Automated energy systems with computer compatibility

Claims

What is claimed is:

1. A method for supervising energy systems in ON/OFF fashion by controlling the energy application to maintain a desired energy level comprising the steps of:

predetermining the desired energy level by establishing it as a number;

sensing the actual energy level of the system by exposing a variable output sensor means thereto for output variation in accordance with the sensed energy level;

converting the variable output to an adjustable pulse train with the time period between pulses being proportional to the energy level being sensed;

storing numbers having values in accordance with the ratios of sensor output variable values at the energy levels to be sensed to the sensor output value at a reference energy level, with said ration numbers being retrievable respectively against the desired energy level number;

selecting from the stored ratio numbers the predetermined desired energy level number;

establishing a reference standard time base as a source of clock pulses;

selecting that number of clock pulses from the time base occurring during the period between adjacent pulses of the pulse train;

determining if the selected number of clock pulses is grater than, equal to, or less than the selected number; and,

applying energy if required.

2. Apparatus for supervising energy systems in ON/OFF fashion by controlling the energy application to maintain a desired energy level comprising, in combination:

means for predetermining the desired energy level by establishing it as a number;

means for sensing the actual energy level of the system by exposing a variable output sensor means thereto for output variation in accordance with the sensed energy level;

means for converting the variable output to an adjustable pulse train with the time period between pulses being proportional to the energy level being sensed;

means for storing numbers having values in accordance with the ratios of sensor output variable values at the energy levels to be sensed to the sensor output value at a reference energy level, with said ratio numbers being retrievable respectively against the desired energy level number;

means for selecting from the stored ratio numbers the predetermined desired energy level number;

means for establishing a reference standard time base as a source of clock pulses;

means for selecting that number of clock pulses from the time base occurring during the period between adjacent pulses of the pulse train;

means for determining if the selected number of clock pulses is greater than, equal to, or less than the selected number; and,

means for applying energy if required.

3. The apparatus of claim 2 wherein;

said means for predetermining are switched and the number is represented in binary coded decimal;

said means for sensing is a resistance;

said desired energy level is a temperature;

said means for converting is an adjustable oscillator; and,

said means for selecting is a logic circuit.

4. The apparatus of claim 2 wherein;

said means for sensing is an uncalibrated resistance;

said means for converting is adjustable whereby a predetermined time interval is set at a known energy level; and,

said desired energy level is a temperature.

5. The apparatus of claim 2 wherein said energy levels are pressures and the sensor variable is resistance or voltage.

6. The apparatus of claim 2 wherein:

the sensor means variable output is a voltage;

said desired energy level is pressure;

said means for converting is an oscillator; and,

said means for selecting is a logic circuit.

7. The method of claim 1 wherein energy application is applied in discrete equal units of energy, each unit of which only slightly affects the actual energy level and is small compared to the predetermined energy level.

8. The method of claim 1 comprising the further step of storing the results of the determination to maintain energy application for a predetermined time period which is in excess of the time required for at least one determination.

9. The method of claim 1 including the further step of multiplexing pulse trains respectively associated with more than one energy level for comparison and application to the associated energy system.

10. A method for monitoring energy systems by indicating an unknown energy level by using a ratio change of sensor output comprising the steps of:

storing numbers having values in accordance with the ratios of sensor output variable values at the energy levels to be sensed to the sensor output value at a reference energy level, with said ratio numbers corresponding to unknown energy levels to be indicated;

sensing the actual energy level of the system by exposing a variable output sensor means thereto for output variation in accordance with the sensed energy level;

converting the variable output to an adjustable pulse train with the time period between pulses being proportional to the energy level being sensed;

establishing a reference standard time base as a source of clock pulses;

selecting that number of clock pulses from the time base occurring during the period betwen adjacent pulses of the pulse train;

counting the selected number of clock pulses to develop a ratio number; and,

indicating from the stored numbers the unknown energy level corresponding to said ratio number.

