Abstract: A gob distributor comprising a head inclining at least one gob scoop relatively displaceable through a predetermined angular range. The gob scoop can be displaced by structure which includes a ball screw, a nut, a housing, and a carriage secured to the nut. The carriage has an upstanding arm which will strike a selectively located and contained compression pad in the event the ball nut is displaced beyond its intended range. The arm may also, prior to striking the pad, displace a plunger which will operate a control switch to disable the system.

Abstract: A gob distributor is disclosed having a head including at least one gob scoop having a pinion and a rack for interconnecting with the pinion so that the gob scoop can be rotatively displaced through a predetermined angular range. The rack is displaced by a ball screw assembly wherein a vertically oriented forked link having a bottom end and two vertically spaced top ends connects the rack to the ball screw nut. Each of the top ends is secured to ball screw nut so that the link can be reoriented relative to the ball screw nut about a vertical axis passing through the top ends to compensate for misalignment between the ball screw and the link and the bottom end is connected to the rack so that any out of parallelism in either a horizontal or a vertical plane between the link and the rack will be accommodated.

Abstract: An electronic system for automatically controlling the weight and shape of glass gobs in a molten glass feeder.

Abstract: A cathode ray tube faceplate press having an indexing table rotatable around a column normal to the table and having circular array of female molds concentric with the column. Index speed of the table is optimized by a barrel cam drive cut to provide smooth acceleration and deceleration which can be tolerated by the molten glass in the molds. A cam dwell precisely registers the table work stations avoiding the need for register pins and the delays they introduce. Acceleration and deceleration peak at about the one-eighth and seven-eighths position of the drive cycle following a generally sinusodial form.

Abstract: A gob distributor for directing glass gobs to glassware-forming sections. Most particularly, this relates to the automatic positioning of scoops receiving the glass gobs from the glassmaking apparatus and directing them into troughs of glassware-forming sections which are arranged in a bank. The gob distributor features an arrangement wherein the distributor may be converted to vary the number of scoops in a scoop group from one to three or more. Principal features of the gob distributor are the utilization of a servomotor which is a reversible DC motor for positioning a rack which controls the angle of the scoops, and a releasable ball screw drive.

Abstract: An electronic system for automatically controlling the weight of glass gobs in a molten glass feeder, through the regulation of the height of the rotatory tube with respect to the feeder orifice; the electronic system includes, in combination, a finished article, a weight detector, a tube position detector attached to said tube, at least a temperature detector and glass level detector at the feeder, each of which respectively providing signals representative of the weight of the finished article, of the height of the tube with respect to the feeder orifice, of the molten glass temperature in said feeder and of the glass level in the same; a data processor which receives and processes the signals of the detectors, in order to compare the weight of the finished articles with a predetermined weight for the same and relates the weight deviations with the temperature and level of the glass and the height of the tube, in order to provide synergistic tube height compensation signals in order to allow an adequate flo

Abstract: An improved system of speed control for glass article forming machines includes an operator's control panel which is provided with controls to feed to the system the geometry parameters of the glass article to be manufactured as well as the timing of the manufacturing cycle; a data processor capable of calculating the speed of each mechanism of the machine in response to the data received by said operator's control panel; an EPROM-erasable programmable read-only memory which is used to contain tables including sequence profiles for the opening of actuating valves and speed mechanism profiles; a table selector circuit which is coupled to said programmable memory and the said data processor to select sequence tables from said programmable memory and which is able to solve the speed equations by using the speed information that it receives from the said data processor, and which is also able to provide the starting times of the various mechanisms; a random access memory coupled to said table selector circuit and

Abstract: A displacement pick-up arrangement for the position detection of a plunger is a component of a pressing station of a section of an I.S. glass-forming machine in which a plunger is inserted into a mold recess of a parison mold holding a glass gob at this time, and includes a ring-shaped core which is carried by a piston rod mounted to said plunger. The core forms an actuating element for changing the inductivity of a coil which is arranged in a ring-shaped frame between a cylinder and a guiding cylinder for the plunger.

Abstract: An apparatus for controlling a gob distributor of an IS or RIS machine for manufacturing hollow glass articles. The apparatus comprises a hydraulic drive, which is connectible to a position control device associated with the gob distributor, so as to move the distributor in oscillating or swinging motions. The hydraulic drive is controlled by a valve which, in turn, is actuated by a computer unit. The electronic arrangement of the apparatus includes an adapter, a digital-analog converter operatively connectible between the valve and the adapter, a parallel interface and connectible to the latter, a computer, a memory, and a synchronizer. The apparatus affords swift, precise, and controlled deposition of a glass gob which leads to the production of a parison in glass article manufacture.

