CA1132679A - Refrigeration system control method and apparatus - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A refrigeration system contains a common compres-sor supplying refrigerant to a plurality of evaporators that are refrigerated and defrosted independently of one another. Individual refrigeration/defrost controls are pro-vided in solid state form for the respective evaporators, and the individual controls are connected with a master control that prevents all of the evaporators from being defrosted at one time. The master control includes a digi-tal time clock providing time signals to each of the indivi-dual refrigeration/defrost controls, and each of the indivi-dual controls can initiate a defrost operation for its respective evaporator on either a timed or demand basis.
The master control includes a scanner that interrogates the individual controls in a special manner to initiate defros-ting of the units in order of priority. The master control permits an individual defrost control for a selected evapo-rator to be tested in a timed mode by substantially increa-sing the speed of the time clock while operation of the remaining defrost controls is inhibited.

Description

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B~CKGROUND OF THE INVENTION
The present invention relates to the method and apparatus for controlling defrost and refrigeration opera-tions in a refrigeration system having a plurality of evaporators. More particularly, the invention relates to controls allowing the evaporators to be defrosted and re-frigerated independently and without overloading the sys-tem. The invention has utility in refrigeration systems having hot gas or other defrosting equipment.
It is customary in large refrigeration systems such as found in food stores or supply houses to utilize an integrated refrigeration system for a plurality of refrigeration units. A common compressor and condenser supply all of the refrigerant needed by the evaporators in the various units. However a certain degree of independen-cy of the units is required because of the different demands imposed on the units. For example, in a food store, a re-frigeration cabinet containing ice cream or frozen foods is normalIy held at approximately -20F and imposes far more strin-gent demands on the refrigeration system than a milk cabi-net or veget~ble tray that operates in the vicinity of +40F.
Furthermore, temperature and humidity conditions and the frequency with which the cabinets are opened and closed at various times of the day also affec~ the refrigeration pro-cess. Because of the variations in demand, the accumulation of ice and frost on different evaporator coils in the system varies widely, and independent defrosting and refrigeration controls are needed to keep the evaporators and the system operating efficiently. In this respect, reference to an evaporator is intended to refer to one or more evaporator coils connected in parallel or series to be refrigerated '..

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1~ z&~7q -'' and defrosted in commo ¦ In large con~ercial refrigeration systems, defrostin~
is -frequently accomplished by transmitting hot refrigerant in Igaseous form d;rectly through the evaporators to melt the ¦accumulated ice and frost. Such hot gas defrosting s~stems may 'reduce the available refrigerant for cooling purposes to an inadequate level for other evaporators in the system unless control~
is e~ercised over the number of evaporators that can be placed in the de-frosting mode at any one time. Also ~vith other defrosting ~devices such as electrical heaters connected to the evaporator coils, the number of evaporators defrosted at any given time must be controlled to prevent power overloads and undue demands on the refrigeration equipment.
~5 I Accordingly, it is customary in refrigeration systems ~having multiple evaporators to limit the number of evaporator~ that are placed in the defrosting mode at any given time - Such limita-. Itions can be imposed by scheduling the defros$ operations -for particular times of day, ho~Yever, timed defrosting may not be satis~actory where demands on the refrigeration system are ¦irregular and incapable o~ prediction. In these cases, a demand ~defrost system is generally preferred. In a demand system, frost sensors associated with the evaporators provide signals ~Yhen accumulated frost and ice has reached a given level. In the Iabsence o-f further control, however, it is clear that a demand syDtem could place nlOre than one and possihly all of the i, .
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evaporators in defrost at one time. To prevent the possi-bility, control systems, have been devised such as disclo-sed in U. S. Patents 3,894,404 and 4,151,722. Tn U. S.
Patent 4,151,722, scanning means are provided to periodi-cally interrogate or examine the frost sensors in a prede-fined sequence. When one of the sensors indicates that its corresponding evaporator is in need of defrost, scanning is halted until defrost of the evaporator is complete. A
certain priority can be developed by increasing the fre-quency that one evaporator is scanned relative to theothers. Thus, for example, a high priority evaporator can be scanned twice as often as the other evaporators to in-crease the probability of detecting the need for defrost at an earlier point in time.
It is an object of the present invention to provide a defrost and refrigeration system which allows a plurality of evaporators to be controlled independently of one another and which constitutes an improvement ov~r the prior art systems.