11. Apparatus for monitoring energy systems by indicating an unknown energy level by using a ratio change of sensor output comprising:

means for storing numbers having values in accordance with the ratios of sensor output variable values at the energy levels to be sensed to the sensor output value at a reference energy level, with said ratio numbers corresponding to unknown energy levels to be indicated;

means for sensing the actual energy level of the system by exposing a variable output sensor means thereto for output variation in accordance with the sensed energy level;

mans for converting the varaible output to an adjustable pulse train with the time period between pulss being proportional to the energy level being sensed;

mean for establishing a reference standard time base as a source of clock pulses;

means for selecting that number of clock pulses from the time base occurring during the period between adjacent pulses of the pulse train;

means for counting the selected number of clock pulses to develop a ratio number; and,

means for indicating from the stored numbers the unknown energy level corresponding to said ratio number.

12. The apparatus of claim 11 wherein:

said means for sensing is a resistance;

said unknown energy level is a temperature; and,

said means for converting is an oscillator,

13. The apparatus of claim 11 wherein:

said means for sensing is an uncalibrated resistance;

said unknown energy level is a temperature; and,

said means for converting is adjustable whereby a predetermined tine interval is set at a known temperature.

14. The apparatus of claim 11 wherein said energy levels are pressures and the sensor variable is resistance or voltage.

15. The apparatus of claim 11 wherein:

the sensor variable output is a voltage;

said unknown energy level is pressure; and,

said means for converting is an oscillator.

16. A method for monitoring energy systems to develop alarms when the system energy level is beyond a predetermined band of energy levels by using a ratio change of sensor output comprising the steps of:

establishing a desired energy level as a number;

storing numbers having vaues in accordance with the ratios of sensor output variable values at the energy levels to be sensed to the sensor output value at a reference energy level, with said ratio numbers corresponding to energy levels to be alarmed;

sensing the actual energy level os the system by exposing a variable output sensor means thereto for output variation in accordance with the sensed energy level;

converting the variable output to an adjustable pulse train with the time period between pulses being proportional to the energy level being sensed;

establishing a reference standard time base as a source of clock pulses;

selecting that number of clock pulses from the time base occurring during the period between adjacent pulses of the pulse train;

counting the selected number of clock pulses to develop a ratio number;

obtaining a number corresponding to said ratio number;

adding a predetermined number to said corresponding number;

comparing the result of the addition to the set point number;

alarming if the set point number is higher than the resulting number;

subtracting a predetermined number from said corresponding number;

comparing the result of the subtraction to the set point number; and,

alarming if the set point number is lower than the resulting number.

17. Apparatus for monitoring energy systems by indicating an unknown energy level by using a ratio change of sensor output comprising:

means for establishing a desired energy level as a number.

means for storing numbers having values in accordance with the ratios of sensor output variable values at the energy levels to be sensed to the sensor output value at a reference energy level, with said ratio numbers corresponding to unknown energy levels to be indicated;

means for sensing the actual energy level of the system by exposing a variable output sensor means thereto for output variation in accordance with the sensed energy level;

means for converting the variable output to an adjustable pulse train with the time period between pulses being proportional to the energy level being sensed;

means for establishing a reference standard time base as a source of clock pulses;

means for selecting that number of clock pulses from the time base ocurring during he period between adjacent pulses of the pulse train;

means for counting the selected number of clock pulses to develop a ratio number;

means for obtaining a number corresponding to said ratio number;

means for adding a predetermined number of said corresponding number;

means for comparing the result of the addition to the set point number;

means for alarming if the set point number is higher than the resulting number;

means for subtracting a predetermined number from said corresponding number;

means for comparing the result of the subtraction to the set point number; and,

means for alarming if the set point number is lower than the resulting number.

18. The apparatus of claim 17 wherein:

said means for predetermining are switches and the number is represented in binary coded decimal;

said means for sensing is a resistance;

said desired energy level is a temperature;

said means for converting is an adjustable oscillator; and,

said means for selecting is a logic circuit.

19. The apparatus of claim 17 wherein:

said means for sensing is an uncalibrated resistance;

said means for converting is adjustable whereby a predetermined time interval is set at a known energy level; and,

said desired energy level is a temperature.

20. The apparatus of claim 17 wherein said energy levels are pressures and the sensor variable is resistance or voltage.

21. The apparatus of claim 17 wherein:

the sensor means variable output is a voltage;

said desired energy level is pressure;

said means for converting is an oscillator; and,

said means for selecting is a logic circuit.