Abstract: Gobs of molten glass are sensed as they pass along a path (12) which leads to a mold arrangement (10) of a glassware forming machine. Ultrasonic radiation is transmitted towards a point on the path so that the radiation is reflected by the gob to a detector (30). One or more parameters of the radiation detected are compared with an equal number of expected parameters for the radiation and a signal indicating the presence of a gob is produced if the or each parameter is consistent with its equivalent expected parameter.

Abstract: A gob distributor for directing glass gobs to glassware-forming sections. Most particularly, this relates to the automatic positioning of scoops receiving the glass gobs from the glassmaking apparatus and directing them into troughs of glassware-forming sections which are arranged in a bank. The gob distributor features an arrangement wherein the distributor may be converted to vary the number of scoops in a scoop group from one to three or more. A principal feature of the gob distributor is the utilization of a servomotor which is a reversible DC motor for positioning a rack which controls the angle of the scoops.

Abstract: Apparatus for sensing the passage of a gob of molten glass through a gob deflector or gob guide wherein a quick-disconnect nipple is fixed in a radial opening adjacent the lower end of the gob deflector. A hollow, quick-disconnect housing which is adapted to fit over the nipple is formed with a longitudinal passage therethrough, a washer-shaped holder lying in a plane, normal to the axis of said passage and intermediate the ends thereof serves to support a phototransistor with its leads extending into an end of the passage. A radial hole in the side of said housing has an elongated armored, stainless steel cable fixed thereto and an elongated high temperature insulating sleeve covering a pair of Teflong insulated wires extends within the cable with one of the wires connected to the emitter lead on said transistor and the other wire to the collector lead on the transistor.

Abstract: A glass feeder plunger operating mechanism driven by an electric motor controlled by a programmable computer programmed to drive the motor in a predetermined manner in order to generate a predetermined motion profile of one or more glass feeder plungers. The plungers are secured to the end of a cantilevered lateral support bracket which is cyclically and vertically reciprocated by cyclical oscillations of the electric motor. The output shaft of the motor is connected to a ball screw in threaded engagement with a ball nut which is secured to a member connected to the plunger support bracket. The plunger support bracket is attached to a moveable vertical support shaft which maintains plunger alignment during the range of motion. The operating mechanism is attached to a frame which is adjustable in two dimensions to facilitate alignment of the plungers with their respective orifices. Air cylinders are provided to counter-balance the weight of the members being vertically reciprocated.

Abstract: A glass forming system having a plurality of machines, each of which includes a plurality of individual sections having movable components which operate in timed relationship with respect to one another. An electronic control system effects the automatic synchronous operation of the various individual sections of each machine to thereby automatically and continuously form hollow glass articles. The electronic control system includes a mini computer with associated storage units for storing data for controlling the operation of the glass forming machinery. Information is written into and read out of the mini computer by means of a printer and cathode ray tube console.

Abstract: The invention relates to the analysis of defects in materials such as molten glass. According to the invention, the material passes by a monochrome beam the wavelength of which is below 3.times.10.sup.-6 m. The radiation is diffused by any defects present in the material. The analysis of the defects is conducted dependent on the position of the receiver detecting the diffused rays and on the shape of the signal received. The invention permits a continuous analysis of a flow of glass supplying a fiber-making machine.

Abstract: Apparatus for manufacturing molded articles includes a plurality of mold section presses. A mold slide carriage of each press moves a mold among charge receiving, molding, and extraction stations. A charge is guided to the mold while at the receiving station by a trough, from a rotatable scoop. A mold clamp mechanism of drivable arms linked to the mold and wedgeable against cam blocks maintains the mold closed during molding. A mold plunger driven by a press head assembly mates the mold. A molded article is kicked up by a kick-up mechanism. A take-out mechanism rotates jaw members about two axes to grasp molded articles at the extraction station, lifting them to an article removal station.

