US3753259A

US3753259A - Cooler and freezer failure warning system

Info

Publication number: US3753259A
Application number: US00175976A
Authority: US
Inventors: R Donovan
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-08-30
Filing date: 1971-08-30
Publication date: 1973-08-14
Anticipated expiration: 1990-08-14

Abstract

Cooling failure warning system for a refrigerated food case or the like, including a source of a rectified, pulsating, supply signal, a source of a lower regulated signal supplied by the supply signal source, a temperature sensor installed in a selected location of the food case and responsively variable in resistance according to its sensed temperature, means responsive to the sensor resistance for producing a switch signal at a predetermined overtemperature condition, means responsive to the switch signal for producing a delayed switch signal, a temperature alarm device, and an alarm switch responsive to the delayed switch signal for applying the supply signal to energize the temperature alarm device. The warning system further includes fail-safe provisions for producing an alarm in the event of sensor failure. A power failure alarm device responsive to a loss of the regulated signal can also be included in the warning system.

Description

atent 1 1 Waite States Donovan 1 Aug. 14, 1973 [76] Inventor: Raymond L. Donovan, l027-20th St., Santa Monica, Calif. 90403 22 Filed: Aug. 30, 1971 21 Appl.No.: 175,976

[52] 11.8. C1. 340/228 R, 340/248 B, 340/412 [51] llnt. Cl G08b 21/00, G08b 23/00 [58] Field of Search 340/228 R {56] References Cited UNITED STATES PATENTS 2,832,947 4/1958 Patchell 340/228 R 2,992,120 7/1961 Elsken i 340/228 R 3,220,206 11/1965 Armentrout 340/228 R 3,283,579 11/1966 Josephs 340/228 R 3,594,752 7/1971 Alton 340/228 R Primary Examiner-Thomas B. Habecker [57] ABSTRACT Cooling failure warning system for a refrigerated food case or the like, including a source of a rectified, pulsating, supply signal, a source of a lower regulated signal supplied by the supply signal source, a temperature sensor installed in a selected location of the food case and responsively variable in resistance according to its sensed temperature, means responsive to the sensor resistance for producing a switch signal at a predetermined overtemperature condition, means responsive to the switch signal for producing a delayed switch signal, a temperature alarm device, and an alarm switch responsive to the delayed switch signal for applying the supply signal to energize the temperature alarm device. The warning system further includes fail-safe provisions for producing an alarm in the event of sensor failure. A power failure alarm device responsive to a loss of the regulated signal can also be included in the warning system.

14 Claims, 3 Drawing Figures Patented Aug. 14, 1973 2 Sheets-Sheet 1 I N V E NTOR. Ma/vpl. flan 014M COOLER AND FREEZER FAILURE WARNING SYSTEM BACKGROUND OF THE INVENTION This invention relates generally to warning and alarm systems. More particularly, the invention relates to a highly foolproof, cooling failure warning system for chilled or frozen food display cases, refrigerated storage chests and other similar enclosures.

In the modern large food stores or supermarkets, multiple refrigerated food cases providing open storage of chilled or frozen foods are usually utilized. For greater efficiency and ease of maintenance, the refrigeration system has been removed from each food case and all such systems centralized at a common location. Open storage, of course, requires substantially greater tonnage to maintain a given food temperature. Further, two or three circulating air fans are used to provide two or three separate forced air paths within each case to minimize the temperature gradients which can keep one section of a case cold and another section near, and occasionally above, thawing. In addition, one, two and sometimes three air baffle fans are used to provide dynamic air baffles which act as an air curtain preventing a stores ambient air from entering into the open storage areas of a case.

A constant knowledge of the temperature of the air surrounding the chilled or frozen foods in their cases provides the only positive protection to a store owner for his merchandise. Where the multiple case refrigeration systems have been centralized at a common location, suitable protection of the foods can be obtained by accurately monitoring the supply air temperature from the coolingcoils to the case interior. For greater and more complete protection of the foods, however, the temperatures of the separate forced air paths and of the discharge side of the dynamic cold air stream (air curtain) across the open face of the case should also be accurately monitored at the same time. Thus, a versatile temperature alarm system which is accurate and reliable is required.