22. A method for monitoring energy levels to determine if a load is operating above, at, or below a predetermined energy level comprising the steps of:

exposing sensor means to the load to sense the level of energy operation thereof and produce a variable output in accordance with variation of said energy level;

producing a pulse train in the form of said variable output wherein the period time interval between pulses of said train is indicative of the energy level being sensed;

adjusting the producing of said pulses by establishing a predetermined time interval between adjacent pulses at a known energy level for said sensing and thereafter proportionately modifying the production of all pulses;

storing values in accordance with the ratio of sensor value at the levels to be sensed to the sensor value at a reference level;

producing many clock pulses in the least time interval to be encountered between said train pulses;

selecting the number of clock pulses occurring during an interval between adjacent pulses of said train; and,

comparing the number of clock pulses selected with the ratio number stored in said memory indicative of said predetermined energy level.

23. Apparatus for monitoring energy levels to determine if a load is operating above, at, or below a predetermined energy level comprising:

sensor means exposed to the load to sense the level of energy operation thereof and produce a variable output in accordance with variation of said energy level;

said sensor means comprising a sensor and means for producing a pulse train in the form of said variable output wherein the period time interval between pulses of said train is indicative of the energy level being sensed;

said means for producing being adjustable whereby a predetermined time interval is set between adjacent pulses at a known energy level for said sensor;

a memory having values stored therein in accordance with the ratio of sensor value at the levels to be sensed to the sensor value at a reference level;

a clock producing many clock pulses in the least time interval to be encountered between said train pulses;

means for selecting the number of clock pulses occurring during an interval between adjacent pulses of said train; and,

means for comparing the number of clock pulses selected with the ratio number stored in said memory indicative of said predetermined energy level.

24. The apparatus of claim 23 wherein:

said sensor means is a resistance;

said predetermined energy level is a temperature;

said means for producing is an adjustable oscillator; and,

said means for selecting is a logic circuit.

25. The apparatus of claim 23 wherein:

said sensor means is an uncalibrated resistance;

said predetermined energy level is a temperature; and.

said predetermined time interval is selected for a value of sensor resistance at a known temperature.

26. The apparatus of claim 23 wherein said energy levels are pressures and the sensor variable is resistance or voltage.

27. The apparatus of claim 23 wherein:

the sensor variable output is a voltage;

said predetermined energy level is pressure;

said means for producing is an adjustable oscillator; and,

said means for selecting is a logic circuit.

28. A method for supervising energy systems in ON/OFF fashion by controlling the energy application to maintain a desired energy level comprising the steps of:

predetermining the desired energy level by establishing it as a number;

sensing the actual energy level of the system by exposing a variable frequency output sensor means thereto for output frequency variation in accordance with the sensed energy level;

frequency converting the variable output to a pulse train with the time period between pulses being proportional to the energy level being sensed;

storing numbers having values in accordance with the ratios of sensor output variable values at the energy levels to be sensed to the sensor output value at a reference energy level, with said ratio numbers being retrievable rspectively against the desired energy level number;

selecting from the stored ratio numbers the predetermined desired energy level number;

establishing a reference standard time base as a source of clock pulses;

selecting that number of clock pulses from the time base occurring during the period between adjacent pulses of the pulse train;

determining if the selected number of clock pulses is greater than, equal to, or less than the selected number; and,

applying energy is required.

29. Apparatus for supervising energy systems in ON/OFF fashion by controlling the energy application to maintain a desired energy level comprising, in combination:

means for predetermining the desired energy level by establishing it as a number;

means for sensing the actual energy level of the sytem by exposing a variable frequency output sensor means thereto for output frequency variation in accordance with the sensed energy level;

means for frequency converting the variable output to a pulse train with the time period between pulses being proportional to the energy level being sensed;

means for storing numbers having values in accordance with the ratios of sensor output variable values at the energy levels to be sensed to the sensor output value at a reference energy level, with said ratio numbers being retrievable respectively against the desired energy level number;

means for selecting from the stored ratio numbers the predetermined desired energy level number;

means for establishing a reference standard time base as a source of clock pulses;

means for selecting that number of clock pulses from the time base occurring during the period between adjacent pulses of the pulse train;

means for determining if the selected number of clock pulses is greater than, equal to, or less than the selected number; and,

means for applying energy if required.