Abstract: The bushing temperature measurement device is a microprocessor based sensor which determines the temperature across a multi-segment electrical resistance heated glass fiber producing bushing. The temperature change is determined by calculating the change in resistance of each segment of the bushing by sensing the voltage drop across that segment and dividing by the current flowing in that segment. All measurements of voltage and current are taken simultaneously and averaged over several cycles. The microprocessor, through appropriate output circuitry, alerts other process controls to eliminate any change in temperature.

Abstract: A new delivery system for use with glassware forming machines of the rotating table type having a plurality of continuously rotating spaced forming units spaced about the periphery thereof. The delivery system includes a plurality of gob guiding units each having a scoop, trough and deflector secured to a corresponding oscillating frame. A vertical pivot shaft supports each scoop and is operatively connected with an actuating means to move the corresponding scoop laterally between a delivery position and a reject position. The actuating means is responsive to a plurality of gob reject actuators in order to enable selective delivery or rejection of individual gobs of selected forming units.

Abstract: An apparatus for individually controlling the delivery of each gob within a group of gobs intended for simultaneous delivery to the molds of a section of a multiple section glassware forming machine. In a multiple gob multiple section glassware forming machine adapted to receive a plurality of gobs simultaneously at each successively activated section of the machine, a corresponding plurality of interceptors are associated adjacent the paths of the gobs and may be selectively activated to reject selected ones of the gobs in each cycle of the machine.

Abstract: A method and apparatus are presented for granulation of molten slag for determining the flow of molten slag and adjusting the supply of granulation water in accordance with the flow of molten slag.

Abstract: Controlling the level of molten material in a melting furnace is disclosed. The level of molten material is sensed downstream of the furnace and batch materials are choke fed to keep the total batch crust plus molten glass depth constant. This provides for simpler molten glass level control as melter power can be directly controlled in response to glass level.

Abstract: The invention involves a system for detecting power failures in a glass ware forming machine and for effecting either a programmed stop of the machine which permits removal of all molten glass in the machine prior to a shutdown or a more rapid emergency stop. Also a machine speed monitoring system shuts down the machine when the speed slows below a predetermined limit. A supplemental battery system is provided to maintain power during emergencies to permit a sequenced shut down. The programmed control is organized to shut down the elements of the machine to initialized positions.

Abstract: A timing control system for the gob delivery system of a glassware forming machine of the rotating table type. Gob timing functions provide means to determine the drop times of each gob within a group of gobs. Adjusting means are provided to adjust the drop times of selected gobs to equalize drop times of all gobs within a group of gobs being delivered.

Abstract: The machine has a plurality of individual glassware forming sections each having a plurality of glassware forming mechanisms and means for distributing gobs of molten glass to each of the individual sections in an ordered sequence over one machine cycle consisting of a fixed number of clock pulses by cycling the forming mechanisms in a predetermined sequence of forming steps. Each individual section has an electronic control system responsive to each clock pulse for providing a load signal and forming signals to actuate the forming and a circuit for providing a gob load signal in response to a load signal from any one of the control systems and means responsive to the absence of a gob load signal for deflecting a gob from being distributed to an individual section.

Abstract: The present invention is a computer control system for a glass factory having a plurality of individual section glassware forming machines. The glass factory control system preferably comprises four microprocessor systems, respectively responsible for overall factory control, overall shop control, individual shop control and individual section control. At the most general level, a microprocessor called the factory supervisory computer performs such functions as scheduling jobs, controlling inventory, forecasting sales, determining fuel availability and cost, performing IS machine simulation and providing maintenance information. At the next level, another microprocessor called the console computer stores and manages all job history files, provides shop status information on demand and collects selected production data. Each shop computer performs such functions as controlling a stacker motor, monitoring temperatures, storing section status information and storing job timing information in nonvolatile storage.

Abstract: A method and apparatus for controlling the delivery of gobs to each section of a multiple section glassware forming machine to assure that no one section can authorize the delivery of a gob of molten glass to any other section. The invention discloses means for monitoring the time of occurrence within a machine cycle of the delivery enable pulse from each section and for determining whether this delivery enable pulse occurs within a predetermined time window. In the event either the leading or trailing edge of this pulse occur outside predetermined time windows, the gob interceptor associated with the machine is activated to reject the gobs intended for that section. The invention also discloses means for monitoring the motion of a gob interceptor to provide assurance to an operator that the interceptor has moved to either a delivery or intercept position in a timely manner.

