a compass.

Description

Weston Model One

The first needle type meter movement made by Weston based on patents between 1888 and 1901 as shown on the label.  Note that patent dates are shown not patent numbers.  This saved space since there were often more than one patent granted on the same day (always a Tuesday).  Some of the earliest patents were for a Reflecting Galvanometer which sparked an interest in getting one of them.  Many of them on eBay had photos showing broken coil suspensions, i.e. not at all in working condition.  The L&N 2420-A seemed to be a much more rugged design, so I got one of them.

Ohms Table (to + terminal)

Terminal	Ohms
1500 mA	0.0?
150 mA	0.2
15 mA	2.0
150 V	22k64
750 V	113k3

Weston Model 30 Sensitive Relay

This appeared on eBay in Feb 2022 and the following patent dates could be read:

Image	No.	Title	Inventor	Assigned	Date	Class
					Nov 6, 1888
					May 14, 1889
					Apr 29, 1890
					Feb 17, 1891
					Dec 19, 1893
					Oct 4, 1898
					Jul 16, 1901

FTL Design: Weston Electrical Instrument Corporation Model 30 Sensitive Relay - wood box unit s/n: 427 & Bakelite unit s/n: 11020.  Both show the above 7 patents.
Harvard: Collection of Historical Scientific Instruments: sensitive DC relay, Weston model 30 - 20 uA controls 0.1A current.

Weston Sensitrol Relay

This is a very sensitive relay which AFAICR could be operated directly from a Weston Model 594 Photronic Cell.

Is KS-7901 a telephone specification, like KS8455?  Let me know. Not at the TCI Library.

Photos

Fig 1

Fig 2 Looks like Red & Black wires in center tube; relay coil? Terminal posts numbered 1 to 5.

Fig 3 Terminals 4 & 5 are outer contacts.

Drawing		Patent
		2014385 Electrical control device, Anthony H Lamb, Weston Electric Instrument Corp, 1935-09-17, 361/157 -
		2014386 Sensitive control device, Anthony H Lamb, Weston Electric Instrument Corp, 1935-09-17, 361/157 -
		2014387 Relay system, Anthony H Lamb, Weston Electric Instrument Corp, 1935-09-17, 361/157; 200/7 -
		2014388 Sensitive relay device, Anthony H Lamb, Weston Electric Instrument Corp, 1935-09-17, 200/56R -
		2062915 Control device, Anthony H Lamb, Weston Electric Instrument Corp,1936-12-01, 335/150; 307/41; 307/102; 307/104; 318/122; 318/443; 318/448; 318/686; 335/179; 338/116; 338/150; 361/157 -

  YouTube: Applied Science: Vintage electrical tech - Weston Sensitrol Relay - two of the contacts are for a solenoid that brings the needle back to zero. Pin Out?  - Link to YouTube courtesy of  Steve Cichorsky.

http://n4trb.com/AmateurRadio/SemiconductorHistory/Electronic%20Shortcuts%20for%20Hobbyists.pdf - from Ed Sharpe of SMECC.

Leeds & Northrup 2420-A Galvanometer

This Reflecting Galvanometer contains not only the reflecting galvanometer but also a light source, lens with pointer mask and provision for a fine wire across the lens at the tip of the pointer.  This way a beam of light shines out of the rectangular slot.  So all that's needed is a horizontal yardstick (meter stick) for the light to shine one.

From what I've read the sensitivity of this instrument is much higher than of a needle type meter of similar vintage.

Leeds & Northrup Co. Catalog 1925 Physics Instruments: "These galvanometers are completely portable and have a sensitivity some twenty times that of the best pointer type portable galvanometers.  They require no leveling.  They are much more convenient than other reflecting galvanometers, and will withstand as much rough usage as an ordinary millivoltmeter.  The scale illumination is such that they are easily read in daylight."

