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Publication numberUS2181728 A
Publication typeGrant
Publication dateNov 28, 1939
Filing dateJul 24, 1936
Priority dateJul 24, 1936
Publication numberUS 2181728 A, US 2181728A, US-A-2181728, US2181728 A, US2181728A
InventorsGreentree Charles D
Original AssigneeGen Electric
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Traffic analyzer
US 2181728 A
Abstract  available in
Images(1)
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Claims  available in
Description  (OCR text may contain errors)

Nov. 28, 1939. C, D. GREENTREE 2,181,728

TRAFFIC ANALYZER Filed July 24, 1936 Fig. Z.

Inventor: Charles D.-Gv`eer1tr-ee,

is Ati-,omweg Patented Nov. 2s, 1939 UNITED STATES TRAFFIC ANALYZER Charles D. Greentree,

Schenectady, N. Y., as-

signor to General Electric Company, a corporation of New York Application July 24, 1936, Serial No. 92,456

6 Claims.

My invention relates to traic counters and analyzers and concerns particularly recorders and registers for selectively showing traflic density according to speeds of vehicles and according to time of day.

It is an object of my invention to provide relatively light and compact but accurate apparatus adapted to be carried about and set up temporarily at various positions on the highways for making traic surveys.

It is also an object of my invention to provide apparatus for selectively counting moving Vobjects in general and for counting pedestrian traiiic.

Other and further objects and advantages of my invention will become apparent as the description proceeds.

In carrying cut my invention in its preferred form, a pair of road contact strips are stretched across a lane or road in which it is desired to count or analyze traic. These contact strips are so combined with a condenser, a source of current, and electric valves that charging of the condenser starts when a vehicle, or a unit of traic to be counted, crosses the first contact strip and charging of the condenser stops when the vehicle crosses the second contact strip. A group of counters is arranged to respond selectively according to the voltage acquired by the condenser in order to count separately the vehicles traveling at speeds below each of several different maximum speeds, and the arrangement is such that the condenser is discharged after the passage of each vehicle. A recorder tape mechanism is also provided which has a marker operated simultaneously with the counters in order to produce a record of the passage of each vehicle distinguishable according to its speed.

The invention will be understood more readily from the following detailed description when considered in connection with the accompanying drawing and those features of my invention which are believed to be novel and patentable will be pointed out in the claims appended hereto. In the drawing, Fig. l is a schematic diagram of a simple traffic-counting arrangement; Fig. 2 is a view partly in cross section of a road contact strip used in the arrangement of Fig. 1; Fig. 3 is an electric circuit diagram of a modification of the arrangement of Fig. 1 for counting vehicles selectively according to speed; Fig. 4 is a 'schematic diagram in perspective of part of the apparatus of Fig. 3, the diagram being drawn to show particularly the arrangement for producing tape records of trailic classiiied according to speed and time of day, and the electrical circuits and circuit elements being omitted; Fig. 5 is a representation of a portion ofa record which might be produced by the apparatus of Fig. 4; Fig. 6 is a sectional view of a contact mat particularly useful for counting pedestrian traiiic; Fig. '7 is a schematic diagram of an arrangement intended primarily for counting pedestrian traffic; and Fig. 8 is a fragmentary representation of a partial modication in Fig. 3. Like reference characters are utilized in the drawing to designate like parts throughout.

Referring now more in detail to the drawing, in the elementary form of the apparatus shown in Fig.' l, a road contact strip II is stretched across a roadway I2 or across a traino lane in an unobtrusive manner in order that automobilists will be unaware of the strip II and will drive their cars over the strip II without change in speed. A source of current I 3 and a counting register I4 with an operating winding I5 are provided. The contact strip II, the current source I3, and the winding I5 are connected together in a series circuit adapted to be completed momentarily by the passage of a vehicle wheel over the contact II. In order to have the traffic count in terms of four-wheel or two-axle vehicles, the register I4 may have dials which advance one digit with two operations of the' mechanism by the winding I5. Trucks with semit-railers thus count as three axles or one and one-half ordinary vehicles. A modified arrangement for producing only one operation upon the passage of a two or three-axle vehicle will also be described hereinafter (page 4, column 1, line 37 et seq.)