30. The apparatus of claim 29 wherein:

said means for predetermining are switches and the number is represented in binary coded decimal;

said means for sensing is a crystal; and,

said predetermined energy level is a pressure.

31. A method for monitoring energy systems by indicating an unknown energy level by using a ratio change of sensor output comprising the steps of:

storing numbers having values in accordance with the ratios of sensor output variable values at the energy levels to be sensed to the sensor output value at a reference energy level, with said ratio numbers corresponding to unknown energy levels to be indicated;

sensing the actual energy level of the system by exposing a variable frequency output sensor means thereto for output frequency variation in accordance with the sensed energy level;

frequency converting the variable output to a pulse train with the time period between pulses being proportional to the energy level being sensed;

establishing a reference standard time base as a source of clock pulses;

selecting that number of clock pulses from the time base occurring during the period between adjacent pulses of the pulse train;

counting the selected number of clock pulses to develop a ratio number; and,

indicating from the stored numbers the unknown energy level corresponding to said ratio number.

32. Apparatus for monitoring energy systems by indicating an unknown energy level by using a ratio change of sensor output comprising:

means for storing numbers having values in accordance with the ratios of sensor output variable values at the energy levels to be sensed to the sensor output value at a reference energy level, with said ratio numbers corresponding to unknown energy levels to be indicated;

means for sensing the actual energy level of the system by exposing a variable frequency output sensor means thereto for output frequency variation in accordance with the sensed energy level;

means for frequency converting the variable output to a pulse train with the time period between pulses being proportional to the energy level being sensed;

means for establishing a reference standard time base as a source of clock pulses;

means for selecting that number of clock pulses from the time base occurring during the period between adjacent pulses of the pulse train;

means for counting the selected number of clock pulses to develop a ratio number; and,

means for indicating from the stored numbers the unknown energy level corresponding to said ratio number.

33. The apparatus of claim 32 wherein:

said means for sensing is a crystal; and,

said unknown energy level is a pressure.

34. A method for monitoring energy systems to develop alarms when the system energy level is beyond a predetermined band of energy levels by using a ratio change of sensor output comprising the steps of:

establishing a desired energy level as a number;

storing numbers having values in accordance with the ratios of sensor output variable values at the energy levels to be sensed to the sensor output value at a reference energy level, with said ratio numbers corresponding to energy levels to be alarmed;

sensing the actual energy level of the system by exposing a variable frequency output sensor means thereto for output frequency variation in accordance with the sensed energy level;

frequency converting the variable output to a pulse train with the time period between pulses being proportional to the energy level being sensed;

establishing a reference standard time base as a source of clock pulses;

selecting that number of clock pulses from the time base occurring during the period between adjacent pulses of the pulse train;

counting the selected number of clock pulses to develop a ratio number;

obtaining a number corresponding to said ratio number;

adding a predetermined number to said corresponding number;

comparing the result of the addition to the set point number;

alarming if the set point number is higher than the resulting number;

subtracting a predetermined number from said corresponding number;

comparing the result of the subtraction to the set point number; and,

alarming if the set point number is lower than the resulting number.

35. Apparatus for monitoring energy systems by indicating an unknown energy level by using a ratio change of sensor output comprising:

means for establishing a desired energy level as a number;

means for storing numbers having values in accordance with the ratios of sensor output variable values at the energy levels to be sensed to the sensor output value at a reference energy level, with said ratio numbers corresponding to unknown energy levels to be indicated;

means for sensing the actual energy level of the system by exposing a variable frequency output sensor means thereto for output frequency variation in accordance with the sensed energy level;

means for frequency converting the variable output to a pulse train with the time period between pulses being proportional to the energy level being sensed;

means for establishing a reference standard time base as a source of clock pulses;

means for selecting that number of clock pulses from the time base occurring during the period between adjacent pulses of the pulse train;

means for counting the selected number of clock pulses to develop a ratio number;

means for obtaining a number corresponding to said ratio number;

means for adding a predetermined number to said corresponding number;

means for comparing the result of the addition to the set point number;

means for alarming if the set point number is higher than the resulting number;

means for subtracting a predetermined number from said corresponding number;

means for comparing the result of the subtraction to the set point number; and,

means for alarming if the set point number is lower than the resulting number.