Positive protection of chilled and frozen foods is achieved when such foods are totally immersed in a gradient-free atmosphere which is constantly maintained throughout the storage volume at the optimum temperature recommended by the food supplier. In

order to accomplish this, the alarm system must moni-' tor all critical areas of the food case continuously, and automatically generate an alarm when a predetermined overtemperature condition has persisted for a period slightly in excess of the time occupied by a defrost cycle and the time normally required to return the case to a point just below the predetermined overtemperature condition. This alarm, of course, must be prevented during legitimate defrost cycles; i.e., there should be a defrost cycle alarm override. It is noted that the on/off pulsing types of defrost cycling have been largely eliminated and timed (hot gas or electrically heated) defrosting cycles are employed in the modern, multiple case, high-powered refrigeration systems.

Different types of foods must be maintained at respectively different optimum temperatures and, therefore, require different alarm temperature settings in a temperature alarm system. In the prior alarm systems, however, the alarm temperature must be specified for the particular type of food to be protected, and a system is normally factory-adjusted so that its alarm temperature is unalterable. Thus, different types of foods would require different alarm units which are noninter' changeable. Further, such prior alarm systems commonly use specially designed sensors of specific masses wherein each mass provides a finite delay in the response time of the sensor to a change in temperature. This thermal response time therefore serves as a limited automatic defrost cycle alarm override. There is, however, no adjustment possible of the defrost cycle alarm override period and a fixed delay equal to the longest defrost cycle which might be encountered must be used. This clearly restricts the use of the sensor to refrigeration systems having suitably long defrost cycles. It is also noted that in the prior alarm systems, a loss of supply power to a system or the ordinary (open circuit) failure of the sensor itself is not reflected by an alarm and can go undetected for an extended time.

SUMMARY OF THE INVENTION Briefly, and in general terms, this invention is preferably accomplished by providing a cooling failure warning system for a refrigerated food case and the like wherein the warning system includes a source of a rectified, pulsating, supply signal, a source of a lower regulated signal supplied by the supply signal source, at least one temperature sensor installed in a selected location of the food case and responsively variable in resistance according to its sensed temperature, means responsive to the sensor resistance for producing a switch signal at a predetermined (adjustable) overtemperature condition, a timing switch responsive to the switch signal for initiating operation of adjustable delay means to produce a timed output signal therefrom, temperature alarm means, and an alarm switch responsive to the timed output signal for applying the supply signal to the temperature alarm means.

The warning system preferably further includes failsafe means for producing an alarm from the temperature alarm device in the event of failure (open or short circuit) of the sensor. A power failure alarm circuit including a power alarm device responsive to a predetermined loss (preferably a substantially total loss) of the regulated signal completes the implementation of a highly foolproof and adjustably versatile warning system. The utilization of rectified, pulsating, supply and regulated signals provides a more stable system with lower dissipation and less transient effects therein. The

timing and alarm switches are preferably silicon controlled rectifiers, for example, which control conduction of the rectified, pulsating, supply signal therethrough and thus can be rapidly and effectively turned off. This warning system is, therefore, also an extremely reliable and long-life system.

BRIEF DESCRIPTION OF THE DRAWINGS any cooling failure thereof; and

FIGS. 2A and 28, together, comprise a eircuit diagram of a cooler or freezer cooling failure warning system including the temperature alarm unit and three of the sensors shown in FIG. 1.

DESCRIPTION OF THE PRESENT EMBODIMENT In the accompanying drawings and following description of an exemplary embodiment of this invention, some specific dimensions, component values and types of components are disclosed. It is to be understood, of course, that such dimensions, values and types of components are given as examples only and are not intended to limit the scope of this invention in any manner.

