US2423480A - Multiple recording instrument - Google Patents

Description

July 8, 1947. J. A. CALDWELL MULTIPLE RECORDING INSTRUMENT Filed June 20, 1942 10 Sheets-Sheet 1 FIG.

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JOHN A. CALDWELL LINE ATTORNEY.

y 1947- J. A. CALDWELL 2,423,480

MULTIPLE RECORDING INSTRUMENT Filed June 20, 1942 10 Sheets-Sheet 2 INVENTOR. JOHN A. CALDWELL ATTORNEY.

FIG. 2.

y 1947- J. A. CALDWELL MULTIPLE RECORDING INSTRUMENT Filed June 20, 1942 10' Sheets-Sheet s INVENTOR. JOHN A. CALDWELL BY 5 M ATTORNEY.

July 8, 1947- J. A. CALDWELL MULTIPLE RECORDING INSTRUMENT Filed June 20, 1942 1O Sheets-Sheet 4 ill llFllP 3 --7l pp.

INVENTOR. JOHN A. CALDWELL BY W TORNEY.

y 1947- J. A. CALDWELL 2,423,480

MULTIPLE RECORDING INSTRUMENT Filed June 20, 1942 1,0 Sheets-Sheet 5 INVENT OR. JOHN A. CALDWELL BY Q TORNEY.

y 1947- J. A. CALDWELL 2,423,480

I MULTIPLE RECORDING INSTRUMENT Filed June 20, 1942 10 Sheets-Sheet 6 INVENTOR. JOHN A. CALDWELL FIG. l4.

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July 8, 1947.

J. A. CALDWELL MULTIPLE RECORDING INSTRUMENT 10 Sheets-Sheet 7 Filed June v20, 1942 FIG. [2A.

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10 Sheets-Sheet 8 J. A. CALDWELL MULTIPLE RECORDING INSTRUMENT F iled June 20, 1942 w w. wvwgllllkt i l j n 4 a 4 d v I a I v I 1 I 1 I 1 v i L U 4 July 8, 1947.

INVENTOR. JOHN A. CALDWELL lwm HWM IH F L U T s j L H IUHHHHHIFFML TORNEY.

INVENTOR.

mama! .1. A. CALDWELL MULTIPLE RECORDING INSTRUMENT Filed June 20, 1942 July 8, 1947.

JOHN A. CALDWELL BY 5% FIG. 24.

MULTIPLE RECORDING INSTRUMENT Fi led June 20, 1942 10 Sheets-Sheet 10 i l l 'n m y ""1 IN V EN TOR- (355 354 39 JOHN A. CALDWELL ATTORNEY.

Patented July 8, 1947 UNITED STATES PATENT. OFFICE MULTIPLE RECORDING INSTRUMENT John. A. Caldwell; Philadelphia, Pa, assignor to The Brownlnstrument Company; Philadelphia, Pa., a corporation of Pennsylvania Application June 20,1942, Serial No. 447,863

exhibiting element, and in somecases to operate a control. Each ofthese instruments must in herently move the exhibiting element in a series of steps until it is properly positioned. Thereafter, it the instrument is a multiple recorder, som means is used tomove the-marking element into engagement withv the chart and" to subsequently connect the instrument to another con dition, tobe measured and recorded.

With few exceptions, a multiple IGCOI'diIlg instrument is made to measure and record each condition within given periods of time.

together a recording operation can not occur until after the given,- period of time ha expired, even though the instrument almost immediately positions the marker. In another type of recording, instrument, a record. of the value of the condi tionis made apredetermined number of cycles after the marker is properly positioned. Both types of. instruments require an excessive period of. time after the marker is properly positioned;

before the recording operation cantake place.

It is an, object of myinvention to provide a; multiple potentiometer instrument which is not cyclic in operation so that the marker may be continuously and rapidly moved to recording position. It is" a. further object of the invention, to provide means to make the record of thevalue of the, condition substantially immediately after Ifthe conditions being measured have their values close immediately after the instrument reaches a balanced condition to actuate the printing mechanism. This. detecting mechanism is quiet in operation as well as being positive in the performanceof its functions. g

It is a further object of the invention toprovide a recording instrument in which the. chart is easily accessible for inspection and may be readily and quickly changed when anew. chart is needed. The chart supply and rewind mechanism is also. supplied with novel adjusting means to compensate for irregularly wound'rolls or chart paper.

It is a further object of the invention to provide a multiple potentiometer havin only two contin uously driven parts. These. parts are. the above mentioned detecting and chart drivin mechanisms. The other movi g. parts of the instrument operate only when a condition change is. occurring and when a record is made of the same. It is a further object of the invention, toprovide a. multiple potentiometer instrument in, which the various parts are so positioned relative to each other that a. compact, readily accessible instrument is provided. The parts are so placed that adjustments and repairs, when, necessary, may be made easily and in a minimum of time. The arrangement is such that the casing is no larger than that used for the ordinary potentiometer.

'The various features of novelty which. characterize my invention are pointed out with. particularity in the claims annexed to and formin a part of thi specification. For a better understanding of the invention, however, its. advantages and. specific objects obtained with its. use,

reference should be had to the accompanying drawings and. descriptive. matter in which I have illustrated and described a preferred embodiment of the invention.

In the drawings-.-..

Figure; l is a schematic; diagram of the potentiometer circuit and instrument,

Figure 2. is. a. front View of the instrument in it casing with certain portionsbroken away;

Figure 3 isa top view. of the instrumenttaken on line 3--3 of Figure 2,

Figure 4 i a detail of the slide-wire adjusting means,

Figure 5 is a section taken on line 5-5 of Figure 4,

Figure 5A is a view of a portion of the frame looking from, the right in Figure 3,

Figure 6 is a front view of the instrument casing with the recordin mechanism. removed,

Figure 7 is a view, partly in section, of the cold junction compensating resistor,

Figure 8 is a back view of the supporting frame for the recording mechanism, with certain portions broken away,

Figure 9 is a section taken on line 9-9 of Figure 8,

Figure 16 is a sectional view showing a chuck for supporting one end of both the chart supply roll and chart take-up roll,

Figure 11 is a sectional View showing a supporting chuck for the other end of the supply roll,

Figure 12 is an outside view of the left-hand side of the frame of the instrument with associated parts mounted thereon,

Figure 12A is a section view of a pulley moun E.

Figure 13 is an enlarged view of a driving pawl,

Figure 14 is a view taken from the top of Figure 13,

Figure 15 is a view of a modified form of detector cam,

Figure 16 is a view of another modified form of detecting cam,

Figure 17 is a view of a portion of the inside of the left-hand side of the instrument frame.