36. The apparatus of claim 35 wherein:

said means for sensing is a crystal; and,

said desired energy level is a pressure.

The present invention relates to apparatus and methods for the control of energy application (usually to a load) and/or monitoring and alarming, all relative to pre-determined energy levels, which may be set. Basically, an energy parameter is applied to a load to maintain a fixed energy level at the load. Most of the circuitry and apparatus is able to handle most energy forms, permitting the use of many various types of parameters of energies. Usually, only the transducer need be changed to handle the different energy systems known to man. The various transducer output signals may be multiplexed for control purposes relative to one or more parameter inputs. Direct period transducers are typified by a pressure sensitive crystal directly delivering an output which includes a time base, i.e., megahertz, wherein the frequency changes as pressure applied to the crystal changes. The indirect period transducers require a sensor plus a period converter. For example, the use of a pressure sensitive strain gauge requires a resistance to period converter because it is the resistance parameter which is varying in accordance with the strain sensed. In either event, a pulse train output is obtained.

Viewed somewhat differently, the present invention comprises a special purpose computer capable of accommodating a great number of variables for control and monitoring purposes relative to predetermined energy levels without recourse to large scale general purpose computers, and wherein the basic circuitry enables the control regardless of the different parameter inputs. For example, energy levels within the contemplation of the present invention may be derived from e.g.:

Temperature

Pressure

Position

Moisture content

Speed

Angular velocity

Crystal vibration

Light

Color, or derivative thereof

Or any variable which can be measured in terms of a predetermined characteristic, such as an energy level. The present invention may be employed in the measurement field to determine the efficiency of energy applied to a load or to a given use, or it may be applied as an efficiency measure or basis for handling parameters appearing in various formulae, singly or in relation to other parameters of variables.

The invention uses the period of a digital pulse train as a comparison standard by converting same to a time increment and logically counting it off against a set or predetermined energy level for the application of further energy to attain the preset standard or the elimination of the application of further energy if the preset level has been attained. A transducer is provided for each energy system, the purpose of which is to convert a sensed energy level to a digital pulse train for input to the common circuitry of the invention. From this pulse train the period is derived by metering the time interval between two pulses. The metering is achieved by gating a time passed frequency or clock to a counter for the interval of time corresponding to the parameter period. The counter has been previously set to a count increasing to the predetermined energy level and it is downcounted from that level by the instantaneous parameter period in accordance with the clock pulses passed through the gate during the sensed period. If the stored count is greater than the period count, the down counter does not reach zero and the circuitry responsible for the application of energy to the load or elsewhere is programed to maintain full energy application. However, when the parameter or period count exceeds the stored count corresponding to the predetermined energy level, then the command is no longer present, thus no further energy application is made to the load.

The system provides for the application of energy in discrete amounts calculated to be just sufficient to nudge the load toward set point with sampling and logic being achieved during each discrete energy burst to determine if further energy is necessary to reach set point.

A memory is provided to insure that continuous energy application to the load may be had due to the high sampling rate in the event the load is below set point.

Normally, the pickup transducer characteristic is a non-linear function relative to the energy level parameter change. The system incorporates a read only memory as a storehouse point by point for the non-linear characteristic which must be known or predictable. Stated another way, the ROM is used to store, point by point, the predictable non-linear characteristic of the parameter to period transducer. To avoid the use of calibrated sensors a ratio may be stored in the ROM and this is explained by the fact that the point by point stored characteristic is the ratio of the transducer output value (period) at a parameter value relative to the transducer output value (period) at a reference parameter value. A plurality of input signals may be grouped and multiplexed and a plurality of groups may be multiplexed wherein different energy systems are handled by the various groups but preferably the energy system is the same within each group.

Finally, it should be noted that both direct and indirect input or sensing of transducer devices may be employed without change of the basic system. A resistance to period transducer capable of providing the transducer digital pulse train really comprises an analog to digital converter which may include a temperature sensitive resistor connected to control the frequency of an oscillator. Such an indirect converter may readily cope with energy systems for maintaining temperature, pressure or position.

Another example of indirect type analog to digital converters comprises the voltage to period transducer which is useful in connection with systems controlling angular velocity, moisture content and the like wherein a magnetic tachometer or a microwave attenuation device are especially useful.