In order to make the contact strip I I light and portable for use at different locations and still unobtrusive, it may be constructed as shown in Fig. 2 of two ilexible metallic plates IE embedded in a hollow tape of flexible insulating material, such as rubber, normally spacing the plates I 6 but permitting them to come in contact under the weight of a vehicle when a wheel passes over the contact strip. Preferably, the rubber or compound I'I is of the same color as the pavement across which the contact strip is stretched or the outside of the strip is suitably painted to blend with the roadway and avoid the attention of vehicle drivers. If it is desired to count only those vehicles traveling in a particular lane of a wide roadway or if it is desired to count only the vehicles traveling in one direction on a two-way road, the contact strips II are arranged to have one or both of the metallic plates I6 removed from the portion of the strip Il covering the traillc lanes in which no traffic is to be counted or, if desired, the portion of one or both the metallic plates I6 covering such traffic lanes are cut separate from the portions of the plates IG covering the part of the roadway in which traiic is to be counted. Suitable leads I8 are, of course, brought out from the contact plates I6 or the used portion thereof for connection to the remainder of the apparatus.

In the arrangement'of Fig. 3, there are one or more counting registers, such as I4a, |4b, and I4c, each responsive only to vehicles traveling below a predetermined maximum speed, different for each register or counter. This selectivity is obtained by providing a condenser I9 and two road contact strips IIa and lib with suitable relay means for starting the charging of the condenser I9 when a vehicle crosses the contacts Ila and for discharging the condenser I9' after the vehicle crosses the contacts IIb, the direction of travel of the vehicle being as shown by the arrow from Ila toward lib. There is interposed in the charging circuit of the condenser i3 an electric valve 2D having an anode 2|, a cathode 22, and a control electrode 23. For :tiring the electric valve 20 and starting the condenser charging when a vehicle crosses the strip I la, the contacts of the strip are connected between the control electrode 23 and an intermediate positive potential tap 24 of the charging current source I3. A negative bias voltage source 25 in series with a current-limiting resistor 26 may be connected between the cathode 22 and the control electrode 23 for maintaining the valve 23 normally non-conductive.

.Electric valves 21a, 2lb, and 2lc are connected series with the operating windings 950 Mib, and ic, respectively, of the registers ida, i417,

and Mc in parallel circuits energized by the cur-,

rent source I3. The valves 23a, 2lb, and 21e include anodes 2id, 2Ib, and 2lc,cathodes 22a,-

iib, and 22e, and control electrodes or control grids 28a, 28h, and 28e, respectively, and a grid bias arrangement is provided consisting o a current source 29 and a potentiometer 33 connected thereto with adjustable taps Bla, 3Ib, and 3io connected to the control grids 28a, 28h, and 28o, respectively. llihe contacts oi the road strip lib are connected between the positive terminal 32 oi the potentiometer 30 and the positive terminal 33 of the condenser i@ in order that passage oi a vehicle across the strip lib will raise the grid potentials of valves Ela, 2lb, and 21e the amount corresponding to the charge acquired by the condenser i3 during the passage of a vehicle between the strips ila and lili. For stabilizing the tubes tia, 3117, and Z'lc, a resistor 32 of high resistance, e. g., two or three megohms is conl nected between the cathode and grid of the tube 21a.

The positions of the potentiometer taps Sla, Sib, and 3io are so chosen that the grid biases are such that the valves trip only-if the vehicle speed is below the predetermined values correspending to the voltages for which the taps are set. For example, if the counter I 4a. is intended to count all vehicles traveling below seventy miles per hour, the tap 3Ia is set suiliciently close to the positive terminal 32 of the potentiometer that the charge acquired by the condenser i9 during the passage of the vehicle between strips IIa and IIb will raise the potential of grid 28a enough to iire the valve 27a and cause current to ow through the winding Ia, operating the register I4@ when a wheel ci the vehicle to be counted crosses the strip IIb and closes its contacts.

The faster a vehicle is traveling, the shorter the charging time of the condenser I9 and vice versa. Accordingly, ifv the registers I4b and I4c are to count only vehicles traveling below fty miles per hour and below thirty miles per hour, respectively, for example, the taps 3Ib and 3Ie will be set at correspondingly more negative points in the potentiometer 30 in order that greater condenser charges will be necessary to iire the valves 2lb and 21e for operating the registers I4b and I4c, respectively.

Preferably, the valves 20', 21a, 2lb, and 21e are of the gas or vapor filled or ionic discharge type in which a discharge, once started by a positive voltage on 'the control electrode, continues regardless of control electrode voltage as long as suilicient voltage of the right polarity exists between the anode and cathode.