Figure 18 is an inverted view taken on line I8l8 of Figure 12 and a direct view taken on line l8l8 of Figure 17,

Figure 19 is a side view of the print wheel carriage looking from the right in Figure 2,

Figure 20 is a sectional view of a portion of the print wheel carriage,

Figure 21 is a view taken on line 2l--2l of Figure 19,

Figure 22 is a view taken on line 2222 of Figure 21,

Figure 23 is a view taken on line 23-23 of Figure 19,

Figure 24 is a side view of a modified form of chart drive mechanism,

Figure 25 is a view taken on line 25-25 on Figure 24,

Figure 26 is a view of a modified form of a slidewire assembly,

Figure 27 is a bottom view of the Figure 26,

Figure 28 is a view taken on line 28-28 of Figure 26,

Figure 29 is a view taken on line 29-29 on Figure 26,

Figure 30 is a view taken on line 30-40 on Figure 26,

Figure 31 is a view of a modified form of drive crank, and

Figure 32 is a view looking from the right at Figure 31.

Referring first to Figure 1, there is shown schematically a wiring diagram of a potentiometer of the self-balancing type which may be used to indicate, record, and/or control the value of a condition being measured. For purposes of this description it may be assumed that the conditions being measured are temperatures. For this purpose there are shown four thermocouples T, although any other desired number may be used.

The thermocouple T which is responsive to the temperature that is to be measured, operates in conjunction with a potentiometer network which is generally designated at l to form a self-balancing potentiometer system. Upon a change in temperature to which the thermocouple is subjected an unbalanced D. C. current in one direction or the opposite is produced depending upon the direction of unbalance of the potentiometer system. This D. C. current is supplied to an amplifier unit 2 having a vibrator or equivalent device designated at 3 and a transformer designated at 4 which are connected to an amplifying circuit that is not shown. The vibrator 3 preferably is of the form disclosed and claimed in the co-pending application of Frederick W. Side, bearing Serial Number 421,176.

The direct current supplied to the amplifier is converted by the vibrator to a pulsating current of one phase or of an opposite phase depending upon the sense of unbalance of the potentiometer system. This pulsating current is detected by the transformer 4 and is amplified by a vacuum tube system which may take the form of that shown in the copending application of Walter P. Wills filed December 1, 1941, and having Serial No. 421,173. The current from the amplifier is used for operating a reversible motor generally designated at 5 in one direction or the opposite direction. This motor serves to operate a slide wire assembly to rebalanoe the potentiometer system and also serves to move an indicating and recording mechanism which will be described in detail below.

The potentiometer network may comprise three resistances, 6, 1, and 8 which are connected in series. These resistances are usually formed of some wire having substantially no temperattue resistance coeflicient and may be used for calibration purposes. Connected in parallel to these resistances are a battery 9 which may be in the form of a dry cell and a dual vernier rheostat comprising resistances l0 and II and electrically connected sliding contacts 12 and I3 which engage with the resistances I0 and II respectively. The rheostat may be operated by any suitable type of knob, there being a direct mechanical connection between the knob and the contact l2 and a lost motion connection between the knob and the contact I 3. Upon initial movement of the knob, the contact I2 is first moved and then the contact [3 is moved thereby providing a vernier adjustment. The battery 9 and the rheostat are connected in series with respect to each other and in parallel with the resistances 6, T, and 8. Also connected in parallel with the first mentioned resistances are two other resistances l4 and I5, which are in turn connected in series with each other. The resistance M is preferably made of copper or other material having a suitable tcmperature resistance coeflicient and the resistance I 5 may be made of manganin having substantially no temperature coeflicient of resistance. The resistance 1 4 operates to compensate for temperature changes at the cold junction of the thermocouple and is so connected into the network that the voltage drop across it is added to the thermocouple E. M. F. The resistance I5 is utilized primarily for standardization purposes and has a resistance value such that the voltage drop across it is equal to the voltage produced by the standard cell.

The slidewire assembly consists preferably of a coil l6 which is wound around and insulated from a core 11. Cooperating with the slide wire is a collector'bar l3 which is also wrapped around a core l9. The slide wire and the collector bar are electrically connected by a sliding contact 20 that is driven by the motor 5 to rebalance the potentiometer circuit. The terminals of the slide wire I6 and its core I! are connected in parallel around the resistance 7.

A two position switch 2| is connected into thev potentiometer network and serves the purpose of performing two functions; namely, for :c'onnecting the potentiometer .circuit for normal operation (run) and forstandardizing the potentiometer system (standardizing). :Schematically, this switchmay comprise a plurality of. switch armsof which arms 22 and '23 "are moved together by means 'ofaknob 24. 'Switcharm'22 carries on it a contact 25 and the switch '23 carries on'it a contact 26,'which contacts are adapted to engage respectively contacts 21 and 28 that are carried by otherarmsin'the switch assembly. The contact 28 is-connected with one lead from one of the thermocouples T. This lead is shown as including a'wire '29 which terminates in a cold lunction 38 that is located closely adjacent toiresistance I4. Connected to the junction 30 is a 'resistance 3I which hasa condenser 32in parallel with it and a wire 33 that leads to the switch con tact 28. The other thermocouple lead runs directly through wire 34 to a second cold junction 35, which is also located adjacent resistor I4 -and from there through a wire '36 to the collector core IS.

The switch 2I i shown in the run position. When the switch is in its standardizingposition the contact 25 engages a contact 31 and the-contact 26 engagesacontact 38.

schematically shown as forming a portion of the amplifier 2 is the transformer 4. This transformer comprises a primary winding 39 which has a center tap 39'. Primary winding .39 is wound around a core structure 4I that also has on it a secondary winding 42 that isconnected with the amplifier. A shield is provided between the primary and secondary windings and all of these parts may be cased in a suitablehousing.

Also shown in a schematic manner is vibrato-r 3 which comprises a vibrating reed 43 that normally engages contact 44 and 45 but which during its vibration will separate first from contact 44 and then from contact 45. The reed is vibrated under the influence of a Winding 46 that is connected to a suitable source of alternating current. A permanent magnet 41 is associated with the reed and is used for polarization and synchronizing. This structure is also enclosedin a suitable housing. One end of the primary winding 39 of the transformer is connected by a wire to the contact 45 of the vibrator, while the other end of the primar winding is connected by a wire 50 to the contact 44. The center tap 39' of the primary winding is connected by means of a Wire 48 with the contacts 25 and 26 so that it can b connected into the potentiometer circuit. Vibrating reed 43 is connected by means of Wires 48 and 49 with the potentiometer circuit between resistances I4 and I5. The effect is that a circuit is completed through the thermocouple, the vibrator and the transformer to the potentiometer circuit, and in effect, the vibrator and transformer serve substantially the same function as a galvanometer in an ordinary potentiometer circuit.

From time to tim it becomes necessary to standardize the potentiometer and readjust the contacts I 2 and I3 to compensate for the decrease of the voltage of battery 9. To this end a standard cell 52 is connected into the potentiometer circuit by means of a wire 53 that connects this cell with contact 31. When the switch '24 is in its lower or standardizing position, the standard cell is connected through the transformer and vibrator by means of the wires 48', 48, and 49 so that "it is placed in parallel around resistance I5. The same movement of the switch'24 brings contacts 26 and 38 intoengagement to connect conductors 48 and 54. This places a resistance 55 in shunt around the vibrator and transformer.