Examples of a direct analog to digital converter include such devices as photo-tachometer (photo pulse train generator) and the use of direct crystal vibrations. Basically, the direct transducer includes time as the base against which its energy system is defined and thus it may be seen that a crystal when compressed changes its output frequency, vibration or period.

By incorporating multiplexing techniques, a great quantity of stations may be monitored or controlled wherein identical parameters, such as temperature are supervised at all stations and/or additional parameters such as pressure, speed or the like are supervised or monitored at one or more stations. For instance, one of the many stations to be controlled and monitored could be the input to an extruder head where one or many strands of a product could be flowing, such as in the extrusion of plastic fibers where a head may have as many as a hundred extrusion ports, the object being to maintain a constant flow of plastic polymer at a specific temperature.

The temperature can be controlled and/or monitored and it can be assumed that the flow will be maintained properly, provided the known or input pressure is within tolerable limits. In this example, the area of the ports determines the volume that is flowing at the given temperature and pressure. If there is a rupture or a restriction of a port or ports, such that the pressure increases or decreases beyond the allowable limits, and if the sensed temperature is proper, it is sensed that the flow (pressure) is improper and consequently, the product is improper.

In a system of many such extrusion points (heads) in a processing plant these points or stations are usually grouped in banks of 8, 16 or 32 and signals therefrom are multiplexed into a logic controller and/or monitor. It has been found that a read only memory (ROM) may be used for each group of stations for controlling and monitoring temperatures and a second ROM may be used for the same group where pressures are monitored. If, e.g., 16 stations are monitored and controlled, the temperature ROM serves the 16 stations, and a pressure ROM serves the same stations. The control and monitoring system is deemed as having two channels whereby position "one" of channel 1 and position "one"of channel 2 and position "sixteen" of channel 1 and position "sixteen"of channel 2 are scanned simultaneously. If the temperature is below set point, the control portion of the temperature monitoring channel provides an increment of energy to the polymer to increase its temperature. At the same instant of time, in the pressure channel, if the pressure were above or below prescribed alarm set points, an alarm condition is sounded with possible automatic shut-off of the station. Here, it is shown that 16 stations have temperature monitoring and control with an overriding pressure monitoring system.

Another advantage is that, from a practical standpoint, these extrusion ports, over a period of time, will become restricted slowly, and the pressure will rise slowly. When the pressure reaches a point beyond allowable tolerances, i.e., a predetermined allowable condition, the pressure head could be dismantled for cleaning and subsequent reinstallation. Another reason for pressure increase is that a certain number of the ports could become clogged. It is understood that this system could be multiplexed with any number of channels to satisfy any number of stations.

Another similar example is where a process is using steam as the energy source for doing work. When using super heated steam, it is important to know not only the temperatures at the input and outlet ports where work is being accomplished, but also the pressure and the moisture content of the steam. Temperatures and pressures can be handled similar to the examples cited above and moisture can be determined by projecting a microwave signal through the steam and collecting the microwave as an attenuated signal residue which can be sensed by a voltage level and converted to a period of time for further control or monitoring purposes.

The design of thermal energy systems and controls therefor encompasses the following considerations:

1. The thermal capacitance of the system is determined. This is related to the volume of the material and the specific heat of the material times the specific gravity of the material.

2. A heating element is closely coupled from a standpoint of thermal energy transfer to the load to be heated with a wattage capacity such that the heater can accelerate the temperature of the load at a rate of 2.degree. C. per second.

3. The sensor is located in a position relative to the heater and load to simulate and anticipate the temperature of the working surface of the heater and the response is such that it will change its temperature in the thermal system at a rate of 2.degree. C. in 30 milliseconds.

4. When it is known that the desired control temperature of the sensor is below set point, a minimum burst of energy (1/60 of a second (16.6 milliseconds) with a 60Hz power system) is applied to the heating element.

5. A second measurement of temperature is accomplished before the expiration of the energy burst to accomplish continuous power if the sensor remains below set point temperature.