A relay is provided for breaking the charging circuit to the valve 20, for opening the anode circuits of the valves 21a, 2lb, and 27e, and for discharging the condenser I9 when the vehicle has passed the second contact strip IIb. The relay has its operating winding connected in series with the valve 21a controlling the high-speed register. Such a relay and the high-speed register I4a may have the operating winding I5a in common, as well as the armature 34. The movable armature 34 carries a movable contact 35, and there are provided a pair of normally closed stationary contacts 36 and a pair of normally open stationary contacts 3l adapted to cooperate with the movable contact 35. The contacts 3l are connected across the condenser I9, and the contacts 36 are interposed in series with the current source i3 and the condenser I8 in the anode circuit of the valve 20.

The armatures of the register-operating windings !50., 55h, and l5c also carry suitable projections or striking members, such as collars 38a,

33h, and 380, (shown in Fig. 4) for operating a rocker arm 33 carrying a suitable marking element, such as a pen lili, cooperating with a record tape 4I for producing records of. the passage of the vehicles. The collars 38a, 38h, and 38e are in diierent relativepositions with respect to the armatures. The spindle 42 of the high-speed register Illa carries a worm wheel 43 driving a gear A#I4 attached to the spool 45 on to which the record tape is wound.

For producing a record on the tape 4I of the passage oi time, a suitable time-marking mechanisrn is provided. Such a mechanism may comprise a clockwork 46, a ratchet 4'! driven thereby, and a lever 48 having a spur or lateral arm d@ and carrying a marking device, such as a pen 5ft, cooperating with. the record tape 4I. The teeth or" the ratchet 4l engage the spur 49 to oscillate the lever 48, thereby producing a serrated line 5l in which each serration represents a given interval of time, for example, an hour.

The apparatus operates in the following manner:

When a vehicle approaches the contact strips IIa and IIb, the front wheels rst cross the strip IIa and close its contacts, impressing a positive voltage on the control grid 23 of the valve 2U, causing this valve to become conductive, and a charge begins to flow into the condenser I9. The charging circuit is from the positive terminal of the current source I3, through -the contacts 35 and 36, the conductors 52 and 53, the resistor 54, the condenser I9. and the valve 20, back to the negative terminal o! the source I3. After a given interval, depending upon the speed of the vehicle, the front wheels cross the strip I Ib and close its contacts, impressing the voltage acquired by the condenser I9 upon the terminal 32 of the potentiometer 30, thus raising the potentials of, the control grids 23a, 2lb, and 23c a corresponding amount., If the speed of the vehicle is under seventy miles per hour, the valve 21a is caused to become conductve. 'I'he other valves 21h and 21e may also be caused to become conductive if the speed of the vehicle is suiliciently low. When the valve 21a becomes conductive, a circuit ls formed from the positive terminal of the source I3 through the contacts 35 and 35, the conductor 52. the relay and counter winding I5a, the conductor 55, the valve 21a, and the conductor 56, back to the negative terminal of the source I3. In a similar manner, when the valves 2lb and 21e become conductive, circuits are formed through the winding I5b and I5c, respectively.

When'the valve 21a becomes conductive, the winding I5a, picking up the armature 34, advances the mechanism I4a an amount corresponding to one-half digit. At the same time, the collar 38a (Fig. 4) strikes the rocker arm 39 and causes a short line 51 to be produced upon the record tape 4I, as illustrated at the left-hand end of the sample shown in Fig. 5F. Likewise, register spindle 42 rotates and advances the record tape 4I a short distance, for example, 1/100 of an inch, so that on` the next operation a second line may be produced close to the first line 51. When the annature 34 picks up, it also breaks the condenser-charging circuit at the contacts 36 and it short-circuits the condenser through the contacts 31. Although the closing of the contacts 31 is only momentary, the time of closure is of suilicient duration to discharge the condenser I9 and prepare for a second charging cycle when the contacts IIa are again closed. A compression spring 58 biases the movable contact 35 to the position shown, closing the contacts 36. Similar compression springs return the armatures I5b and I5c to their downward positions. When the contacts 36 are opened by the relay 34 the discharge through the valve 20 is terminated and this valve remains non-conducting until the contact strips I Ia are closed again. v

When the rear wheels of the vehicle cross the contact strips I Ia and I Ib, the operation just described is repeated and the register I4a is advanced another one-half digit so that both axles of the vehicle advance the register I4a a whole digit. In case the speed of the vehicle falls within the proper range, one or more of the remaining registers, such as registers I4b and Hc, are also advanced.