.In the operation of the potentiometer system the battery 9 places a potential drop across the slide wire I6 a portion of which, depending upon the position of contact 20, is opposed by the thermocouple voltage. When the potentiometer is in balance no current is flowing through the thermocouple circuit, but if the temperature which is being measured by the thermocouple then connected in circuit changes, the thermocouple voltage will change and current will flow in one direction or the other through the potentiometer circuit to set up an alternating potential in the secondary winding 42 which is in phase or out of phase with the alternatingsupply voltage. This alternating potential is amplified and used to control the operation of the motor 5 in the proper direction to move contact 28 to rebalance the potentiometer circuit. If, for example, the temperature should increase, the thermocouple T then in circuit would produce an increased E. M. F. and cause a current flow through the potentiometer circuit. This current flow will go through wire 29, cold junction 30, resistance 3|, wire 33, contacts 28, 26, and wire 48 to the center tap 39 of the transformer winding 39. From here the current will flow either through the upper or the lower half of this winding, depending whether the contact 45 or 44 is then engaging the reed 43 and through Wires 48 and 49 to the potentiometer circuit. This produces an alternating potential in the transformer secondary 42 of one phase with respect to the supply that is amplified by the amplifier to control the operation of the motor 5 in the proper direction to rebalance the potentiometer circuit. If the temperature had decreased, current would flow in the opposite direction or through wires 49 and 48 to the vibrator 3 and from the transformer through wire 46 creating an alternating potential in the transformer winding 42 of the opposite phase with respect to the supply which is amplified to control the operation of the motor 5 in the opposite direction. It will be noticed that the motor 5, as illustrated, is a rotating field motor that has a squirrel cage rotor with interconnecting bars. Two of the opposite fields of the motor, the power windings, are connected across the supply lines 62 with a condenser 56 in one of the leads. The other opposite fields of the motor, the control windings, are connected to the output of the amplifier 2, and have a condenser '51 in parallel with them. Each pair of the motor field is connected in series. When the voltage and current through the motor control windings lag the voltage and current in thepower windings the motor will rotate in one direction. When the voltage and current in the control windings lead those in the power windings, the motor will rotate in the opposite direction. The-amplifier shifts the phase of the current of the motor control winding so that the motor will rotate in the proper direction. As the motor rotates it drives a pinion 258 integral therewith that engages a gear 58.

Attached to. movable with the gear 58 is a pulley 59 around which is wrapped an endless cable 653 connected. to contact 2! so that as the motor rotates, the contact will be moved in one direction or the other to rebalance the potentiometer circuit in a manner above described. One end of the cable 68 runs over a pulley 45 that is carried by an arm I58 pivotally mounted at I51 and biased by a spring I52 to take up the slack in the cable. The other end of the cable runs around a pulley 148 which has frictionally attached to it a detector member This detector member is used in conjunction with other parts to be later described to detect balance of the potentiometer or non-movement of the cable, to actuate the marking mechanism that records the value of the temperature being measured and to simultaneously connect the instrument to another thermocouple.

The amplifier 2 is connected to the line by suitable leads which are shown at 62, and may be disconnected from the line by a double pole switch 63. There is also disclosed a chart driving motor 64 which may be a rotating field motor of the same type as the motor 5. This motor also has two of its fields connected directly to the leads 62 and the other two connected to these leads by a switch 65. With this arrangement the chart motor 64 may be deenergized while the potentiometer system is still energized, but the motor is always stopped when the potentiometer is deenergized.

All of the instrument mechanism, including the parts which have been described above are located within a casing 66 that may be a casting or sheet metal as desired. This casin has provisions on it whereby it can be mounted in an instrument panel or it may be mounted against a wall. Such provisions are old in the art, and their details are not pertinent to the present disclosure. The casing is provided with a door 6'! (Fig. 3) which is hinged at 68 to its right-hand side. This door is provided with a knob 59 that serves to control a latch (not shown) and may have in it a look so that the instrument may be closed against unauthorized tampering. The door has a window it in it through which a chart, a scale and an indicating pointer may be seen.

Located within the casing are various of the parts which have been described. For example. in Figure 6 there is shown a view of the casing 66 with the potentiometer mechanism removed. It will be seen that the amplifier 2, having the vibrator 3 and the transformer 4, is mounted in the casing on the right-hand side against the rear wall. The battery 9 is mounted against the back wall as is the standard cell 52. Suitable terminal blocks for the various connections within the instrument itself and to the thermocouples are also mounted on the back wall of the casing.

A swinging frame 12 is hinged at H to the left-hand side of the casing. This frame is mounted so that it can be swung completel out of the casing but may be locked into position in the casing by means of a latch '13 of the type shown in Williams Patent 2,283,304. issued May 19, 1942, which cooperates with a latch plate 74 attached to the right-hand side of the casing. This latch is actuated by a knob 15. The frame carries on it supporting members for all of the resistors that have been described above, as well as the chart, the printing mechanism, the detecting mechanism and the switches for the chart driving motor and the current supply to the amplifier. The frame '12, as shown in Figure 3, is formed with a pair of mechanism supporting ends and a connecting part, that also has various parts mounted upon it. For convenience in the following description, the left end of frame [2 in Figure 3 will be referred to as 12A while the right end will be referred to as HR. The connecting part will continue to be referred to by the numeral 12.

On the upper front part of the frame 72 is a small sheet metal casing 16 that extends across the width of the instrument. This casing has in it supports 11 for various of the resistors as best shown in Figure 2. Each of these supports is attached to a plate 18 that may be bodily removed along with the resistors if it is desired to change the range of the instrument. In such case all of the resistors are removed as a unit, and a new set of resistors is placed in the casing. Also mounted in the casing 16 on the lefthand end thereof (Figure 3) is the cold junction resistor I4 that is placed in a separate box I 4A (Figure 7) along with the cold junctions 38 and 35. The sheet metal casing 16 is pivoted at 19 on the frame portions 12A and 12B so that it may be swung up for inspection and cleaning of the slide wire 16 and collector 18 which are attached to the bottom thereof. The casing is maintained in its normal position by a spring plunger 83 which is mounted in the frame 12A and cooperates with a small indentation on the left face of the casing. The right-hand end of the casing receives a threaded shaft 8| having a milled head SEA which has a conical face on it. When the casing is in operative position the shaft 8| lies, as shown in Figure 5A, in a groove 32 in the frame portion 72B.

Attached to the bottom of the casing i5 is .a plate member 83 made of some insulating material to which are fastened the slide wire [8 and the collector 58. These parts, as best shown in Figure 3, are not mounted on the member 83 so that they are parallel to its sides, but are mounted at a slight diagonal. This is done so that as the contact 29 moves along the slide wire and collector there will be a slight wiping action which will tend to clean the slide wire and at the same time will cause the contact to wear evenly rather than form a groove in its surface.