Thus, it can be seen that there is no discernable overshoot or hunting possible. It is to be noted that a 1/60 of a second burst of energy will change the temperature of the thermal system 2.degree. C. divided by 60 or 0.033.degree. C. Although this would not be discernable with averaging analog techniques within 16 milliseconds and certainly not by a human, the effect of the minute burst of energy is recognisable by the logic of the control circuitry. Consequently, the maximum temperature above set point can only be 0.03.degree. C. It is further noticed that the sensor response, i.e., its change in degrees centigrade per second, is 33 times as responsive in time as compared to the temperature response of the thermal system as influenced by the heating element.

An advantage of this system is a very close control band, plus or minus 0.03.degree. C., typical of what is expected from a high resolution control system, without the undesirable undulating effects normally associated with on/off control. To achieve such stability the customary method is to use expensive and bulky proportional control with anticipatory and reset features.

The principles of the invention are also useful in a mechanical energy system where the mechanical inertia is analogous to the thermal capacitance of a thermal system. In other words, a minimum burst of energy will change the inertia of the mechanical system very slightly and yet a second measurement of the momentum would be accomplished while the minimum burst is administered. For instance, a DC motor may be used with an AC power source, a Triac, and a rectifier. The Triac passes one complete cycle of 60 Hz power as a minimum burst to the motor and work. Therefore, the necessity for proportional power for steady state input of energy is unnecessary with resltant substantial savings in dollars and complexity. It is to be noted that the Triac is preferably turned on at zero voltage and is not turned on again until after the complete cycle of power reaches zero, unless a command is issued. The same change in momentum as a result of the 1/60 of a second of energy can be computed and will be discernable to the logic control.

Another important feature of such a control system where power is turned on at zero voltage is that undesirable high frequency noise is eliminated.

Apart from temperature systems, now it has been known that moisture content of certain products has been an important factor; however, extensive use of microwave monitoring, which signals will penetrate most any product other than a metal, is now available by the present invention because heretofore the cost per station or measuring has been prohibitive. The present system time shares the expensive portion of the circuit to make a multipoint monitoring and control porcess system practical.

For example, a known weight of roast beef in a microwave oven usually cooks in proportion to moisture loss. The most succulent roast known to man is one cooked at a very low temperature for a long period of time to maintain the moisture content high such as, for example, a roast placed in an oven turned to warm or 200.degree. with the door left open and cooked all night. By employing the present invention in conjunction with a microwave oven, the magnitude of the microwave cooking power may be monitored and controlled to maintain the high moisture content desirable. This is done by utilizing a constant energy source and detecting the microwave energy emanating from the opposite side of the roast such that the absorbed microwave energy is the energy utilized in the cooking process and the residue or detected energy is monitored relative to a predetermined level of microwave energy to maintain the optimum microwave absorption, based upon a known curve of absorbed microwave energy versus time for a given moisture content for beef or other material even including wood.

With this type control a great number of microwave ovens can be operated at the same time to cook a great number of roasts with the circuitry enabling a single master control station to make comparisons to the same or different desired energy levels, according to the volume of roasts and type of meat being cooked.

As an input, the system requires an analog of the parameter being measured, which is time related to the value of the parameter, such as a crystal, which may be vibrating at a period proportional to pressure applied to it, its temperature or combination of both or possibly vibrating according to some other parameter such as the impinging radiation. This period of time may be used directly or after it is amplified, multiplied or divided. A second analog relative to the parameter may be a resistance change with either positive or negative co-efficient as long as it is predictable according to a linear or non-linear relationship. Such resistance changes are noticeable in measuring torque or force (strain gauge), weight, pressure (bourdon gauge) temperature (platinum or nickel RTD).

A third type sensor gives a voltage change which represents the parameter or change in the parameter according to a linear or non-linear relationship. An example of this is a variable-mu transformer or differential transformer which changes its output voltage according to a pressure or force exerted upon it.

The invention will be better understood from the following detailed description thereof when taken in conjunction with the following drawings, wherein:

FIG. 1 is a circuit diagram of one type resistance to period transducer;

FIG. 2 is a circuit diagram of a voltage to period transducer;

FIG. 3 is a block diagram of an indirect period transducer;

FIG. 4 is a block diagram of a direct period transducer;

FIG. 5 is a block diagram of a direct angular velocity to period magnetic reluctance sensor.

FIG. 6 is a block diagram of a binary set point representing ratio of