Abstract: Apparatus either for a specimen that is to be held in a jaw assembly of, for example, a dynamic thermal-mechanical testing system or for the jaw assembly itself wherein the specimen or jaw assembly, respectively, exhibits both self-resistive and self-inductive heating whenever a sufficiently large alternating (AC) electrical current is passed serially therethrough. In one embodiment, the specimen (200, 300) is fabricated from a material which undergoes self-resistive heating and in which suitable levels of eddy currents can be induced by and also includes an appropriately shaped heating section (205, 206; 305, 306) situated near each of two opposing ends thereof. In another embodiment, a metallic conductor (403, 403'; 503) is fabricated from a material which undergoes self-resistive heating, in which suitable levels of induced eddy currents can occur and which contains appropriately shaped and sized heating sections (406, 407; 406', 407'; 512, 512').

Abstract: A technique for in a thermo-dynamic material testing system for optically measuring changes in specimen size that occur during material testing. Specifically, a pair of jaws, one movable and one fixed, engage opposite ends of the test specimen and are controllably moved with respect to each other in order to impart a desired tensile or compressive force to the specimen. A fixed light source emits a planar light beam, typically collimated laser radiation, that is directed at the specimen by two mirrors mounted to the jaws and on one side of the specimen. One of these mirrors is secured to and moves with the moving jaw and directs the light beam toward the specimen along a transverse path; the other mirror is mounted to the fixed jaw. A fixed light receiver receives the light beam after it has passed over the specimen and has been reflected by a similar pair of mirrors mounted to the jaws but on the other side of the specimen.

Abstract: Apparatus for a dynamic thermal-mechanical material testing system that not only self-resistively heats and deforms a specimen, both under controlled conditions, but also substantially reduces adverse affects in specimen performance, such as magnetically induced motion and non-uniform specimen heating, that would otherwise result from magnetic fields which impinge upon the specimen and are caused by high heating currents flowing in the apparatus. This reduction is achieved by spatially locating high current carrying conductors used in the apparatus such that these conductors collectively generate substantially balanced, i.e. substantially equal, and opposite magnetic fields that effectively cancel each other out in a volumetric region in the apparatus which contains the specimen and particularly its work zone.

Abstract: Apparatus, and an accompanying method for use therein, for a dynamic material testing system, and particularly for one that tests a specimen by compressively deforming its work zone and that has independent control over specimen deformation (strain) and strain rate. The apparatus can also simultaneously direct resistance heat or conductively cool the specimen, under controlled conditions, in order to establish isothermal planes at a desired substantially uniform temperature throughout the specimen work zone before, during and after each compressive deformation thereof.

Abstract: Apparatus and accompanying methods for use therein for measuring and controlling weld indentation during resistance welding operations are disclosed. During a welding operation, the apparatus measures changes in a distance separating a reference point located on an electrode assembly and a region situated on the surface of the workpiece being welded wherein the region is not substantially indented by the electrode. Specifically, a distance measuring system first establishes the location of the surface relative to the electrode before any welding current is passed through the weld area. The indentation is repeatedly measured by detection of ultrasonic echoes from the surface of the material being welded. Such measurements are taken at frequent intervals during the current flow period during which the weld is being formed in order to determine on a continuous basis the indentation of the electrode into the surface. The welding power may be terminated when the measured indentation reaches the desired value.

Abstract: Apparatus for determining the root-mean-square value of a pulsatile signal generated from a power line signal. Samples of the pulsatile signal are produced at predefined substantially equal sampling intervals beginning at substantially the onset of a pulse in said pulsatile signal and continuing thereafter for substantially the entire duration of a half period of the power line signal to generate corresponding sampled values. The sampled values are squared and accumulated, then divided by the total number of samples taken and accumulated during said half period to yield an intermediate value for which the square root is determined, resulting in the root-mean-square value of the pulsatile signal.

Abstract: A multi-channel electronic waveform recorder, for storing waveform data and time of occurrence information, i.e., a "time-tag", for each stored value of an input waveform, is disclosed. Specifically, each channel of the waveform recorder compares a previously stored value of a corresponding input signal to a current value, and stores the current value whenever the difference between the input signal and the previously stored value is a predetermined amount.

Abstract: Apparatus, for use in a servo-control system and which provides a smooth "bumpless" transition while switching from one transducer feedback signal to another, is described. Specifically, with this apparatus, a plurality of tracking signals are first produced in which each signal has a value which, in response to the value of a corresponding select signal, either tracks the feedback signal produced by a corresponding one of a plurality of transducers or remains constant. Each of these tracking signals is then subtractively summed with the feedback signal produced by the corresponding transducer in order to produce an output signal. Each of the output signals is then fed-back and subtractively summed with a command signal and the resulting difference, in turn, is applied as an error signal to a servo-amplifier. The values of all the select signals are set, by illustratively a process computer, in accordance with the particular transducers being switched.

Abstract: A multi-channel electronic waveform recorder, for storing waveform data and time of occurrence information, i.e., a "time-tag", for each stored value of an input waveform, is disclosed. Specifically, each channel of the waveform recorder compares a previously stored value of a corresponding input signal to a current value .Iadd.of that signal.Iaddend., and .[.stores.]. .Iadd.is able to store .Iaddend.the current value whenever the difference between the input signal and the previously stored value is a predetermined amount. .Iadd.Each or any selected sub-set of all the channels, through an appropriate switch setting, can determine points in time when, in response to the difference occurring for that channel, all the channels will simultaneously store the current value of these respective input signals. .Iaddend.