In originally calibrating the instrument it is desirable to be able to shift the slide wire relative to the contact carried by the print wheel carriage in order to adjust the zero of the instrument. To this end the insulating plate 83 is so mounted that it can be shifted e W Se re ative to the bottom of the casing 16. For this purpose the casing is provided with a tongue 84 that is punched upwardly from its bottom plate 85 as best shown in Figure 5. A screw 86 is rotatably mounted on the tongue 84 and has below the tongue 2, disk 81 to which is attached an eccentric pin 88. This pin extends into a groove 89 that is cut into the insulating plate 83 and extends across the latter. In order to adjust the plate which carries the slide wire relative to the casing 15, the screw 85 is rotated to move the pin 88. As the pin, which bears in the groove 89, is shifted lengthwise, the slide wire assembly will be moved relative to the casing '15. The entire slide wire assembly and the casing 16 are rigidly fastened in place on the frame 123 by the means of the screw 8!. When for example. the casing 16 has been lifted upwardly around its pivots T9 for some purpose. such as cleaning the slide wire, it may be returned exactly to its original position by means of the screw 8!. The conical head of the screw 8i cooperates with' the groove 82 in the frame to pull the entire assembly tightly against the frame 12B to locate the same in some given position.

In order to shift the contact 20 along the slide wire IE to rebalance the potentiometer in response to an unbalance thereof produced by a change in temperature of one of the thermocouples, the contact 20 is held in engagement with the slidewir and the collector bar and is mounted on a print wheel carriage 90. This print wheel carriage has extending from its upper rear face a clamp plate 9| in which the ends of the cable 80 are clamped. Therefore, as the motor 5 rotates, the print wh'eel carriage will be moved back and forth across the instrument and carry the contact 20 with it across the slide Wire to a position of balance. This print wheel carriage has on it a print wheel 92 that is provided with printing characters or numerals 93 which are to be moved into engagement with the chart when the print wheel carriage reaches a balanced position. The manner in which the print wheel carriag operates will now be described.

Refer now to Figures 19 to 23 which show the print wheel carriag in detail. The print wheel carriage 90 is supported at its front end by a roller 94 that is received in a channel member 95 which runs the length of the instrument, and is attached at its ends to the frame members 12A and 12B. The rear end of the print wheel carriage is supported by means of rollers 96, 91, and 98 which bear against and roll on a shaft 99 that is also attached to the frame parts 12A and 123 at its ends. The rollers 96 and are rigidly mounted on the print wheel carriage, and the roller 98 is supported on a spring I00 which is attached to the print wheel carriage. In this manner, the roller 98 is forced into engagement with the rod 99 to prevent any upward movement be tween the print wheel carriage and the shaft, and to keep the print wheel carriage rigidly mounted in position as it moves back and forth across the chart 2 I9. upon which the recording of the temperature is to be made. The print Wheel carriage 90 has formed on one sid thereof, a downwardly extending plate IOI which has a stud shaft I02 rigidly mounted therein. Pivoted on this shaft is a supporting plate member I03 that has a roller I04 journaled on its rear end. This roller rides in a channel member I05 that is moved in a manner to be described later, for the purpose of producing the printing operation, and for the purpose of actuating a switch to connect the instrument to different thermocouples.

As more particularly shown in Figure 21, the shaft I02 has a sleeve I06 rotatably mounted on it. This sleeve, along with a second sleeve I08, that is rotatable on the first, is held in position on the shaft I02 by means of a suitable lock washer I01. The plate I03 is staked to the sleeve I08 so that the plate and sleeve can oscillate around the shaft. The sleeve I08 has a gear I09 and a ratchet wheel I I0 staked to it. Theratche't wheel serves the purpose of rotating the sleeve I08 on the sleeve I06 to rotate the print wheel and an ink pad assembly which is mounted on th former sleeve. The ink pad assembly is made of a tubular moulding II I that may be of plastic or metal and which is formed with a series of radially extending fin's IIIA that serve to divide this moulding into a series of compartments. The axial bore of the moulding has a circular flange with a sloping face or surface H2, formed on its right-hand side, which engages with'a cooperating surface H3 on a flange member '4 that is suitably fastened to the sleeve I08. This member is provided with a pin I I5 that cooperates with a groove I I6 formed in a central opening III in the flange of the moulding III. The central opening II'I of the flange is eccentric in shape as shown best in Figure 22. The ink pad assembly is held on sleeve I00 by means of a knob I I8 that has a cam face I I9 engaging the left end of the moulding and which serves to properly center the assembly. Located within the radially extending compartments of the moulding i I are felt pads I20, each of which may be impregnated with a different color ink if desired, so that each of the records made of the different thermocouple temperatures will be recorded in a distinctiv-e color. The felt pads are held in place in the moulding by means of a shield I2I as best shown in Figure 21.

The ink pad assemby is mounted on the pen carriage by moving the moulding III containing the pads onthe sleeve I08 from the left in Figure 21. Since the printing characters 93 normally engage the ink pads I20 some means must be provided for keeping these parts separated whil the ink pads ar being moved into place. This is the reason why the central opening I I! is made eccentric in shape. In mounting the moulding on the sleeve I08, the moulding is first rotated until its groove I I6 is lined up with pin I I5, and moved toward the right in Figure 21. The moulding is then moved clockwise from the axial position in Figure'22 around pin I I5 as a center (counter-clockwise in Figur 19') to separate the felts I20 and the printing characters 03. Thereafter the moulding is again moved to the right in Figure 21 until its surface II2 engages surface II3. Knob H8 is then screwed into place; engagement between its surface H9 forcing surfaces H2 and H3 into engagement with each other. Thus the moulding is rotated back into an axial position and centered by the concentric surfaces II 3 and HQ with the ink pads in engagement with the printing characters on the print Wheel.

Also mounted on the plate I03 is a stud shaft I22. This shaft has rotating upon it, a sleeve I 23 that is held in place by means of a washer E24. Staked to the sleeve is a drive gear I25. Also mounted on the sleeve I23 is the print wheel 92 that is held in proper position relative to the sleeve by means of engagement between a slot in the print wheel, and a pin I26 extending from the sleeve. Before the print wheel is placed on the sleeve, an indicating disc I2! is moved into place as shown best in Figure 23. This disc has a series of numbers on it which correspond to the print characters 93 on the print Wheel, and are so displaced with respect to these characters, that when a printing character is in engagement with the chart, the corresponding numeral on this disc will be in a position where it can be seen from the front of the instrument as shown best in Figure 2. A pointer I28 is attached to the plate I03, and cooperates with the disc I21 to indicate the proper number. The print wheel and the indicating disc are held in place on the sleeve I 23 by means of a knob I229 that is screwed on the outer end of the sleeve. As best shown in Figure 20, the gear I09 serves to drive the gear I25 by means of idler pinions I30, both of which are mounted for rotation on the plate I03.

Since it is imperative that the print wheel be exactly located with respect to the print wheel carriage a spring -I3I is placed between the plate IOI of the print wheel carriage and the oscillating plate I03. This spring serves to take up any slack in the parts, and always keeps the plate I03 properly placed, with respect to the plate IOI.

