US2548176A

US2548176A - Amplifier

Info

Publication number: US2548176A
Application number: US62746A
Authority: US
Inventors: Paul T Semm; Robert T Nakasone
Original assignee: WHEELCO INSTR Co
Current assignee: WHEELCO INSTR Co; WHEELCO INSTRUMENTS Co
Priority date: 1948-11-30
Filing date: 1948-11-30
Publication date: 1951-04-10
Anticipated expiration: 1968-04-10

Description

Patented Apr. 10, 14951 UNITED STATES PATENT AMPLIFIER Application November 3l), 1948, Serial No. 62,746

OFFICE -2 Claims.

Our invention relates to an improved amplier for slowly varying currents or signals.

It is frequently desirable to amplify slowly varying currents or signals, such as the signals achieved from a photoelectric cell exposed to light of slowly varying intensity. Mechanisms for this purpose haveheretofore been difiicult and expensive in construction since they have either involved D.C. amplifiers with the attendant requirements of critically stable tube characteristics and applied voltages, or chopping devices to convert the D.C. signal to an alter nating wave.

` In accordance with the present invention, the

foregoing problems are covercome and improved operation is secured by providing a saturable reactor energized by the slowly varying current. This reactor is connected in a bridge circuit energized by alternating current. The resultant voltage is rectified and fed back to the reactor.

It is therefore a general object of the present invention to provide an improved amplifier suitable for use in amplifying current changing slowly with time.

Another object of the present invention is to provide an improved amplifier for use with a photo-cell.

Still another object of the present invention is to provide an improved sensitive amplifier for slowly varying signals that requires no chopper or like device and does not demand tubes having particularly stable characteristics or voltage supplies having a high degree of stability.

The novel features which we believe to be characteristic of our invention are set forth with particularity in the appended claims. My invention itself, both as to its organization and method of operation, can best be understood by reference to the following description taken in connection with the accompanying drawing, in which the single figure shows an illustrative embodiment of the invention.

Referring now to the drawing there is shown generally at IS a saturable reactor having saturating leg Illa, and saturable legs Inband Ic. Saturating windings I2 and I4 are received on leg Ia and saturable winding I has two like portions one on leg Ib and the other on leg Ic.

The winding I2 receives a signal or time-varying current by reason of the series circuit de- Cil 2 ned by unidirectional voltage source I8, photocell 2D and winding l2. Thus the saturating leg Ida carries the current or signal to be amplified.

The photo-cell 2i) may be any one of various types vsuch as, for example, a gas, vacuum or multiplier tube or a lead sulde cell. It is eX- posed to. illumination of intensity varying slowly with time, thus causing current flow through winding I 2 varying in like manner with time.

If desired, a photo-voltaic cell may be used to energize winding l2. In this case no battery I 3 is required.

The winding i6 is in circuit relationship with inductor 22 and resistances 24 and 25 to denne a bridge circuit having one set of opposed terminals 23 and 3G and another set of

opposed terminals

32 and 34.

Alternating voltage is applied across the

opposed bridge terminals

32 and 34 by the transformer '3B which is energized by alternating voltage source 33. l

Output voltage from the bridge is taken across terminals 28 and 35. For this purpose the primary winding 38o of transformer 38 is connected directly across these terminals. This transformer has two secondary windings, 38e and 38o, the former acting as an output winding and the latter as a feedback winding.

The feedback winding 38o is connected to the input set of opposed terminals 4ta and 45D of bridge rectifier 4o. The output set of opposed terminals lilo and dtd is connected through variable resistance 42 to the saturating winding I4. Thus the winding i4 is energized in response to the voltage induced in winding 38e.

The rectifier 49 and winding I4 are poled to cause winding I4 to act as a negative feedback winding to oppose the action of winding I2. That is, when current flow through winding I2 increases, the unbalance of the bridge and the resultant change in output voltage of rectifier fil), causes current flow through winding I4 in direction to oppose the magnetomotive force or saturating effect of winding i2 giving rise to that current.