Ohms Table (to + terminal)

Terminal	Ohms
1500 mA	0.0?
150 mA	0.2
15 mA	2.0
150 V	22k64
750 V	113k3

Photos

Weston Model One

Fig 1	Fig 2 Patent numbers	Measuring Invisibles
Fig 3	Fig 4	Fig 5

Leeds & Northrup 2420-A Galvanometer

Looking for manual, documentation, years when on market, catalog entry, &Etc.
Looking for a Catalog of  Leeds & Northrup instruments by L&N Model number. Let me know.
This Harvard L&N 1903 - 1995 page lists many interesting documents, but they are all 404 Not Found.
 HarvardL&N Collection: L&N 2420,

Fig 1 Missing either a ground glass meter face or a clear glass to keep out dust.  Let me know. Cat. No. 2420-A,  Serial No. 422628	Fig 2 Horseshoe magnet provides field for galvanometer. Lamp at left shines through lens with pointer mask with fine wire. Light bounces off Galvanometer mirror and shines on ground glass or out clear glass?	Fig 3 Solder spots on lens frame for fine wire. Front terminals for lamp. Rear (shorted to ship) terminals for Galvanometer. WM?193.
Fig 4 What does the black knob do when turned? Let me know.	Fig 5 Rear metal ID plates. GSID265014 S8 U.S. Government, Contract# W-2279-SC-17, Project 2B Property L/200/00	Fig 6 lamp powered. back of business card in glass slot. The fine wire is missing from the pointer. There is considerable dampening of the zero adjustment (black knob).

Leeds & Northrup 2420-C Galvanometer

Photos from Dan Graybeal
Note the optical system is different from the "-A" version in that the lens and surrounding ring with pointer and fudicial wire is missing.  Maybe incorporated into the fancy lamp?

Fig 1 Note missing lens assembly.

Fig 2  Does this lamp include optics? Is this a line source of light?

Fig 3 I think this is a replacement for the factory frosted glass scale. Note paper is on front side and numbers read correctly.

Patents

Weston

Because the dates are very difficult to read, after getting the list of patent dates, I used an on line calendar to check that the issue date was a Tuesday.  Those that were not I re-read using a magnifying glass and guessed at a different date until it came out on a Tuesday.  There were over a half dozen in error.

DOW	Date	No.		Title	Class	Comment
Tu	Oct 21, 1884	307031		Electrical Indicator, T. A. Edison, copied to here 30 Dec 22 from: One Tube Radio \ Tube History		both meter and vacuum tube
Tu	Sept 11, 1888	389274		Standard tangent-galvanometer	324/97 324/154R	not listed on Mdl 1
Tu	Nov. 6, 1888	392385 392386 392387 392476 392477 392478		Electroplated Coil for Electrical Measuring Instrument Electrical Measuring Apparatus (damped Moving Coil) Electrical Measuring Apparatus (damped Moving Coil) Reflecting Galvanometer Galvanometer "	324/144; 335/299; 336/82; 336/195; 310/194; 336/73; 336/84R 324/115 324/115 324/97; 324/154R 324/97 "	-
		400980		Standard tangent-galvanometer		not listed on Mdl 1
Tu	May 14, 1889	403311 403312		Electrical Measuring Instrument (2 scales: 0-100 & 0-5) Portable Tangent Galvanometer (Wiki & Helmholtz coil)	324/115 324/97; 159/28.3; 324/154R
Tu	April 29, 1890	426992 427022		Electrical measuring instrument (Balancing temp rise) Electrical measuring instrument (improvements to 392387) + mirrored scale	324/144 324/146; 324/154R; 324/115; 359/439
	Aug 5, 1890	433637		Electrical measuring instrument RE-issued as RE11250 Jun 28, 1892	324/144
Tu	Nov 11, 1890	440291		Index-controlling device for electrical measuring-instruments	324/155; 116/297
Tu	Feb 17, 1891	446489 446490 446491 446492 446493 446494		Electrical measuring instrument Rheostat Electrical measuring instrument Electrical measuring instrument Electrical measuring instrument Electrical measuring instrument	324/151R; 177/DIG.9 338/148; 336/45; 336/139; 338/196 324/144 324/127 324/145 324/145
Tu	May 12, 1891	452326		Electrical measuring instrument	324/144
Tu	Dec 29, 1891	466087		Temperature-regulating device for electrical circuits	324/105; 374/183
Tu	Mar 8, 1892	470340		Movable coil for electrical measuring-instruments	324/155; 336/205; 336/125
Tu	Apr 26, 1892	473538 473539		Electrical measuring instrument Electrical measuring instrument	324/145; 335/279 324/145; 74/99A
Tu	Jun 28, 1892	RE11250		Electrical measuring instrument (AC movement) Also see 433636 Aug. 5, 1890 above.	324/144
Tu	Aug 16, 1892	480894		Electrical measuring instrument	324/155
Tu	Nov 22, 1892	486689		Electrical measuring instrument	324/144
Tu	Jan 31, 1893	490699 490700 490760		Recording Ammeter Electrical measuring instrument Electrical measuring instrument	346/31; 324/100 324/106 324/144
Tu	Apr 4, 1893	494828 494829 494830		Electrical measuring instrument Recording Voltmeter Ground-detector for electric circuits	324/106 346/31; 324/100; 324/113; 178/95 324/140R; 324/509
Tu	May 2, 1893	496500 496501		Electrical measuring instrument Shunt for Electrical Measuring Instruments	335/148; 324/154R 338/49; 324/126; 338/326; 338/315
Tu	May 16, 1893	497521? 497522?		Electrical measuring instrument Galvanometer A.H. Hoyt assigned to Weston?	324/146; 310/190; 123/634 324/146
Tu	Jun 13, 1893	499313		Electrical measuring instrument	324/144
	Dec 19, 1893	511005		Telegraphic relay	335/148	Model 30?
Tu	Jul 10, 1894	522948 522949 522950		Electrical measuring instrument Watt Meter Watt Meter	324/144; 177/DIG.9 324/142 324/114; 324/156
Tu	Nov 20, 1894	529434 529435		Electrical measuring instrument Electrical measuring instrument	324/144 324/151R
Tu	Jan 29, 1895	533107		Electrical measuring instrument	324/144; 324/150
	Mar 22, 1898	600981 600982 600983		Electrical measuring instrument	324/157	not listed on Mdl 1
Tu	Oct 4, 1898	611722 611724		Electrical measuring instrument Electrometer	324/155; 116/330
Tu	Jul 16, 1901	678706 678707 678708		Electrical measuring instrument Art of manufacturing movable coils for use in connection with electrical measuring instruments "	324/155 29/595 29/564.1; 29/761; 33/613; 269/47
		730061		Reflecting Galvanometer	324/97	not listed on Mdl 1
Tu	Jun 10, 1890	D19895		Case for electrical instruments
Tu	Mar 20, 1894	D23141		Case for electrical instruments
Tu	Mar 27, 1894	D23156 D23157		Supporting-frame for electrical instruments
Tu	Mar 22, 1898	D28394 D28395 D28396