11 For a similar reason, a spring I32 is inserted between the plate I03 and the gear I in order that the print wheel will be properly located on its shaft I22.

The print wheel carriage 80 is also provided on its front end, with an indictaing pointer I34 that cooperates with a scale I35, which is attached to the channel member 95 and extends across the front of the instrument. This indicator serves the purpose of showing the value of the temperature being measured as it is moved in front of the scale I35.

The print wheel and the ink pads are normally kept from rotating on their shafts by means of a pawl I36 that is pivoted at I31 on the plate I03, and which is biased into engagement with teeth on the ratchet wheel II8 by means of a Spring I38. A roller I39 which extends from the pawl I36 engages a surface I40 on a second pawl I4! that is pivoted at I42 on the plate IIII. This pawl MI is normally biased in a counter-clockwise direction in Figure 20, by means of a spring I43 that is equal in strength to the spring I38. This latter pawl is used to rotate the print wheel to bring a new printing character into printing position above the chart each time a new thermocouple is connected to the instrument. The operation takes place due to an oscillation of plate I03 which is imparted thereto by means of the channel member I05. This channel member is moved in an arc concentric with the stud shaft I02, by means of a mechanism to be described, after the instrument has reached a balanced position.

Cable 60 which is used for driving the print wheel carriage passes over four pulleys I45, I45, I47, and I48, and over the drive pulley 59 that is operated by the shaft of motor 5. This drive pulley will be described more in detail below. Pulley I45 is rotatably mounted on a stud I 49 which projects upwardly from the arm I 50. The arm I50 is pivoted at vI 5I and is biased by a spring I52 in a direction to take up all slack in the cable. The pulley I46 is rotatably mounted on a stud I53 which is carried by a boss that is formed in the frame I2, as best shown in Figure 8. The pulley I41 is rotatably mounted on a stud I54 which is mounted at its upper end in the frame 12 located at a point to the right of pulley 59 in Figure 8.

The pulley I48 over which the cable 60 also passes is attached to a bushing MBA that is journaled in a bearing I48B which is fastened to the frame 12A, as best shown in Figure 12A, The bearing is provided with a sleeve I480 which receives the bushing. As has been previously stated the instrument is provided with a detecting mechanism which operates to detect when the instrument comes into balance, and in response to such balanced position to operate a printing mechanism and connect the instrument to another thermocouple. It will be remembered that a detecting plate 6| is moved by the cable 60 to give an indication when the cable has stopped moving and the printing carriage is properly positioned. This is done by frictionally mounting the plate 6I on the bushing I48A. To this end the plate 6| is frictionally received between a flange I56 formed as part of the bushing 8A and a washer I51 which is rotatable with the bushing but may move axially thereof. Extending through the bushing is a bolt I which has between its head and the washer .I5'I a second washer I55A. The latter washer is drawn into engagement with the former by a spring I58 that is compressed between the upper end of bushing MBA and a nut I553 The amount of friction between the plate BI and the parts I56 and I5! may be adjusted by varying the tension of the spring I58. A second nut is placed on the end of bolt I55 beyond nut I55B to lock the latter in place.

As the plate 6| is rotated along with the pulley I48 when the instrument is in its unbalanced condition, this plate is periodically brought back to a neutral position by a cam I59 which is driven at a constant speed by the motor 64, and which cam is mounted to rotate with its driving gear I590 on a hollow shaft I59D that is attached to and eXtends from the side of frame 12A (see Figure 18). The cam I59 is a three lobe cam and it has three high points I60 which periodically pass through a V-shaped groove I6I that is formed in the plate 6I. One side of this groove is extended to form a tongue I62 on the end of the plate 6|. The cam I59 is provided with three pawls I63 which are pivoted at I64. These pawls can move between the position shown in Figures 12 and 13, and the dotted line position of Figure 13 and are held in either position by engagement between the following end of the pawl and a spring I65 which is mounted on the cam. The movement of the pawls is limited by a pin I93 on each pawl which extends through an opening I94 in the cam. Each pawl is formed with a single projection I66 midway between its edges on its leading end, and with two projections I6! adjacent the edges of the pawl on its following end. The terms leading and following refer to the direction of travel of the pawl with the cam I59, the latter rotating in a clockwise direction in Figure 12.

In the operation of the instrument, the cam I 59 is rotated at a constant speed. Assuming that the instrument is in an unbalanced position and that the print wheel carriage is being moved in one direction or the other, this means that the plate 6| will be rotated so that the edges of the slot will bear against one side or the other of the cam. This plate is periodically brought into a neutral position as a point I60 of the cam passes through the apex of the slot I6I. If the instrument is still unbalanced, the plate 6| will have been moved either clockwise or counterclockwise in Figure 18, so that the tongue I52 will be out of the path of the projection I66 and will be in the path of one of the projections I61 by the time the pawl reaches the tongue. This will continue until such time as the instrument reaches balance, when the plate 6| will remain in its neutral position after it has been moved there by the cam. The tongue I52 will then be in the path of the projection I66 on the next pawl I63 which moves past this tongue. Consequently the tongue will then engage the projection I66 and move the pawl clockwise in Figures 12 and 13 to the dotted line position of the latter figure.

When the pawl is moved in its clockwise direction a cut-out portion I68 of the pawl will be moved radially inward of the cam until it is in the path of a pin I69 that projects from one arm of the crank I10 attached to a shaft III journalled in the hollow shaft around I59D which the cam I59 rotates. Normally durlng the time that the instrument is unbalanced, the inner surface of the pawls are at a radially greater distance from the shaft I'II than the pin I69, but when the instrument reaches balance, the next pawl passing the plate BI is flipped so that its 13 lower end moves inwardly to bring it into engagement with the pin I69. The crank I10 is thereupon rotated to perform the operation of printing and connecting the instrument to another thermocouple.

The outer end of the crank is provided with a roller I12 that moves in a slot I13 which is formed in the end of a lever I14. This lever is provided with a bushing I89 that rotates on a shaft I15 whichis attached to and extends from the frame 12A. A second lever I16 is rotatable on the bushing I89, and has its outer end fastened to the channel member I to move the latter. It might be noted at this point that the other end of the channel I 05 may well be fastened to a second lever, not shown, of the same length as lever I16 which second lever is pivoted at a point coaxial with the shaft I15 and on the frame 12B sothat the two levers and the channel I05 will form a yoke that will move as a rigid member. The lever I16 is moved by the lever I14 to actuate the print mechanism by means of a spring I19. which has one end attached to each lever. The angular position between the two leversmay be adjusted by means of an adjustment screw I11.which is fastened to an inwardly bent tongue I 90 on the lever I14 and engages an abutment I18 on the lever I16.

The crank I16 is shown in Figure 12 at its rest position. When one of the pawls is flipped to a driving position and the crank is rotated, the first action of the latter is to move the levers I14 and, I16 in a clockwise direction as the crank moves past point I80 in the cam slot. This movement serves to bring a printing character on the print wheel 92 into engagement with a chart passing over the chart drum I44. If the printing character engages the chart before the roller I12 has reached the point I 80 of the cam slot the spring I19 will give to permit overtravel of the lever I14. Continued rotation of the crank will first move the lever I14.and the parts connected to it in, a counter-clockwise direction and then in a clockwise direction until such time as the roller I12 again reaches the position shown in Figure 12.