Preferably the bridge constants are chosen to achieve balance when no current flows in winding I2.

If desired, the winding I4 may be poled to aid rather than oppose winding I2. In this Case the sensitivity of the amplifier is increased but the stability and speed of response are reduced.

The output winding 38h is connected to the

voltage dividing resistors

44, 46, and 48, the latter resistance comprising a switch 48a selectably connectable to resistances 43h, 48C or 48d. The com-mon connection of

resistors

48 and 46 is connected to the control electrode of electron tube 5D. The opposite end of resistor 48 is connected to the cathode of tu-be 5U through resistors 52 and 54.

Adjustment of resistance 48 varies the scale range of the instrument E0.

Unidirectional cathode-anode space path voltage is applied to the electron tube 5@ by unidirectional voltage source 56 and resistance 58 which are in series circuit relation across this path.

Meter 60 is an alternating current ammeter responsive to the effective value of the alternating current and is connected in series with the capacitor 62 and resistance 64 between the anode of tube 5E and the resistance 52.

Condenser 62 blocks D.C. current ow through meter 8B. y

It will be observed that source 5S is connected to the junction of resistors 52 and 54. This provides stabilizing negative feedback for amplifier tube 50 and thus causes the deection of meter 60 to correspond more exactly with the value of the induced voltage in winding 3819.

' The saturable reactor lil defines an inductance of value determined by the net magnetomotive force exerted on leg Iiia by the windings i2 and i4. When this magnetom-otive force increases= the legs lb and itc saturate and inductance of coil i6 is reduced. Current loW in coil I6 does not influence windings l2 and I4 because the uX associated with this coil is confined to legs IUD and Ic and the connecting portions of the core I0.

It will be observed that in the mechanism of the present invention we have provided a simple and reliable device capable of amplifying the very low power level and very slow current changes in photo-cell 2d to produce a usable indication on meter 66. rl'his is accomplished in a, highly stable and sensitive manner and, moreover, does not require either a D.C. amplier or a chopper.

While we have shown the amplifier of the present invention adapted to actuate meter 60, it will be evident that it may be used for other purposes as well. It may, for example, actuate a resetting mechanism operable to rebalance the bridge or form part of a closed cycle control system operable to maintain a constant illumination on the photoelectric cell 2D. rIhese, and many other uses will be apparent to one skilled in the art.

While we have shown a specific embodiment of our invention it will, of course, be understood that we do not wish to be limited thereto since many modifications and alternative constructions may be made Without departing from the spirit and scope thereof. We therefore claim by the appended claims to cover all such modifications and alternative constructions as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. An amplier adapted to respond to a slowly varying current from a low energy level source without reacting thereon comprising in combination, a saturable reactor having a saturating leg and a saturable leg, a winding on the saturating leg adapted to carry said current, a winding on the saturable leg, means defining a bridge circuit incorporating said last winding, means to apply alternating potential across one set of opposed terminals of said bridge circuit, an output transformer having a primary winding and a secondary winding, means connecting the primary winding across the other set of opposed terminals of the bridge circuit, a rectier connected across the secondary winding, a second winding on the saturating leg of the saturable reactor, and means connecting the output terminals of the rectier to said last winding.

2. An amplifier adapted to respond to a slowly varying current from a low energy level source without reacting thereon comprising in combination, g, saturable reactor having a saturating legr and a saturable leg, a winding on the saturating leg adapted to carry said current, a winding on the saturable leg, means defining a bridge circuit incorporating said last winding, means to apply alternating potential across one set of opposed terminals of the 4bridge circuit, an output transformer having a primary winding and a pair of secondary windings, means connecting the primary winding across the other set of opposed terminals of the bridge circuit, a rectier connected across one secondary winding, a second winding on the saturating leg of the saturable reactor, means connecting the output terminals of the last winding to the rectifier, and means responsive to the alternating E. M. F. in the other secondary winding to indicate the value of said current.

PAUL T. SEMM. ROBERT T. NAKASONE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS