US2716214A - Thermal integrator - Google Patents

Description

Aug. 23, 1955 w. G. WING 2,716,214

THERMAL INTEGRATOR Filed oct. 21, 1952 Myx L O 2 lu E@ 4l 4 7 E Q L) l q IE q Z l' g m .a5 I E [u lg l: l h Q l Y I E l l to 2L,

TMEE-r- ,4 INVENTOR W/L/s C7. l/V/NG ATTORNEY United States IPatent THERMAL rNrEGnAToR Willis G. Wing, Roslyn Heights, N. Y., assigner to Sperry Rand Corporation, a corporation of Delaware Application October 21, 1952, Serial No. 315,885

4 Claims. (Cl. 323-52) This invention relates to integrators, and more par- 1 ticularly, is concerned with a thermal time delay device for securing an approximation to the time integration of limited voltage signals.

Servo mechanisms frequently employ an integrating loop to reduce long term errors in the system. Various integrators have heretofore been proposed having a long time constant. However, for averaging an input signal over periods of 20 seconds or longer, known integrating systems, such as rotary or other mechanical integrators, or resistance-capacitance integrators, frequently prove to be complicated and expensive, or may be prohibitive in size for some applications.

Thermal time delay devices have been used for integrating voltage signals over a long time interval. One such known device employs resistance elements which differentially heat associated coils of high temperature coeicient resistance wire in response to an input signal, The resistance wire coils are in turn connected in a bridge circuit, producing an output signal when the bridge is unbalanced by unequal changes in resistance of the coils with differential heating by the input signal. Thus, when an input signal is applied to a thermal integrator of this type, unequal heating of the coils results in a gradual change in the balance of the output bridge, the initial rate of change being approximately proportional to the magnitude of the input signal.

However, such a known thermal integrating device is subject to the objection that the close proximity between the coils and the resistance elements necessary for good thermal coupling gives rise to substantial capacitive coupling between the input and output circuits when the integrator is used with signal carriers having frequencies of the order of 400 cycles.

It is the general object of this invention to avoid and overcome the foregoing and other difficulties of and objections to prior art practices by the provision of a thermal-type integrating apparatus which is rugged and compact in construction, relatively simple and inexpensive to build, and yet, reliable and foolproof in operation.

Another object of this invention is to provide means for producing an output voltage signal which changes in amplitude at a rate proportional to the amplitude of an input voltage signal over a substantial time interval up to 20 seconds or longer.

Another object of this invention is the provision of a thermal integrator which may be operated on either A.C. or D.-C. input signals.

Another object of this invention is to provide apparatus for producing a time delay by thermal means which is only moderately affected by changes in ambient temperature.

These, and other objects of the invention which will become apparent as the description proceeds, are achieved by the provision of a thermal-type integrator comprising a frame to which a pair of spaced parallel bimetal elements are each secured at one of their respective ends. A spacer bar having low thermal conductivity is secured to and between the opposite ends of the bimetal elements. The bimetal elements are so arranged that they tend to bend toward or away from each other with similar changes in temperature so that only unequal heating and cooling of the bimetal elements results in lateral movement of the spacer bar. Electrical heating means, associated with each of the bimetal elements, dilerentially heat the elements in response to an input signal to the thermal integrator, the unequal heating of the elements effecting a net lateral movement of the spacer bar at a rate determined by the magnitude of the input signal. An E-transformer pick-olf is supported by the frame and connected to the spacer bar in such manner that the movement of the spacer bar with unequal heating of the bimetal elements actuates the pick-off to produce an output signal of amplitude substantially proportional to the deection of the pick-ofi.

For a better understanding of the invention, reference should be had to the accompanying drawing, wherein:

Fig. 1 is a plan View of the thermal integrator showing the electrical connections thereto;

Fig. 2 is a sectional view of the thermal integrator taken substantially on the line lI-ll of Fig. l; and

Fig. 3 is a graphical representation of the output signal of the thermal integrator as a function of time following application of a constant input signal.

With specic reference to the form of the invention as illustrated in the drawing, the numeral 10 indicates generally a base to which is secured by a suitable means, such as screws l2, an angle bracket 14. The angle bracket 14 has secured thereto a spacer bar 16, which is preferably made of a low thermal conductivity material such as stainless steel. The spacer bar 16 is adjustably secured to the angle bracket t4 by means of the screws 18 and 2t) which pass through longitudinal slots 22 and 24 respectively in the spacer bracket 16 and threadedly engage the angle bracket lll. The slots 22 and 24 permit lateral adjustment of the spacer bar 16 relative to the base llt).

Secured to each end of the spacer bar 16 are a pair of bimetal elements 26 and 28 which are of a reverse welded type that bends in an S-shape when heated. Each bimetal element is actually made of two sections of bimetal welded end to end, each section bending the opposite direction from the other with a change in temperature. The bimetal elements are suitably secured to the spacer bar, as by screws 30.

The opposite ends of the bimetal elements are secured to a second spacer bar 34 by suitable means, such as screws 36. The bimetal elements 26 and 28 act as cantilever supports for the spacer bar 34, bending of either of the bimetal elements producing lateral movement of the spacer bar 34.

Wound around each of the bimetal elements 26 and 28 are coils 38 and 40 respectively, the coils being wound with suitable resistance wire so that current passing through the coils generates heat which is transferred to the bimetal elements 26 and 28. Electrical insulation in the form of a coating or sleeving 4l on both the bimetal elements prevents electrical short circuiting between the individual turns of the coils and between the coils and the bimetal elements.

The coils 38 and 40 are electrically connected in series at a common junction 42. The other end of the coil 38 is connected to a reference voltage source supplying a voltage er, while the other end of the coil 4t) is connected to a second reference voltage source supplying a voltage e2. To elect heating of the coils 38 and 40, the reference voltages e1 and e2 may be either alternating current or direct current signals.

If e1 and e2 are alternating current reference signals, they must be of opposite phase and equal amplitude to provide equal heating of the coils 3S and 40 with the common junction 42 being at Zero potential. For example, a suitable source for e1 and e2 would be a centertapped transformer. lf direct current reference Voltage signals are used, they must be of equal potentials and opposite polarities to give equal heating of the coils 33 and 4t) with the common junction 42 at zero potential.

An input signal ein is applied at the common junction 42. lf the input signal is in phase with e1 and out of phase with ez (or of the same polarity as ci and opposite polarity from e2 where direct current signals are used) the coil 4@ is heated more than the coil 3S, resulting in unequal bending stresses in the bimetal elements 26 and 2S and a lateral displacement of the spacer bar 34. The bimetal elements are mounted to act in opposition to each other, so that a net lateral movement of the spacer bar 34 is effected in the direction of bending of the hotter bimetal element.

lf the phase of the input signal is reversed, the coil 3S is heated up more than coil 4t), resulting in a net lateral displacement of the spacer bar 34 in the opposite direction. The extent of the movement of the spacer bar 34 depends on the difference in temperature between the bimetal element 26 and the bimetal element 28.

Referring to Fig. 3, motion of the spacer bar 34 resulting from constant input signals of selected amplitudes are plotted as a function of time. Curve 45 is for a small input signal ein, and curves 47 and 49 are for respectively higher amplitudes of input signals. During the interval t to t1, the slopes of the respective curves are substantially straight and at different slopes which correspond to the different input signals. Thus, over the region to to li, the rate of movement of the spacer bar is substantially constant and varies directly with the magnitude of the input signal. By providing means for detecting movement of the spacer bar, an output signal can be produced which approximates the time integral of the input signal, that is, an output signal which changes at a rate substantially proportional to the instantaneous magnitude of the input signal.

Motion of the spacer bar 34 is preferably detected by means of an E-transformer type pick-ntf, indicated generally at 48. The magnetic circuit of the E-transformer includes three arms t), 52 and 54 joined by a common bar 56. A pair of outer coils 58 and 60 are wound on the arms Sti and 54 and are connected in series at 62. An exciting coil 64, connected across a source of alternating current, is wound around the center arm 52.

The outer arms 5t] and 54 are bridged by a jumper bar 65 which has a projection 66 at the middle thereof forming a magnetic gap 68 with the center arm 52. The whole E-transformer assembly is held together and supported from the bracket 14 by a clamping bar 70 secured in position by bolts 71.

Secured to the spacer bar 34 and passing through the gap 68 is a low resistance shorted turn including a U- shaped copper member 72 and bridging copper bar 74 soldered across the ends of the U-shaped member 72 and extending through the gap 68. When the shorted turn is centered in the gap 68, flux produced by energization of the exciting coil 64 splits and passes equally between the two coils 50 and 52. No net output signal is produced at terminals eout since the coils 5t) and 52 are connected so as to oppose each other. Movement of the spacer bar 34 either to the right or to the left unbalances the flux paths between the two coils 50 and 52, to produce a net output signal whose phase depends upon the direction in which the spacer bar 34 is moved. Strips of iron, indicated at 76, secured along the edges of the bridging bar '7 4, reduces the effective air gap for the portion of the ux that splits around the shorted turn.