As the crank Irotates, it will be subjected to varying loads depending on whether it is moving the lever I14 in one direction or the other. In order to smooth out the load on this crank, the shaft I1I is provided with a disc I9I (Figure 17) to which'a cam I8I is adjustably attached by means of screws I92. This cam is engaged by a roller I82 that is mounted on the end of a lever I83. The lever I83 is pivoted at I84 and is biased to bring the roller I82 into engagement with the surface of the cam by a fairly stiif spring I85. As shown in Figure 17, the cam and roller are in relative positions that will be assumed when the crank I10 is at rest as shown in Figure 12. It will be noticed that the roller I82 is resting in a low spot I86 on the surface of the cam to definitely locate the crank I 10 with respect to the cam slot I13. As the crank starts to rotate, cam I8I will be rotated about half-way to the high point I 81 as roller I12 reaches point I86 of the slot I13. Thereafter, the cam surface continues to rise during the time that the lever I14 is being moved in a counter-clockwise direction. Such operation serves to put a load on spring I85 to retard the action of crank I10 and prevent it from running ahead of its driving pawl. When the crank has reached such a rotative position that it starts to move lever I14 clockwise in Figure 12, the cam I8I hasreached a position where its radius begins to decrease so that the force of spring I gives a slight camming action to the shaft I1I tohelp bring the crank I10 smoothly to its rest position.

By the time crank I10 has completed itsrevolution the instrument will have been connected to another thermocouple and will have begun to rebalance itself. If the instrument has not come to balance again the tongue I62 will engage one of the projections I61 of the driving pawl to move that pawl counter-clockwise on its pivot I64 and shift portion I68 radially outward beyond the pin I69. Crank I 10 will then remain at rest until such time as the tongue I62 is centered and engages the projection I66 on another pawl, If, however, the instrument has rebalanced itself prior to the time crank I10 completes a revolution the tongue I62 will be centered and the driving pawl will not be moved out of driving engagement with pin I69, As a result the crank will continue its rotation and immediately proceed with another printing operation.

It is noted that a stop I88 is provided beneath the part 6! to back up this part, and prevent its being bent, if for some reason the cam should exert an unduly large force downwardly on this part.

The three lobe cam disclosed in Figure 12 makes an instrument that is practically instantaneous in printing after the instrument has come to balance. In some cases it may be desirable to have a slightly longer delay between the time that the instrument comes to balance and a printing operation takes place. In such a case a two-lobe cam as shown in Figure 15 at I59A or a single lobe cam as shown in Figure 16 at I59B may be used. It is also noted that the speed of rotation of the cam I59 may be changed to accomplish the samepurpose. By designing the instrument with a cam with the proper number of lobes and the proper speed of rotation, almost any speed of operation can be obtained. Generally speaking, however, the speed of rotation of the cam is correlated with the speed and operating characteristics of the balancing motor 5.

It may be that the print wheel carriage has practically moved into printing position and can be moved the remainder of the distance between the time one of the points I60 of the cam I59 has centered member 6| and the time that projection I66 of the next pawl passes the tongue I62. If this is the case the tongue I62 will have moved slightly out of neutral, but not far enough to be in the path of a projection I61. A printing operation will therefore occur. It is possible for the instrument to be almost balanced, but not quite close enough for the above operation to take place. If this is the case tongue I62 may first engage projection I66 and then projection I61 to first throw the pawl into and then out of driving position before its out out portion I68 has traveled far enough to engage pin I69. Moving the pawls forwardly or backwardon the cam I59 relative to points I60, and varying the distance between projections I61 as well as the width of tongue I62 will have an effect on the amount of movement of the print wheel carriage that will be permitted after the member 6| has been moved to its neutral position. As an example, if the cam I59 is rotating at a speed of one revolution every three seconds, printing operations can occur at a minimum-of once every three seconds. If a three lobe cam is used a printing operation will take place within a maximum time of one second after the instrument has balanced out and may occur in a shorter time if the instrument is almost balanced when the member 8I is moved to its neutral position. The maximum time that will occur between any two printing operations is equal to the time it takes the print wheel carriage to move from its old to its new position plus one second. This time, therefore depends upon the speed of motor '5.

By using various combinations of cam speeds and pen carriage speeds almost any desired speed of operation of the recording mechanism may be obtained as shown by the table below. In the table the cam speed is in seconds per revolution; the carriage speed is in seconds for the print wheel carriage to move from one end to the other of its path of travel; and of chart is the percent of full scale travel which can be covered by the print wheel carriage during the minimum time between two consecutive recording operations. For example, if a two lobe cam is used and is rotating at a speed of 6 seconds and the carriage has a speed of 11 seconds for full scale, a printin operation will occur every six seconds if the consecutive records are not more than 43% of the chart width apart. If the records are further than 43% of chart width apart, printing can occur after any three seconds after the instrument comes to balance. Again, if a three lobe cam having a speed of three seconds per revolution is used in an instrument having a carriage speed of 22 seconds, a printing operation will occur every three seconds if the consecutive records are not more than 7.5% of the chart width apart. If the records are further apart than 7.5% of chart the printing can occur within one second after the print wheel carriage is properly positioned.

Cam Cam Carriage Percent of Lobe Speed Speed Chart 1 3 ll 17 l 6 ll 43 1 l 1 l 100 l 3 22 7. 5 l 6 22 17 1 l5 2 50 2 3 ll 17 2 6 ll 43 2 ll 100 2 3 22 7. 5 2 G 22 17 2 15 22 5O 3 3 ll 17 3 6 ll 43 3 15 ll 100 3 3 22 7. 5 3 6 22 17 3 15 22 50 l 3 44 3. 5 l 6 44 7. 5 l 15 44 25 3 l 4 17 3 l /2 5% 17 l 44 l 60 88 50 In the operation of the print wheel, as the channel I05 is moved upwardly, the member I03 will be moved in a counter-clockwise direction in Figure 19 or a clockwise direction in Figure 20 to bring a printing character 93 into engagement with a chart that is placed over a chart driving drum I42.