FIG. 1 is a frontal perspective view of a temperature alarm unit 10 and sensor 12 which are constructed according to this invention for use with coolers and freezers to provide a warning of any cooling failure thereof. Generally, the unit 10 is contained in a metal case 14 approximately inches wide, 4 inches deep and 3 inches high, and weighs about 1.75 pounds. The sensor 12 includes, for example, a small diameter aluminum tube 16 approximately 4 inches long mounting a precision thermistor disc 18 therein. The tube 16 is preferably filled with a moisture excluding potting compound, and the sensor 12 is supplied with a cable 20 which is preferably about 12 feet long. The sensor 12 is a temperature averaging device which does not reflect short duration temperature changes such as occasioned by customers interrupting the air path to remove food articles from the food case. The sensor tube 16 is constructed of a material and length to permit accurate and repeatable temperature measurements in a very light air current or when in physical contact with some metallic portion of the cold air discharge outlet structure. The unit can operate with a single sensor 12, with two such sensors in series or with up to three such sensors in series, depending upon the degree of sensitivity (degrees of temperature change required to set off an alarm) desired for any particular installation. The multiple sensors must, of course, be used within enclosures which are supplied by the same cooling system and having the same defrost cycle.

The unit 10 can be firmly attached with its back nearly flush to a flat upright surface. Since all adjustments are located (recessed) in the bottom of the unit 10, however, it is preferably mounted upright on a shelf or flat horizontal surface to prevent any tampering of such adjustments. In this instance, only three

indicator lamps

22, 24 and 26 are readily visible to the customers. The power lamp 22 is green, for example, and when energized indicates that the unit 10 is turned on and regular 1 17 volts, 60 Hertz power is being supplied to the unit. The defrost lamp 24 can be amber and, when energized, indicates that the monitored food case is undergoing a defrost cycle or that it is in an early phase of cooling failure so that caution should be observed. Finally, the alarm lamp 26 is preferably red and, when energized, is a warning indicating that the cooling air to the case has persisted at a temperature exeeding the preset alarm setting for a period slightly in excess of a defrost cycle and the time normally required to return the case cooling air to a temperature just below the preset alarm setting.

FIGS. 2A and 2B, taken together, comprise a circuit diagram ofa cooling failure warning system 28 employing the temperature alarm unit 10 and three of the sensors 12 shown in FIG. 1. The system 28 can be broadly grouped into eight

functional circuits

30, 32, 34, 36,

38, 40, 42 and 44. The functional circuit 30 includes a polarized alternating current (AC) plug 46, a double pole, single throw control switch 48 and power indicator lamp 22. The switch 48 is, of course, the on-off switch for the system 28. When the switch 48 is closed, the leadsfand g are connected together, power lamp 22 is energized and regular AC service power is applied to functional circuit 32. The functional circuit 32 includes a stepdown transformer 50 and a full wave diode bridge rectifier 52. The power from circuit 30 is applied to the primary of the transformer 50 and its secondary is connected across the centers of the bridge rectifier 52. An output is obtained between the ends of the bridge rectifier 52 and this output is connected by leads a and e to the functional circuit 34.

Functional circuit 34 is a reference divider network including a series connection of resistors R1, R2, R3, R4 and R5, and a Zener diode CR1 connected across the last four resistors as shown in FIG. 2A. The output of the bridge rectifier 52 is connected by the leads a and e to the outer ends of the resistors R1 and R5. The resistors R3 and R5 are connected as rheostats, and the resistor R4 is a potentiometer. The common junction between the resistors R1 and R2 is connected to a lead b, the the common junction between resistor R2 and rheostat R3 is connected to a lead 0 and the wiper of the potentiometer R4 is connected to a lead d. The ends of the rheostat R3 are connected to connector 54 to which are connected the external series temperature sensors 12a, 12b and 12c. Of course, only one or two sensors can be used so that the rheostat R3 would be suitably adjusted in each instance to produce a predetermined parallel resistance of the rheostat and the sensor or series sensors.

A rectified supply signal S of a pulsating waveform appears on the lead a, and a regulated signal y of a clipped pulsating waveform appears on the lead [2. For a 60 Hz. line power signal, the rectified supply and regulated signals S and y are Hz. pulses as indicated in FIG. 2A. Adjustment of the potentiometer R4 sets the minimum response temperature for enabling the system 28 to an alarm condition, and adjustment of the rheostat R5 sets the temperature range (between 40 and +60F, for example) in which any desired alarm temperature can be set by the potentiometer R4. The sensors 12a, 12b and 12c vary inversely in resistances with sensed temperature so that the overall resistance between the ends of rheostat R3 decreases with increasing temperature and, conversely, increases with decreasing temperature. The net result is, of course, a variation in voltages on the leads 0 and d with the sensed temperature.