Abstract: Apparatus for sensing the position of a mechanism while moving in a direction transverse thereto is disclosed. The apparatus for sensing the position of the mechanism comprises an electrical load, an oscillator having an input connectable in series with the load to a source of direct current, and an electromagnet electrically connected to the output of the oscillator and having a radiating surface opposingly positioned to face the mechanism so that a magnetic field generated thereby radiates in a direction toward a fixed target position through which the mechanism travels. The apparatus also comprises an electrically conductive target having a surface between a leading edge and a lagging edge. The target is mounted on the mechanism so that the leading edge of the target enters the magnetic field as the mechanism moves the target toward the target position.

Abstract: A signal is produced which is representative of a position of a part of a mould (1b, 7b, 8b, 9b) at a time in a cyclic process of forming glassware when the mould (1, 7, 8, 9) should be closed. This signal is compared with a signal representative of the position of the mould part (1b, 7b, 8b, 9b) when the mould is correctly closed. This latter signal is produced by averaging a selected number of the immediately preceding signals representative of the position of the part of the mould at the time when the mould should be closed.

Abstract: A programmable control signal generator controls the overall speed of an I.S. machine, the timing of sequential functions of each individual section, and the relative phasing of the IS machine sections. A time-based drive signal, derived from the time base signal of the programmable control signal generator, is applied to a stepper motor which is coupled to a gob feeder and plunger mechanism and a conveyor mechanism through respective gear reducers. The pulse repetition rate of the drive signal is controlled manually from an operator's speed control station or automatically from a computer to establish and vary the machine speed. The programmable control signal generator also provides a timing signal, coordinated with the drive signal, to time the sequential functions of the sections as a function of the number of elapsed time increments into which a machine cycle is divided. The timing signal has a pulse repetition rate which is preferably a calculated ratio of the repetition rate of the drive signal.

Abstract: An arrangement for adjusting the mass of gobs of thermoplastic material, especially molten glass, which are deformed in a positive manner in the mold of a molding machine by means of a pressing member which penetrates into the gobs. A distance transducer mechanically detects the maximum depth of penetration reached by the pressing member during each molding-machine operating cycle. The distance transducer is connected with a metallic actuating element for a differential transducer, at whose output is produced an electrical signal proportional to the maximum penetration depth reached, this signal being applied to an automatic regulating circuit which adjusts the setting of a dosing structure which controls the mass of the gobs.

Abstract: Improved system for controlling the movement of rotary article conveying mechanism in IS glassware forming machines employing a reversing arm, operating mechanism for said arm to move same between a parison forming station and a blow molding station, said operating mechanism including a double action fluid driven actuator, solenoid controlled valves for the actuator, an arm position sensor, an actuator pressure sensor, a logic circuit receiving signals from the sensors, a digital valve responsive to signals from the logic circuit for fluid flow control from the actuator, a regulator controlling fluid pressure to the actuator, and a control panel containing digital indicators, mode switches and a mode indicator and a digital display for reception and transmission of signals to and from the logic circuit, the end result being the precise timing of reversing arm operation and elimination of impact at the end of reversing arm movement, with identical operational mechanism for the take-out arm, with the additional

Abstract: A method and apparatus for automatically stopping an automatic glassware forming machine in an orderly sequence of steps. When it is desired to start the machine, a start routine is initiated to move the various glassware forming mechanisms into the appropriate starting positions such that the glassware forming cycle can begin. A stop routine is provided to cycle the glass from the machine and to move the various glassware forming mechanisms into a stationary position where they can be easily accessed. In accordance with the present invention, if the stop routine is intiated before at least one predetermined exit point in the start routine, the stop routine will be entered at an intermediate step such that only those steps concerned with moving the forming mechanisms into the final stationary position will be performed.

Abstract: The disclosure provides an improved construction for a ten-section IS glass forming machine which incorporates on and in the machine frame, all of the control valving and piping necessary to operate all of the sections of the machine according to any selected one of a plurality of different types of processes, resulting in a significant decrease in the proliferation of pipes and valves that were previously required to be added to, and then removed from, the machine as the machine operation was changed from one type of forming process to another. The apparatus of this invention further applies individual controls for effecting the cooling of each parison mold cavity and each blow mold cavity of each multi-cavity section of the machine.