For the sake of clarity, the dimensions along the direction of vehicle travel and the spacing of the road contact strips 'I Ia and IIb are exaggerated in the drawing in relation to the width of the roadway I2. In order to count the axles of vehicles separately, the strips IIa and Il-b are preferably spaced about four feet or close enough for the front wheels to cross both contact strips and produce a complete operation of the apparatus before the rear wheels reach the first strip IIa and far enough apart to obtain an adequate time interval between contact closings of strips I Ia and I Ib for the fastest vehicle.

Referring to Fig. 5, since the serrations of the line 5I each represent a time interval of one hour, one may observe how many vehicles pass within a given hour by measuring the length of the serration corresponding to that hour. It will be understood that the time at which the apparatus is placed in operation is to be written on the record tape 4I in order that the time of day represented'by any portion of the tape 4I may be ascertained by counting the serrations that occur thereon from the end of the tape.

For the sake of explanation, it is assumed that all the vehicles are passing at a speed of seventy miles per hour or less so that all vehicles will be counted by the register`|4a and a pair of vertical lines will be produced for each two-axle vehicle. The collar 38h operated by the winding I5b is mounted closer to the rocker arm 39 than the collar 38a so that, when a. vehicle passes at less than fifty miles an hour and the winding I5b is energized, the rocker arm 39 moves further and produces a longer line, as shown at 59 in Fig. 5,

' representing the passage of a vehicle travelling at less than fifty miles an hour and more than thirty miles an hour. Similarly, the collar 38e is mounted still closer to the rocker arm 39 so that a still longer line is produced on the record tape, as shown at 60 in Fig. 5, representing passage of vehicles at 30 miles an hour or less. In the case of vehicles traveling at lower speeds, the collars on higher-speed armatures have no effect. The passage of each axle produces only one line on the record tape 4I but the speeds of the vehicles may be distinguished by the lengths of the lin s produced. It willvbe apparent that, by examination of the record tape, one can readily ascertain not only how many vehicles have passed during a given time interval but also at what speeds the vehicles passed and how many passed at each speed. The apparatus is thus responsive to the rate of passage of vehicles measured either in miles per hour or vehicles per hour and responds selectively to the rate of passage of vehicles measured in miles per hour.

For cases where several vehicles might run abreast on a wide road and for counting pedestrian traffic, I prefer to employ an arrangement such as that shown in Fig. 'I in which a contact grid or mat 65 is laid across the roadway or sidewalk 66 and a polarizing register 51 is employed. The construction of the mat 65 is shown in detail in the cross-sectional View of Fig. 6 in which the vertical dimension is exaggerated for the sake of clarity.

The resistance mat 65 consists of two separate groups of resistance wires 63 and 69 which may be formed into grids by being joined by cross wires 10 and 1 I respectively. The upper group of wires 68 is normally out of contact with the lower group of wires 69 so that, when a vehicle or a pedestrian treads upon. the rnat 65, some of the wires come in contact and a resistance of a pedetermined value is shunted across a resistor 12 to produce a resultant resistance in series with the current source I3 and the counter operating winding I5, which draws a current sufficient to cause the winding I5 to attract the armature 34. TheV register 61 is provided with two ratchet wheels 13 and 14 geared together and mechanically connected to the register spindle 42. The armature 34 is provided with oppositely pointing detents 15 and 16 and the ratchet wheels 13 and 14 have their teeth arranged in opposite manner so as to cooperate with the detents 15 and 1B, respectively. The dials of register B1 are so arranged that, when a pedestrian steps upon the mat 65 and decreases the resistance in the circuit of the winding l5 a predetermined amount,

the armature 34 is moved a predetermined distance against the force of the tension spring 11 and the dials are moved one-half digit. When the pedestrian steps oif the mat again, the winding I5 releases the armature 34, which is drawn back by the spring 11, and the detent 16 engages the ratchet Wheel 14 to cause the dial of the register 61 to move another one-half digit.