By moving a shorted secondary coil rather than an armature, as in the conventional E-transformer, slight transverse movement of the spacer bar 34, which necessarily accompanies the lateral movement thereof, does not affect the balance or sensitivity of the pick-off.

The E-transformer is set to provide Zero output signal with no integrator input signal ein by adjusting the spacer bar 16 so that the shorted turn is positioned in the center of the gap 6E. Since the limited elements oppose each other in bending with changes in temperature, the ambient temperature does not affect the Zero setting, changes in the ambient temperature acting equally on the two elements and thereby being cancelled out.

From the above description, it will be recognized that the various objects of the invention have been achieved with the provision of an integrator which is relatively simple in construction and design. The long time delay between the input and output signals provides an approximate time integration of either A.C. or D.C. input signals and is particularly adapted for use in servomotor control systems where a smoothing effect is required. The sensitivity and gain of the integrator are good, and the construction provides complete isolation between the output and input circuits.

Since many changes could be made in the above construction and many apparently Widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A thermal integrator comprising a frame, a pair of spaced parallel reverse welded bimetal elements, each of the bimetal elements being secured at one end thereof to the frame, a spacer bar having a low coefficient of thermal conductivity secured to and between the opposite ends of the bimetal elements, the bimetal elements being mounted to bend in opposite directions with respect to each other when heated, electrical heating coils extending around each of the bimetal elements and connected in series across a source of potential, the input signal to the integrator being connected to the common junction between the heating coils, an E-transformer supported by the frame and having an air gap in the center leg thereof, and a shorted turn of conductive material supported by the spacer bar and extending through the air gap, the E-transformer producing an output signal in response to changes in position of the shorted turn in the air gap with movement of the spacer bar.

2. A thermal integrator for producing an output signal that is a smoothed version of an input signal of changing amplitude, the integrator comprising a frame, a pair of spaced parallel reverse Welded bimetal elements, each of the bimetal elements being secured at one end thereof to the frame, a spacer bar having a low coecient of thermal conductivity secured to and between the opposite ends of the bimetal elements, the bimetal elements being mounted to bend in opposite directions with respect to each other when heated, electrical heating coils extending around each of the bimetal elements and connected in series across a voltage source, the input signal to the integrator being connected to the common junction between the heating coils, an E-transforrner supported by the frame including an armature connected to the spacer bar, the E-transformer when energized by an A.C. source producing an output signal having an amplitude which is varied in response to changes in position of the spacer bar.

3. A thermal integrator comprising a frame, a pair of `spaced parallel reverse welded type bimetal elements, each or" the bimetal elements being rigidly secured at one end thereof to the frame, a spacer bar having a low coefficient of thermal conductivity rigidly secured to and between the opposite ends of the bimetal elements, the bimetal elements being mounted to bend in opposite directions with respect to each other when heated, electrical heating coils extending around each of the bimetal elements and connected in series across a source of potential, the input signal to the integrator being connected to the common junction between the heating coils, and means supported by the frame and connected to the spacer bar for producing an output signal having an amplitude which is varied n response to changes in position of the spacer bar.

4. A thermal integrator for producing an output signal that is a smoothed version of an input signal of varying amplitude, said integrator comprising a pair of thermomechanical elements adapted to change their physical dimensions when heated, first electrical heating means associated with one of said elements, second electrical heating means associated with the other of said elements, the input signal being connected in series With said first means and a rst voltage source, the input .signal further being connected in series with said second means and a second voltage source, whereby said thermomechanical elements are heated differentially in response to varia- 15 tions in amplitude of the input signal, the rate of heating and cooling of said thermomechanical elements in respense to said first and second heating means being slow compared to the normal rate of change in amplitude of said input signal, and means operatively associated with said thermomechanical elements and movable under the joint influence thereof, said last-named means producing an output signal that varies in amplitude in proportion to the net movement thereof by said thermomechanical 10 elements.

References Cited in the file of this patent UNITED STATES PATENTS 1,886,439 Wells Nov. 8, 1932

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