The leads a, b, c, d, e,fand g are connected to different functional circuits shown in FIG. 2B. The lead I; is connected by a resistor R6 to the collector of transistor Q1 which is connected as an isolation emitter follower amplifier in functional circuit 36. Lead c is connected through Zener diode CR2 12 volts breakdown, for example) and series resistor R7 to the base of the transistor Q1. The lead d is also connected through resistor R8 to the base of transistor Q1. The transistor Q1 base is connected through stabilization thermistor S6 and series resistor R9 to lead e. The normal drift which occurs in solid state circuitry when the surrounding ambient temperature varies is compensated for by the thermistor 56 over, for example, a range from 55 to 1 10F. The transistor Q1 base is also connected to lead c by a bypass capacitor C1 which prevents circuit oscillation. The emitter of the transistor O1 is connected to lead e by resistor R and an output is provided on lead h.

When the temperature sensed by any of the sensors 12a, 12b and 120 (FIG. 2A) reaches or exceeds the alarm temperature set by the wiper of potentiometer R4, the sensor resistance decreases such that the voltage on lead (1 increases sufficiently to turn on the transistor Q1 and produce an output signal on the lead h. It may be noted at this time that in the event that a sensor fails; i.e., has an open circuit, the overall sensor and rheostat R3 resistance is increased to such an extent that the voltage on lead c rises enough to break down the Zener diode CR2 and turn on the transistor Q1. Thus, the system 28 includes a fail-safe circuitry which constantly monitors the condition of the sensors 12a, 12b and 12c, and will automatically produce an alarm output in the event of either an open circuit excess undertemperature condition or short circuit (high overtemperature condition) failure of any of the sensors.

The lead h is connected to the gate of a silicon controlled rectifier CR3 in the functional circuit 38 (FIG. 28). Lead a is connected to the anode of the rectifier CR3 by resistor R11 and parallel defrost (caution) indicator lamp 24. The lamp 24 is, for example, a 28-volt direct current (DC) lamp. The lead e is connected to the cathode of the rectifier CR3. Lead b is connected to the base of a transistor Q2 by resistor R12 and such base is connected to the anode of rectifier CR3 by another resistor R13. The lead b is also connected to the emitter of transistor Q2 by a resistor R14, and the transistor collector is connected to lead e by series resistors R15 and R16. A filter capacitor C2 is connected across the resistor R16, and another cpaacitor C3 is connected between the lead b and the collector of transistor Q2 partly for preventing circuit oscillation. The collector of the transistor Q2 is connected to output lead i, and the common junction between resistors R15 and R16 is connected to a lead j.

The rectifier CR3 functions as an overtemperature (or undertemperature) switch with the lamp 24 serving as a visual indicator. The transistor O2 is connected as an alarm enabling trigger amplifier. On overtemperature, the transistor Q1 conducts and provides an output signal on lead h to fire the rectifier CR3. This energizes the defrost (caution) lamp 24 and turns on the transistor Q2. An output trigger signal (of approximately 16 volts, for example) is provided on the lead i. At the same time, a smaller signal (of approximately 5 volts, for example) is provided on the lead j. At the end of the defrost cycle or when the over-temperature is returned below the alarm temperature setting, the transistor Q1 is turned off and the signal on lead h is removed. Since the supply signal S (FIG. 2A) on lead a is of a rectified pulsating waveform, the fired rectifier CR3 is immediately turned off when the waveform drops to zero. Of course, the defrost (caution) lamp 24 is extinguished and the transistor O2 is also turned off.