On the other hand, if a second pedestrian steps upon the mat 65 before the rst pedestrian steps off, a second contact is made between the upper and lower sets of Wires 68 and 69 and resistance in the circuit of the winding I5 is reduced still further so as to move the armature 34 an additional step and 'to cause further rotation` of the dials of the register 61. As the pedestrians step off the mat 65, the resistance thereof again increases in steps and the armature 34 is released to complete the registration of the register 61. In a similar manner, if a great number of pedestrians step upon the mat at the same time, the armature moves still further and an appropriate registration is obtained, the spindle 42 being rotated an amount corresponding to one-half digit each time the resistance in the circuit of the winding I5 is increased or decreased. Although the same principle may be employed for counting either Wheeled vehicles or pedestrians, it will be understood that it may be desirable to vary the strength and size of the mat 65 according to the type of service intended. The verbl "tread is utilized in the description and claims to refer either to the action of persons and animals in stepping on the mat 65 or of wheeled vehicles in rolling on to the mat 65.

It may, in some cases, be desirable to reduce the Wear and tear in the mechanism of Figs. 3 and 4 by reducing the number of impulses and counter operations to one for each vehicle passing instead of onefor each axle. This may be accomplished, for example, by interposing a normally-closed switch 18 in one of the leads 19 to the contact strip I Ia, and inserting the operating winding of the switch 18 in the discharge circuit of the condenser I9. The winding 88 is connected to the terminals 8| of a switch 82, which is kept open when it is desired to operate the apparatus with only one impulse for each vehicle.

. The switch 18 is of the quick-opening slowclosing type well known in the art. Various types of such switches or relays are known but, in the type illustrated, there is a short-circuited portion in the winding or a separate secondary coil 83 tending to hold the switch open and delaying its closing. The switch 18 is so adjusted that it does not reclose until the passing vehicle has crossed the strip IIa and, consequently, the rear axle of the vehicle has no eifect on the apparatus. A consideration of the circuit will make it evident that the time delay of closing of the switch 18 adjusts itself automatically to the speed of the vehicle. In case the vehicle passes slowly and a large charge is collected in the condenser I9, there is a large current impulse in the winding 88 when the contactsV 31 close to discharge the condenser I9 throughl the Winding 80 in response to operation of the road strips I Ib. The large current impulse in the Winding 88 induces a large current in the short-circuited coil 83 and holds the switch 18 open for a relatively long period. On the other hand, if the vehicle passes quickly, only a small charge is accumulated and the contacts 18 are held open only a relatit ely short time.

For the sake of illustration, I have referred particularly to the use of a condenser I9 lo perform the timing function and to produce a voltage variation depending on the time required for a traflic unit to traverse the distance between the contact strips IIa and IIb. -It will be understood, however, that my invention 'is not l inductance is the mirror image of a capacitance,

I connect the lead 84 from the contact strip IIb to the negative side instead of the positive side of the inductance I9', i. e., to the terminal 85 instead of the terminal 33 in the particular circuit illustrated in the drawing. Likewise, I place the current-limiting resistor 54 on the negative side of the inductance I9 as illustrated in Fig. 8;

The operation will then be as follows:

When a trailic unit crosses' the strip IIa and fires the tube 20current starts owing in the inductance I9. The inductance opposes the current ilow and sets up a back voltage, tending to hold down the potential of the terminal 85. As time passes, the current increases and its rate of change decreases so that the back voltage oi' the inductance I 9 diminishes, permitting the potential of the terminal 85 to rise progressively. When the traffic unit crosses the contact strip II b, the terminals 85 and 32 are connected together and, of course, the potentials impressed upon the grids 28a, 28h, and 28e depend upon the speed of the traiilc unit which has passed. Operation of the counters and recording mechanism accordingly takes place in the manner already described.

The time relay feature, including the switch 18 for preventing the rear axles of vehicles from affecting the apparatus, may also be employed when the inductance I9 is substituted for the condenser I9. When the inductance I9 is employed, the arrangement of the contacts 36 and 31 is preferably such that the contacts 31 begin to close before the contacts 36 have opened in order to avoid arcing at the contacts 38, which breaking current in an inductive circuit would tend to cause. The inductance I9' tends to maintain the current flow andproduces a iiow of current through the shunt circuit including the contacts 31, the switch terminals 8|, and the winding 80. 'I'he current is greater the greater the time required for the vehicle to transverse the distance between the contact strips 'I Ia and IIb and, accordingly, the time delay with which the switch 18 recloses varies with the slowness of the vehicle which has passed.