Abstract: An electronic glass gob distributor for machines which form glassware, thermoplastic or similar articles, comprising one or more glass gob distributing channels each supported on its rotatable shaft, a step motor for actuating each rotatable shaft to move the associated distributor channel toward respective forming stations, a pulse signal generator for each step motor, a pulse amplifier for each glass gob distributor channel to amplify and feed the pulse controlling signals to the respective step motor, and a microcomputer programmer for controlled sequence of the generated pulse signals eminating from a data processing unit connected to an operator's control panel, with suitable conductors from the data processing unit to gob feed sensors and to distribution channel position sensors, with additional conductors to solenoids operating a pneumatic valve adapted to actuate a fluid operated linear motor for moving rejecting channels into gob receiving position to prevent feeding of a gob into the glassware formi

Abstract: A glass tube extrusion apparatus (50) is comprised of a chamber (52) having a crucible (72) therein mounted within and spaced from an inductive heating coil (77). As a glass tube (170) is extruded from an annular opening (74) in the bottom of the crucible (72) the tube is monitored for bending. When a bend starts to occur an X-Y motion apparatus (54) is activated to move the crucible (72) laterally within the coil (77) in a direction opposite to the bend to straighten the tube (170).

Abstract: An electronic control system for an automatic glassware forming machine includes a plurality of position sensors for monitoring the motions of individual glassware forming mechanisms. The sensors generate output signals which define the start and stop times and/or motion of the respective forming mechanisms. The electronic control is responsive to the sensor output signals for identifying any mechanical dead times in the forming cycle. Mechanical dead time is defined as time during which no machine motions are occurring, but could be occurring without interfering with essential heat transfer functions. The electronic control can then reduce or remove selected mechanical dead times to reduce the machine cycle length, and consequently, increase the production rate of the machine.

Abstract: A pair of glass ribbon edge detectors each have a power source connected to a carbon probe suspended over the molten metal bath of a glass forming chamber and to the molten metal bath to form a pair of capacitors. The voltage output of each capacitor has a first value when the probe is over the molten metal bath, a second value when the probe is over the glass ribbon and a third value when the probe is over a portion of the molten metal bath and a portion of the glass ribbon edge. Displacement and direction of displacement of each probe is used to determine glass ribbon width.A tweel for metering glass onto the molten metal bath has linear displacement gauges mounted at each side thereof and directly connected to the tweel so as to monitor displacement of the tweel to determine the flow of molten glass into the forming chamber. Movement of the tweel in response to the capacitors' output controls the flow of molten glass to control the ribbon width.

Abstract: A tweel flow control device at the entrance to a flat glass forming chamber is provided with overhead support and elevator means, preferably adapted to convey the tweel from its operative location.

Abstract: An improved glass melt tank (10) having a feeder (15) and a channel (14) which interconnects the tank and the feeder and in which is arranged a rotary, raisable and lowerable regulator (20, 21) which opens and closes the channel (14) so that the feeder (15) is supplied with molten glass from the tank (10) when a level sensing means (22) senses a lower level in the feeder, the supply of molten glass being caused to cease when an upper level is sensed. The regulator (20, 21) rotates continuously in order not to get stuck in setting glass and seals against a horizontal seat formed in the channel.

Abstract: A tweel flow control device at the entrance to a flat glass forming chamber is provided with suport means adapted for positioning the tweel in three dimensions.

Abstract: A method and apparatus for forming and delivering insulating glass in gob form to a lamp base making machine from a continuous stream of molten glass. A rotating dial severs the glass stream into uniform gobs and during rotation forms the gobs into a ball like form and delivers the gobs to a pair of radially spaced drop points for delivery to the base shells on an indexing base making machine.

Abstract: A receiver for waste molten glass, which automatically dumps the glass as cullet in lump or fragment form. The receiver comprises primarily a hopper or bin, with a central partition which divides the hopper into two compartments. The hopper or bin is pivotally mounted for reciprocating pivotal movement about a horizontal line in the plane of the partition such that the compartments formed on either side of the partition are alternately faced upwardly to receive molten glass and cooling water. Molten glass gobs, thus cooled, and water weight that side of the hopper in which they are received, thus causing it to pivot downwardly and thereby to dump cooled cullet in lump form while the alternative compartment is faced upwardly to receive subsequently poured waste molten glass and water until the weight of material in that compartment causes reverse pivotal movement and dumping. The hopper is triangular in vertical cross section, as are the partitioned compartments thereof.