The lead 1' is connected to a resistor R17 which is connected in series with an adjustable resistor or rheostat R18 in the functional circuit 40. The rheostat R18 is, in turn, connected in series with capacitor C4 to the lead e. The common junction between the rheostat R18 and capacitor C4 is connected to the base'of transistor Q3 by resistor R19, and to the leadj by a (germanium IN695) diode CR4 as shown in FIG. 28. Lead b is connected to the collector of transistor Q3 by resistor R20 and its emitter is connected to lead e by resistor R21. The lead b is also connected to the collector of transistor Q3 by the series arrangement of a capacitor C5, resistor R22 and Zener diode CR5 (8.2 volts breakdown, for example). The common junction of capacitor C5 and resistor R22 is connected to the base of transistor Q4. Lead b is connected to the emitter of the transistor Q4 by resistor R23, and the collector is connected to lead e by resistor R24. The transistor 04 is the alarm driver amplifier providing an output signal on lead k when turned on.

An adjustable time delay can be set by the rheostat R18 and the triger signal on lead i charges the capacitor C4 accordingly so that the transistor 03 is turned on and conducts when its base voltage reaches and exceeds about 0.6 volt, for example. The resistor R17 produces a fixed delay of approximately 15 minutes with the capacitor C4 whereas the rheostat R18 can provide an adjustable delay to approximately 60 minutes, for example. When the transistor Q3 conducts, the voltage across the Zener diode CR5 'is increased such that it breaks down. The capacitor C5 then charges and when the base potential of transistor O4 is sufficiently lower than that of its emitter, this transistor also conducts and produces an output alarm signal on the lead k. The resistor R22 is selected so that the resultant charging circuit with the capacitor C5 provides a fixed delay of approximately l5 minutes, for example. Thus, the functional circuit 40 provides an alarm delay of a minimum of 30 minutes, which can be adjustably increased an additional 60 minutes to an overall maximum of minutes.

When an overtemperature condition persists longer than the overall delay as set by the rheostat R18, an output alarm signal is produced on lead k and applied to the gate of a silicon controlled rectifier CR6 in the functional circuit 42. The cathode of the rectifier CR6 is connected to lead e, and its anode is connected to lead a through the alarm (warning) indicator lamp 26. A small AC annunciator 58 or a buzzer can be connected in parallel with the alarm lamp 26 as shown in FIG. 2B. The anode of the rectifier CR6 is also connected to one terminal of an external alarm connector 60, the other terminal of which is connected to lead a through a limiting resistor R25. The resistor R25 is provided to limit the current flow in the event of a short in the external alarm circuit. The resistor R25 is preferably mounted outside the metal case 14 (FIG. 1) or to a suitable heat sink. Of course, other current limiting devices including fully limiting or automatically isolating (switch) means can be used in place of the resistor R25. The alarm signal on lead k fires the rectifier CR6 so that the rectified pulsating signal on lead a is applied to energize the alarm lamp 26, annunciator 58 and any external alarm or system connected to the connector 60.

When the extended overtemperature condition is corrected, the transistor Q1 is turned off such that an output signal is no longer available on lead h to refire the rectifier CR3. Transistor Q2 is, therefore, turned off and after a brief charging of capacitor C3 and discharging of capcitor C2, the voltage across its resistor R16 is removed. When this happens, the ,diode CR4 conducts and the capacitor C4 is shortly discharged through the diode and resistor R16. Transistor Q3 stops conducting and causes discharge of the capacitor C so that the transistor O4 is turned off. This removes the alarm signal on lead k and the rectifier CR6 is then turned off to de-energize the alarm devices. It may be noted that although the rectifier CR3 is turned off and on according to the rectified pulsating signal on lead a during a delay timing period, the charging of capacitor C4 is essentially undisturbed by the extremely short off moments.

Illustrative types of components and values of elements in the

functional circuits

38 and 40 are as follows.

CR3 PIV C1068 Rll 2.2 kilohms CR4 IN695 R12 3.3 kilohms CR5 IN4748 R13 3.3 kilohms R14 47 ohms Q2 2N3638 R15 1.2 kilohms Q3 2N34l5 R16 560 ohms Q4 2N3638 R17 1.8 megohms R18 3.6 megohms C2 25 mfd. R19 I20 kilohms C3 40 mfd. R20 82 kilohms C4 mfd. R21 8.2 kilohms C5 200 mfd. R22 l2 kilohms R23 220 ohms R24 l.8 kilohms In the exemplary failure warning system 28 having the characteristics and circuitry as described above, a momentary power failure or a transitory low voltage condition lasting approximately one second or less during a delay timing cycle such as when defrosting will not cause automatic reset of the timing cycle, although it may cause this cycle to extend its duration about a minute longer than that set by the rheostat R18. An extended power failure or low voltage condition lasting, for example, about ten seconds or more will cause the timing cycle to reset automatically and start again from its zero time point when the power or voltage returns to normal. Of course, in the event that power to the system 28 fails'during the night when a store is unattended or the systems power is inadvertently cut off during closing of the store, it is apparent that the system should desirably include a power failure warning circuit. It is further desirable that, in addition to including an internal alarm device, external alarm provisions be made.