Leeds & Northrop

Apr 4, 1893	494964		Galvanometer	324/97
Jun 20, 1905	792843		Galvanometer (model 2239 wall mount - fragile) (Ref: L&N Prism 2178) Scpoe probably folds up against wall like prior patent 561919	324/97
Feb 5, 1907	843414		Optical reading device for electrical measuring instruments - microscope and reflected optical path	324/97 359/226.2 353/40 359/439

L&N 2420 Galvanometer

Did not find one.

Lord Kelvin (William Thompson) Patents

, W. Thompson (Wiki)

Date	No.	Drawing	Title	Class
Nov 12, 1878	209942		Reflecting Galvanometer Iron Box: B Mirror: i Zero adjust Permanent magnets: K & L	324/97 oldest galvanometer patent in class
March 3, 1902	696117		Apparatus for indicating and recording electric pressure and current Rather than a lab instrument this appears to be for use in the field to measuring DC power either at power stations or loads.	346/17; 346/49; 346/127
Aug 5, 1902	706361		Instrument for measuring electric currents Note must be positioned as shown so that gravity will be part of action. Many early galvanometers depended on gravity. They may have adjustable feet, bubble levels, &Etc.	324/145

String Galvanometers

Devoted to Medical and scientific uses.  In the time before vacuum tubes getting a lot of sensitivity was important.  These units have provision for many permanent magnets.

This term shows up in early Electrocardiograph patents.

1416824 Galvanometer, C.F.. Hindle, not assigned, 1922-05-23, 324/97; 324/144 -

1702650 Galvanometer, F.O. Hindle, Cambridge Instrument Co, 1929-02-19, 324/97  -

1942027 String galvanometer, F.O. Hindle, American Scientific Inst Co, 1934-01-02, 324/97 - This is decades newer than the Thompson patents, so has a different purpose.  This one is easier to use and maintain than prior art string galvanometers.

Related

Weston Model 594 Photronic Cell - Light meters
Integrating Sphere & light sources and sensors

References

Links

PRC68, Alphanumeric Index of Web pages, Contact, Products for Sale
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