I have herein shown'and particularly described certain embodiments of my invention and certain methods of operation embraced therein for the purpose of explaining its principle and showing its application but it will be obvious to those skilled in the art that many modifications and variations are possible and I aim, therefore, to

For example, an incover all such modifications and variations as fall 75 within the scope of my invention which is deiined in the appended claims.

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

1. A trailc analyzer comprising in combination, a p rst circuit closer adapted to operate when a traflic unit crosses a given point, a second circuit closer adapted to operate when the traiiic unit crosses a second more advanced point, a condenser, a source of charging current, an electric valve of the ionic discharge type with an anode, a cathode, and a control elecrode, said condenser and said anode and cathode being connected in series to said current source to form an anode circuit, said rst circuit closer being connected in a grid circuit to said cathode and said control electrode, a second electric valve with an anode, a cathode and a control electrode, a relay with normally open contacts, normally closed contacts, and an operating Winding, said winding being connected in series with said normally closed contacts and the anode and cathode of said second electric valve to said current source, said normally open contacts being across said condenser, a source of biasing voltage connected in series with said second circuit closer, said condenser and said iirst valve between the cathode and control electrode of said second electric valve, and a counter connected in responsive relation to said relay.

2. A traiiic analyzer comprising in combination, a rst circuit closer adapted to operate when a trafc unit crosses a given point, a second circuit closer adapted to operate when a tramo unit crosses a second point, a condenser, a source of condenser-charging current, an electric valve with an anode, a cathode, and a control electrode, said condenser and said anode and cathode being connected in series to said current source to form an anode circuit, said iirst circuit closer being connected in a control electrode circuit to said cathode and said control electrode, voltage-responsive means, and relay means, the latter having normally closed contacts interposed in said anode circuit, normally open contacts across said condenser, and a control winding adapted to be energized by said voltage-responsive means, said second circuit closer having contacts in series with said condenser and said voltage-responsive means.

3. A trailic analyzer comprising in combination, a condenser, a source of charging current, means for starting charging of said condenser when a traffic unit crosses a predetermined point, an electric valve having a control grid circuit with a predetermined negative bias, a counter, normally inoperative means for applying the accumulated voltage of said condenser in said control grid circuit when the tralc unit crosses a second more advanced point, and means interposed in series with said electric valve and said current source for operating said counter and disconnecting said condenser from the charging source in response to a discharge through the electric valve.

4. A traillc analyzer comprising in combination, an electric circuit element offering an opposition to the flow of electric current, which opposition Varies with the flow of current during the continuance thereof so as to produce a varying voltage in said element, a source of current, means for starting ilow of current from said source into said electric circuit element when a trafilc unit crosses a predetermined point, an electric valve having a control-grid circuit with a predetermined negative bias, normally inoperative means for subjecting said control-grid circuit to the variation in voltage in said electric circuit element when the traiic unit crosses a second more advanced point, and current responsive means interposed in series with said electric valve and said current source for disconnecting said condenser from the charging source in response to a discharge through the electric valve.

5. A traic analyzer comprising in combination, a condenser, a source of charging current, means for starting charging of said condenser when a traiiic unit crosses a given point, a plurality of electric valves with control grids and cathodes, a grid-biasing potentiometer with points at different relative potentials to which said control grids are connected, means for connecting said condenser between the cathodes of said electric valves and a terminal of said potentiometer when the traic unit crosses a second more advanced point, and a plurality of counters with operating windings, each in series with one of said electric valves and said current source.

6. A tramo analyzer comprising in combination, a condenser, a source oi charging current, means for starting charging of said condenser when a traliic unit crosses a given point, a biasing potentiometer, a plurality of electric valves with control electrodes and cathodes, each of said control electrodes being connected to a diierent point on said potentiometer, means for connecting said condenser between the cathodes of said valves and a point on said potentiometer when a tramo unit crosses a second given point, and a plurality of current-responsive devices each in series with one of said electric valves and said current source.

CHARLES D. GREEN'I'REE.

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Classifications
U.S. Classification377/9, 361/187, 340/936, 346/40, 340/670, 200/86.00R, 346/114, 346/113, 324/180, 235/99.00A, 346/33.00D, 340/934, 346/30, 361/170, 346/49
International ClassificationG08G1/01
Cooperative ClassificationG08G1/0104
European ClassificationG08G1/01B