Due to the shape of the slot I73 in lever I74 the print wheel will be moved slowly into engagement with the chart with sufiioient force to produce pressure printing, rather than hammer printing as is so often the case in multiple recording instruments. Pressing the printing character into engagement with the chart rather than dropping it into engagement therewith produces quieter operation as well as being easier on the various parts. When the print character engages the chart the spring I79 will flex to permit lever I14 to move through its full stroke. Upon continued rotation of shaft I'II the lever I14, as has been described, will be moved downwardly in Figure 12. This means that the member I03 will be moved counter-clockwise in Figure 20 with the pawl I36 in engagement with ratchet H0 thus preventing any relative rotation of the parts mounted on member I03. As this movement continues the roller I39 on pawl I36 will move to the right along the surface I40 until such time as the lever arm between roller I39 and the pivot I42 for pawl I4I has been shortened enough fOr the force of spring I43 to overcome that or spring I38. At that time the pawl I4I will move into engagement with the ratchet I I0 and, acting through the arm I40, will move pawl I36 out of engagement with the ratchet. This will occur at the bottom of the stroke of lever I74, and with the printing wheel in its highest position above the chart drum. Continued rotation of the crank I70 will then begin to move the lever I14 clockwise in Figure 12, which means that member I03 will move clockwise in Figure 20. During this movement the pawl MI is in engagement with the ratchet I10 and will thereby prevent that ratchet and the gear I09 from rotating relative to the part IOI. While the member I03 is moved clockwise, however, idlers I30 and gear I25 upon which the print wheel is mounted will rotate, thereby moving the print wheel clockwise in Figure 20 and counter-clockwise in Figure 19 to bring a new printing character into printing position above the chart drum. As this clockwise movement of the part I03 continues the roller I39 will move away from the pivot point I42 and the lever arm between I39 and I42 will become large enough for spring I38 to overcome the force of spring I43. At this time the pawl I36 will move into engagement with the ratchet I I0 and maintain the parts in the position shown until the next printing operation occurs. It will be seen, therefore, that the ratchet is positively locked for movement with the part I03 by pawl I36 or is positively locked against movement by the pawl I4I. At no time is the ratchet wheel, and therefore the print wheel, free to rotate because the pawls are so designed that pawl MI is moved into engagement with a tooth of the ratchet as pawl I36 is moving out of engagement therewith. It will, therefore, be seen that as the crank I70 starts to rotate after the instrument has come into balance its movement will produce a printing operation and then an operation whereby a new printing character is brought into printing position above the chart.

The same movement of the channel member I that brings the print wheel into engagement with the chart and rotates the print wheel also serves to connect another thermocouple to the instrument. This is done by rotating brushes in a switch into engagement with other contacts of the switch. A switch by means of which this may be accomplished is shown at I55 (Figure 8) in the drawings and may well be of the type described and claimed in Harrison Patent 1,770,918, issued April 22, 1930. Such a switch is provided with a shaft I95 by means of which the brushes may be rotated. As shown herein, the switch is mounted on a bracket I91 that is attached to a portion of the frame 12A.

I of a ratchet 205.

The movement of the channel member I acts to'rotate the shaft I96 by means of a connector I98 (see Figure 17) which is attached to the channel member near one end and which is pivoted to one end of a floating link I99, the other end of which is pivoted to one arm of a lever 200. This latter lever is mounted for rotation around a shaft 20I and has mounted on its other arm a pawl 202 that is pivoted at 203 on the lever. Pawl 202 is biased by means of a spring 204 in a direction which will bring its end into engagement with one or the other of the teeth Movement of the lever 220 is used to rotate the ratchet and a bevel gear 206 that is attached thereto, both of them being mounted on the shaft 20I. The pawl 202 is provided with a roller 201 that is adapted to move along a surface 208 formed on one arm of another pawl 209 that is pivoted at 2G0 on a plate 2II. This plate forms part of a bracket 2I2 that serves to support the switch actuating mechanism and the shaft 20I. Pawl 209 is biased in a counterclockwise direction by spring 2I3 which i equal in strength to the spring 224. Beveled gear 209 meshes with a beveled pinion 2I4 that is attached to the upper end of a shaft 2I5 which serves to rotate the switch shaft I96. Shafts 2I5 and I96 are joined together by means of a universal joint which, in this case, comprises a spring metal plate 2I6 that is fastened to the shaft 2I5 at diametrically opposed points 2!! and is fastened to the shaft I96 at point 2I8. The universal joint serves to compensate for any slight misalignment that may appear between shaft 2 I 5 and I96.

On the initial upward movement of the channel member I95 when a printing ope-ration takes place, the pawl 202 will move the ratchet 295 a slight amount in a clockwise direction. This movement is imparted thereto through link I99 and lever 200, and has no effect on the switch except to move its brushes slightly backwards on the contacts. When, however, the channel member I05 starts its downward movement in Figure 17, the lever 200 is moved in a counter-clockwise direction and acts through the pawl 202 to rotate the ratchet 205 also in a counter-clockwise direc tion. This movement i imparted to the gearing and through shaft 255 to switch 95 to connect another thermocouple into the potentiometer circuit, the arrangement being such that the connection is made immediately after the downward movement begins. It will be seen that immediately after the printing operation takes place the switch is adjusted to connect another thermocouple to the instrument. After this operation is performed, the upward movement of the channel I05 is used to reset the pawl and ratchet mechanism of the pen carriage, and the switch adjusting mechanism. While this adjusting movement is taking place, the potentiometer is being rebalanced so that no unnecessary time is lost between printin operations. The ratchet mechanism used for adjusting the switch is similar in operation to that previously described which was used on the print wheel carriage. As the lever 200 moves counter-clockwise, roller 20! will move toward the pivot 2I0 until such time as the leverage between the two pawls changes enough for the force of spring Elli to overcome that of spring 20 4. When this occurs, pawl 202 will be lifted out of engagement with the ratchet, and pawl 209 will move into engagement with the same. This occurs near the bottom of the stroke of lever 200. Thereafter, as lever 200 moves in a clockwise direction, the ratchet wheel 18 will be held from turning by pawl 209 as pawl 202 is moved to a position in which it can engage the next tooth on the ratchet wheel.

The chart, which has been mentioned above, is shown best at 2I9 in Figure 2. It will be seen that the chart is provided with horizontal and vertical lines, and has on one edge a series of round holes 220, and on its opposite edge a series of slots 22!. The horizontal lines on the chart serve the purpose of indicating the time at which some particular record is made, while the vertical lines or calibration marks serve to indicate the value of the temperature that has been recorded. As best seen in Figure 12, the supply roll 222 of the chart is mounted between the frame portions 12A and 1213 near the bottom, and toward the rear of the frame. The chart, when being inserted into the instrument is pulled upwardly, and forwardly over the rod 223. The chart is then threaded toward the rear of the instrument between a guide member 224, and the chart drum I49. This guide member serves to .irect the chart around the drum, from which it is brought down across the front of the instrument, and over a chart backing plate 225 to a chart take up roll 226, which is located at the bottom of the frame directly in front of the sup-ply roll.

The backing plate 225 is preferably hinged at its lower end, as shown at 221, so that it may be moved out of the way when a new chart is to be inserted into the instrument. The backing plate is held in place by means of a pair of lock members 228 that engage cut-out portions 229 on the upper corners of the backing plate.

These locking members are held in engagement with the portions 229 of the backing plate by means of spring members 230 upon which they are mounted.