Abstract: A machine for the manufacture of glass articles by blow moulding comprises a plurality of article-forming assemblies mounted in a circular array on a rotatable carousel. Each assembly has a number of operating means which cooperate to shape a gob of molten glass, first by rough-blanking using a plunger, and then by blow-moulding, into the required article. Control of said operating means is effected by a set of primary control members adjustably positioned in fixed locations around the carousel, and a respective set of carousel-mounted secondary control members associated with each assembly. As the carousel rotates, the secondary control members are moved past and influenced by corresponding ones of the primary control members and, as a result, the operating means of each assembly are appropriately controlled to shape the required article.

Abstract: A glass forming machine having a plurality of sections each of which includes a plurality of movable components which operate in timed relationship with respect to one another. An electronic control system effects the automatic synchronous operation of the various sections of the machine to thereby automatically and continuously form hollow glass articles. An automatic override system monitors each of the plurality of sections to determine whether each of the plurality of movable components are in the proper position at any given time. If the aforementioned movable components are not in the proper position at any given time, the machine is either stopped or the operation thereof modified to appropriately correct the operation of the machine.

Abstract: A programmable automatic controller for operating a section of a glassware forming machine having a plurality of components which operate in a timed or sequential relationship with one another. The controller includes a timing means for generating a digital signal in synchronism with the operation of the machine, wherein the digital signal provides an instantaneous indication of the time elapsed in each cycle of operation of the machine. A random access memory (RAM) stores the status of every section component at each increment of time during each cycle of machine operation. The digital signal addresses the RAM so that the statuses of all components for the corresponding time are directed to drivers which provide component enable or inhibit command signals.Control means for adjusting the actuation and deactuation times of the section components provide information of a computer which updates an internal memory table organized similarly to the RAM.

Abstract: Apparatus and method for measuring the volume and shape of a falling gob of glass. Two cameras are used to make section by section measurements of the horizontal extent of the moving gob. Timing of the measurements is controlled so as to cause measurements to be made at equal increments of the motion of the gob. The measurements are made 90.degree. apart with respect to the gob and are utilized to determine the volume of each section of the gob. The volumes of the individual sections of the gob are then summed to determine the total volume of the gob. An image of the gob is generated on a television screen to aid in the determination of the shape of the gob.

Abstract: A method and apparatus is disclosed for the production of plate glass. A glass melting furnace containing molten glass connects with an outflow furnace in such fashion that central layers of molten glass in the glass melting furnace are conveyed to the outflow furnace. The outflow furnace connects with an outflow nozzle which forms a flat glass band from which the plate glass is cut. The outflow speed of the glass band issuing from the outflow nozzle is regulated by a static pressure adjustment determined by a height of the molten glass in the separate outflow furnace. A supply channel to the nozzle preferably contains heating electrodes for resistance heating of the molten glass prior to issuance from the nozzle.

Abstract: A batch material feeder for an electrically heated opentop refractory furnace, particularly a circular furnace, wherein the feeder includes a trough holding batch material and mounted over the furnace top, there being a rotatable agitator within the trough for moving batch material over discharge openings in the trough bottom, so as to deposit the batch material over the top of the molten mass in a manner that provides for a thin uniform layer of batch while assuring proper control of the thickness of the deposited layer.

Abstract: An apparatus for detecting the presence of a gob of molten glass as it enters a cavity in the mold of an automatic glassware forming machine. The detector includes a phototransistor sensor and circuitry for generating a gob detection signal. Two or more detectors can be combined to generate a signal indicating that the last gob has entered a multi-cavity mold so that the forming process can begin. The gob detection signal can also be utilized to adjust the timing of the glassware forming process for differences in the travel time between the gob forming apparatus and the mold.

Abstract: A push button-actuated digital regulator circuit for use with inverter drives for use with inverter drives for A.C. motors of glassware manufacturing apparatus. The digital regulator responds to an operator is pushing UP and DOWN push buttons to increase or decrease the frequency of an oscillator output signal to the inverter. Maximum and minimum frequency limitations are preset at the oscillator and inhibit the operator command signal in the event a commanded increase or decrease would exceed one of the limits. A counter array provides adjustable frequency outputs to the inverter in binary-coded decimal. In a first embodiment, the circuit responds to continuous depression of one of the buttons by adjusting the output frequency at a rate established by an on-board oscillator. Alternatively, adjustment of the output over a plurality of frequency counts may require repeated pressing of the appropriate push button.