Functional circuit 44 shown in FIG. 2B is a power failure warning or alarm circuit. Lead a is connected to the positive terminal of a 7.5-volt (alkaline) battery 62 through a l2-volt Zener diode CR7, an oppositely oriented lO-volt Zener diode CR8 and a resistor R26 which are connected in series and constitute a trickle charger for the battery. The negative terminal of the battery 62 is connected to lead g which can be connected to lead fwhen control switch 48 (FIG. 2A) is closed. The leaffis connected to the food case ground 64 which normally extends throughout the store. The lead e is also connected to the case ground 64. Lead b is connected to one side of capacitor C6 by series resistor R27 and diode CR9. The other side of capacitor C6 is connected to lead e, and the junction between diode CR9 and the capacitor is connected to the emitter of transistor Q5 which is connected in a voltage analyser stage.

The positive terminal of battery 62 is connected to the collector of transistor Q5 by resistor R28, and the emitter of the transistor is connected to lead e by resistor R29. The battery 62 positive terminal is also connected to the lead e by series resistors R and R31.

The junction between the resistors R30 and R31 is connected by a resistor R32 to the base of the transistor 05. The transistor Q5 base is connected to lead e by capacitor C7. Values of the circuit elements are preferably selected so that the capacitor C6 is charged or discharged considerably faster than the capacitor C7. The collector of transistor O5 is connected by resistor R33 to the base of transistor Q6 which functions as a solid state switch. The positive terminal of battery 62 is connected by resistor R34 to the emitter of transistor Q6, the collector of which is connected by resistor R35 to lead e. A solid state audible alarm 66 which can be a low current, ceramic magnetostrictive device (Mallory SC628, for example) is connected across the resistor R35. The collector of the transistor O6 is connected by a diode CR10 to the junction between the resistor R25 and the upper terminal of the external alarm connector 60, to provide a power failure alarm signal to such terminal. The resistor R25 and its connected circuitry present an insignificant drain or load on the power failure alarm signal.

When the system 28 is turned on by closing the control switch 48, the leads f and g are connected together. The battery 62 is maintained in a constant, fully charged condition by trickle charging with the rectified pulsating signal from lead a. With 24 volts (r.m.s.) on lead a, the (open circuit) charging voltage to battery 62 is about l0 volts which is suitable for charging the battery. The capacitor C6 is charged by the regulated signal on lead b well before the capacitor C7 is charged. Power failure resulting in the complete loss or at least a predetermined loss of voltage on lead b will cause the rapid discharge of the capacitor C6 to a condition such that the transistor Q5 conducts. The voltage on the base of transistor Q6 is reduced to an extent that the transistor conducts and battery 62 power is applied to the audible alarm 66 and through diode CR10 to any external alarm connected between the upper terminal of connector 60 and case ground 64. Thus, the power failure alarm circuit continuously samples the regulated signal on lead b and maintains switch transistors Q6 off so long as this regulated signal is present. Disappearance or at least a predetermined loss (as may be established by selected analyser transistor Q5 circuit parameters) of the regulated signal causes the transistor Q6 to conduct and apply power from the battery to the audible alarm 66 and any external alarm.

Illustrative types of components and values of elements in the functional circuit 44 are as follows.