The supply roll 222 and the take-up roll 220 are mounted at their left ends in Figure 2, or their right ends in Figure 8 in the frame portion 12A, upon a spring mounted chuck 23I shown in Figure 10 which is adapted to be wedged into the end of the core 232 of a supply or take-up roll. Thi chuck is attached to a shaft 233 that is mounted for rotation in a bushing 234 inserted in the frame 12A. The chuck is forced to the left in Figure 10 into engagement with the end of the roll by means of a spring 235, and is limited in its movement bya washer 236 on the outer end of the shaft. It will be noted that the shaft 233 is made of a large diameter near the chuck and a small diameter to the right thereof. This construction gives a large and rigid bearing surface near the end of the chart roll and permits the use of a bushing 234 of the type shown which fully encloses the spring 235.

The left end of the supply roll 222 in Figure 8 or the end in frame portion 123 is mounted on e. non-rotatable chuck 292, shown in Figure 11, that is attached to a shaft 293 which is threaded through the frame 12B. This shaft may be provided with a knob 294 to rotate it and shift the chuck axially. In any event a lock nut 295 is threaded over the shaft and is jammed against the frame to hold the chuck firmly in position when it has been adjusted. Since the chuck 292 is non-rotatable it serves to put a drag on the supply roll to prevent the same from over-running. Both the chuck which supports the left end of the supply roll and that which supports the left end of the take-up roll, to be described below, are axially adjustable so that the rolls may be shifted to the proper position relative to the chart drum 144. The right end of the take-up roll 226 adjacent frame portion 123 is supported by an adjustable and rotatable chuck 231 shown in detail in Figure 8. The chuck is provided with a tongue 238 that is adapted to engage the usual driving notch formed in the end of the roll core (see Figure 2). This tongue extends through an opening in the edge of the chuck and is formed of spring material which always acts to move out into the position shown. When inserting a roll over a chuck of this type, the tongue 238 will be moved against the flange of the chuck. Thereafter, as the roll or the chuck is rotated, the tongue will spring into its driving position as soon as the driving notch of the core is in alignment therewith. The chuck 231 is attached to a shaft 239 whose outer end is provided with a knob 249 whereby the chuck can be rotated at will to supply or take up slack in the chart. The shaft 239 is journaled in a sleeve 241 that is threaded through an opening in the frame 1213. The outer end of this sleeve is provided with a thumb nut 242 whereby the sleeve can be rotated in order to shift the chuck to its proper axial position and is provided with a lock nut 243 that can be jammed against the side of the frame to hold the sleeve in place.

The chuck used for the take-up ro'-l has attached to the shaft 239 a sprocket 244. This sprocket is driven by a chain 245 that extends over a second and larger sprocket 246. An idler sprocket may be used against the chain to take up slack if this is deemed necessary. In order to compensate for increasing diameter of the chart on the take-up drum the sprocket 246 is frictionally driven by the chart drum 144 by means of a. pair of friction washers 241 that are keyed to a shaft 248 on the end of the chart drum. The sprocket and the friction washers are moved together and against a nut 249 that is screwed on the shaft by means of a plate 259 which is forced to the left bv springs 252. Each of the springs 252 surrounds a plunger 25! which is attached to the plate 259 and which is freely movable through openings that are formed in the end of the chart drum. In order to adjust the tension of the springs. and therefore the friction with which the sprocket 246 is driven, the nut 249 may be moved to the left or right along the shaft 248.

The chart drum in this embodiment of the invention is driven at a constant speed by the motor 64 through a. gear train 253 that starts with the pinion 54A (Figures 12 and 18) and ends with the gear 254 that is frictionallv mounted on the drum. It will be seen from Figure 2 that the chart drum is provided on each end with a series of projections 255 that project through the openings 220 and 221 in the chart. By means of these projections and openings the chart is positively moved past the print wheel at some given speed. The speed of the chart drum may of course be changed by substituting a different gear reduction between the motor and the chart drum. The shaft 248 upon which the chart drum is mounted is provided with a knob 256 by means of which the chart drum may be rotated to properly position the chart with respect to the print wheel. There is also provided amember 296 which extends over the edge of the chart and which can be used as a guide to properly set the time lines on the chart relative to the print wheel and a so-called tear-ofi strip 251 which is made of some transparent material and which extends across the shaft by a set-screw 299.

the instrument in front of the chart. The purpose of this member is to act as a straight edge when a piece of th chart is to be removed.

The drive motor 5 which serves to move the print wheel carriage back and forth across the chart is mounted beneath the chart and behind the broken portion of the frame as shown in dotted lines in Figure 8 and in Figure 9. This motor has extending therefrom a shaft upon which is mounted a pinion 258 that meshes with and drives the gear 58 to which is attached the pulley 59 around which cable 60 is wrapped. The gear 58 is made with teeth around most of its peri hery and is provided with a projection 259 either sid of which can jam against the pinion to limit rotation of the gear and therefore travel of the print wheel carriage. Gear 58 and pulley 59 are attached by rivets or other suitable means to a sleeve 26B that is rotatable on a shaft which is suitably attached to and projects from the rear of frame 12. Roller bearings 291 are provided between the sleeve 266 and shaft EM, and the sleeve is held on the shaft by a bolt 298 which is prevented from rotating relative to If it is desired the cable 60 may be attached to the pulley 59 by any suitable means to prevent the possibility of any slippage occurring between the two.

The instrument is also disclosed as being provided with a switch S, shown in Figure 8, that can be used to actuate a signal when some predetermined temperature occurs, or for any desired control purpose. The switch S herein is operated by a cam 262 that is mounted on the sleeve 26B, and held in proper position thereon by spacer members 396 and a thumb nut 361. The cam has a cut out portion 263 that is joined with the surface of the cam by inclined edges 264 and 265. The switch itself is mounted on a plate 256 that is suitably attached to the frame 12. Attached to the plate 266 and insulated therefrom is a piece of material 261 upon which the switch blades are mounted. One blade is shown at 258, and has a contact 269 on its right end. The second blade is numbered 219 and is shown as being pivoted to the member 261 at 21!. This blade has a contact 212 on its right end which is adapted to engage with the contact 269 and is normally held in engagement with this contact by means of a spring 213. Also mounted for rotation around point 21! is a lever 214 which has a roller 215 projecting from it into engagement with the surface of the cam 262.

In the operation of the instrument, it may be assumed that the gear 53 and cam 262 are rotating in a clockwise direction in Figure 8. From the position shown in that figure, the rotation of the cam 262 will move the cut-out portion 263 to the right, and cause roller 2'55 to ride up inclined surface 264 to an idling position on the surface of cam 262 with the contacts 263 and 212 closed. Thereafter upon a reverse movement of the earn 262, or a movement in a counter-clockwise direction, the roller 2% will bear on the e: ge of cam 262 until first the inclined surface 294 and then the cut-out portion 263 comes under the roller, at which time it will return to the position shown in the drawing. Continued rotation o the cam will move the roller 215 up the surface again to the edge of the cam. As this is taking place, th left side of lever 2T4 will move into engagement with the left end of switch. blade 270. and thereby move that blade around its pivot and against the force of spring 273 to separate the switch contacts. Continued rotation of the cam

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