CR7 IN4742 R26 300 ohms CR8 IN4740 R27 1.2 kilohms CR9 IN695 R28 l.2 kilohms CR10 IOD2 R29 560 ohms R30 6.8 kilohms Q5 2N34|S R31 IOOO ohms 06 2N3638 R32 3.3 kilohms R33 3.3 kilohms C6 40 mfd. R34 47 ohms C7 200 mfd. R35 2.2 kilohms Operationally, after the cooling failure warning system 28 has been properly installed with its sensors 12a, 12b and mounted correctly in a food case, control switch 48 is turned on (power lamp 22 energized) and the system allowed to stabilize for several minutes. After ensuring that the food case being protected is not in a defrost cycle, the potentiometer R4 temperature adjustment (setpoint). at the bottom of the metal case 14 (FIG. 1) is rotated by an inserted screwdriver until the left defrost or caution lamp 24 just lights. At this point, the system 28 has been adjusted to an alarm temperature equal to the temperature at which the food case is operating. To raise the alarm temperature to some point above the operating temperature of the food case, the potentiometer R4 adjustment is now rotated in the opposite direction (which extinguishes the defrost lamp 24) for a selected number of divisions on the scale 68 (FIG. 2A).

Each division of the scale 68 represents, for example, a 5 F increase in the alarm temperature setting. Thus, to set an alarm temperature F above the operating temperature of the food case, the potentiometer R4 adjustment is rotated until the defrost lamp 24 just turns on and then the adjustment is reversed in rotation direction for three division spaces on the scale 68. With adjustment of the alarm complete, and knowing the duration of the defrost cycle, the calibrated delay rheostat R18 adjustment at the bottom of the metal case 14 is adjusted to a setting on the calibrated scale 70 (FIG. 2B) for the desired delay. All adjustments of the system 28 are now complete and the system is ready for service.

It should be apparent from the foregoing description of an exemplary embodiment of this invention that it is susceptible of modification in its detail construction and arrangement of parts without departing from the principles involved or sacrificing any of its advantages. It is, therefore, to be understood that the particular embodiment of the invention described above and shown in the drawings is merely illustrative of, and not restrictive on, the broad invention and that the invention is claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims.

I claim:

l. A cooling failure warning system for a refrigerated food case and the like, said system comprising:

a source of a rectified, pulsating, supply signal;

temperature sensor means installed in a selected location of said food case, said sensor means being responsively variable in output in accordance with its sensed temperature;

means responsive to said sensor means output and producing a switch signal for a sensor means output corresponding to a sensed temperature of at least a predetermined value higher than operationally normal for said food case;

temperature alarm means;

alarm switch means responsive to said switch signal for applying said supply signal to energize said temperature alarrn means; and

means for delaying said switch signal a predetermined period of time and accordingly the response of said alarm switch means thereto.

2. The invention as defined in claim 1 further comprising means responsive to said sensor means output and producing said switch signal at a sensor means output corresponding to a sensed temperature of at least a predetermined value lower than operationally normal for said food case.

3. The invention as defined in claim 1, further comprising power alarm means, and means responsive to a lossof said supply signal of at least a predetermined amount and producing a power alarm signal for causing energization of said power alarm means.

4. The invention as defined in claim 1 further comprising a source of a regulated signal, and wherein said sensor means is responsively variable in output resistance in accordance with its sensed temperature, and said means responsive to said sensor means output for producing a switch signal includes a reference divider network energized by said regulated signal and having a first output signal obtained from a first selected point thereof, said sensor means being connected to said network to vary said first output signal according to the variation of said sensor means resistance, and amplifier means responsive to said first output signal for producing said switch signal at a sensor means resistance corresponding to a sensed temperature of at least a predetermined value higher than operationally normal for said food case.

5. The invention as defined in claim 4 further comprising timing switch means responsive to said switch signal for initiating production of a timed output signal from said delay means, said alarm switch means being responsive to said timed output signal to apply said supply signal to energize said temperature alarm means.

6. The invention as defined in claim 5 wherein said regulated signal source is supplied by said supply signal source, and further comprising power alarm means, and means responsive to a loss of said regulated signal of at least a predetermined amount and producing a power alarm signal for causing energization of said power alarm means.

7. The invention as defined in claim 5 further comprising means connected to a second selected point of said network to obtain a second output signal therefrom when said sensor means resistance is at least of a predetermined value corresponding to a sensed temperature of at least a predetermined value lower than operationally normal for said food case, said amplifier means being responsive to said second output signal to produce said switch signal.

8. The invention as defined in claim 4 further comprising means connected to a second selected point of said network to obtain a second output signal therefrom when said sensor means resistance is at least of a predetermined value corresponding to a sensed temperature of at least a predetermined value lower than operationally normal for said food case, said amplifier means being responsive to said second output signal to produce said switch signal.

9. The invention as defined in claim 8 further comprising timing switch means responsive to said switch signal for initiating production of a timed output signal from said delay means, said alarm switch means being responsive to said timed output signal to apply said supply signal to energize said temperature alarm means.

10. The invention as defined in claim 9 wherein said regulated signal source is supplied by said supply signal source, and further comprising power alarm means, and means responsive to a loss of said regulated signal of at least a predetermined amount and producing a power alarm signal for causing energization of said power alarm means.

11. A cooling failure warning system for a refrigerated food case and the like, said system comprising:

a source of electric power, and electric signaling means connected to said source;

temperature sensor means connected to said signaling means and adapted to be installed in a selected location in a food case to sense the ambient temperature, said sensor means being responsively variable in output in accordance with its sensed temperature;

said signaling means including means connected to said sensor means and responsive thereto to produce a switch signal for a sensor means output corresponding to a sensed temperature of at least a predetermined value higher than operationally normal for said food case;

adjustable timing means connected to said switch signal producing means for delaying transmission of said switch signal for a predetermined period of time;

temperature alarm means; and

alarm switch means connected to said timing means to receive said switch signal upon completion of 5 the timing delay and responsive to said switch signal to energize said temperature alarm means.

12. The invention as defined in claim 11 wherein said sensor means comprises a plurality of discrete sensors adapted to be arranged in spaced relation and connected in series to the switch signal producing means;

the latter being responsive to an overtemperature indication from any one of said sensors to produce a switch signal.

13. The invention as defined in claim 11 where the switch signal producing means is responsive to an open circuit in the sensor means to produce a switch signal.

14. The invention as defined in claim 11 further comprising power alarm means;

and means responsive to a loss of power of at least a predetermined amount in said signaling means and producing a power alarm signal for causing energization of said power alarm means.

Claims

1. A cooling failure warning system for a refrigerated food case and the like, said system comprising: a source of a rectified, pulsating, supply signal; temperature sensor means installed in a selected location of said food case, said sensor means being responsively variable in output in accordance with its sensed temperature; means responsive to said sensor means output and producing a switch signal for a sensor means output corresponding to a sensed temperature of at least a predetermined value higher than operationally normal for said food case; temperature alarm means; alarm switch means responsive to said switch signal for applying said supply signal to energize said temperature alarm means; and means for delaying said switch signal a predetermined period of time and accordingly the response of said alarm switch means thereto.

3. The invention as defined in claim 1, further comprising power alarm means, and means responsive to a loss of said supply signal of at least a predetermined amount and producing a power alarm signal for causing energization of said power alarm means.

11. A cooling failure warning system for a refrigerated food case and the like, said system comprising: a source of electric power, and electric signaling means connected to said source; temperature sensor means connected to said signaling means and adapted to be installed in a selected location in a food case to sense the ambient temperature, said sensor means being responsively variable in output in accordance with its sensed temperature; said signaling means including means connected to said sensor means and responsive thereto to produce a switch signal for a sensor means output corresponding to a sensed temperature of at least a predetermined value higher than operationally normal for said food case; adjustable timing means connected to said switch signal producing means for delaying transmission of said switch signal for a predetermined period of time; temperature alarm means; and alarm switch means connected to said timing means to receive said switch signal upon completion of the timing delay and responsive to said switch signal to energize said temperature alarm means.

12. The invention as defined in claim 11 wherein said sensor means comprises a plurality of discrete sensors adapted to be arranged in spaced relation and connected in series to the switch signal producing means; the latter being responsive to an overtemperature indication from any one of said sensors to produce a switch signal.

14. The invention as defined in claim 11 further comprising power alarm means; and means responsive to a loss of power of at least a predetermined amount in said signaling means and producing a power alarm signal for causing energization of said power alarm means.