SUM;l~RY OF THE INVENTION
In accordance with one aspect of the present in-vention there is provided a control apparatus with a refrigeration system having a plurality of evaporators and defrosting equipment connected to defrost each of the eva-porators independently of the others, comprising timing sig-nal generating means having an adjustable speed for produ-cing at an adjustable rate timing signals from which the defrosting of individual evapoxators are scheduled, control-led switching means connected between the timing signal generating means and the defrosting equipment for actuating in response to the timing signals individual portions of the equipment associated with the respective evaporators and thereby switching the corresponding evaporators into a Z67~ -defrosting mode when a timing signal for said evaporator is produced, and testing means connected in controlled relationship with the timing signal generating means for increasing the rate at which the timing signals are gene-rated and for thereby switching the evaporators into their defrost modes at accelerated points of time.
In accordance with a further aspect of the pre-sent invention there is provided a method of testing the defrost controls in a refrigeration system in which a plu-rality of evaporators are scheduled to be defrosted at dif-ferent times in response to defrost signals generated by a time clock, comprising driving the time clock at an accele-rated rate at least until the clock reaches a time when a given evaporator is scheduled for defrosting and a defrost signal for the given evaparator is generated, and determi-ning if the defrost signal for the given evaporator is generated at the scheduled time.
BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic diagram illustrating the overall refrigeration system having a plurality of evapo-rators with individual refrigeration/defrost controls for each evaporator.
Fig. 2 is an electrical diagram illustrating the various components in the master control for the refrigera-tion system.
Fig. 3 is a diagram of a digital time clock and decoders which generate time signals for the refrigeration system in one embodiment.

Fig. 4 illustrates in greater detail one of the numeral elements utili~ed in the digital display of the time clock in Fig. 3.
Fig. 5 is a block diagram illustrating the ~ 3~6t~

functional elements of an individual refrigeration/defrost control and connections with the master control of Figure 2.
Fig. 6 is divided into Figs. 6A and 6~ as shown, and constitutes an electrical diagram illustrating a solid state embodiment of the individual refrigeration/defrost control in Fig. 5.
Fig. 7 is an electrical schematic illustrating the power supply for the digital time clock and the defrost controls.

Fig. 1 illustrates the components of a refrigera-tion system, generally designated 10, embodying the present invention. A compressor 12 delivers hot, gaseous refrige-rant to a cond~nser 14 where heat is transferred to the am- `
bient air with the aid of a cooling fan 16. Cooled and condensed refrigerant is directed in a conduit 18 from the condenser to evaporators 30, 32, 34 by refrigeration and de-frost control valves 20, 22, 24 respectively when the valves are individually set in the refrigeration mode. When the valves are set in a defrost mode, the compressor 12 supplies hot refrigerant in gaseous form to the respective valves and associated evaporators through the conduit 36. The conduit 37 returns the refrigerant to the compressor. A more detai-led description and explanation o the refrigeration and defrost valves may be had from the above reference U. S.
Patent 4,151,722.
The refrigeration and defrost operations or cycles for the plurality ~f evaporators 30, 32, 34 are controlled by a master control 38 associated with all of the valves and evaporators, and individual refrigeration/defrost controls 40~ 42, 44 connected separately and independently with the -respective valves and evaporators. Thus, the individual control 40 regulates the flow - -.

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<~ i ~ l of condensed or hot re~rigerant tllrough the valves 20 and ¦ evaporator 30, the individ~lal control ~2 regulates the ~low o~
condensed or hot refrigerant through the valves 22 and evaporator 1 32, and the individual control ~ regula-tcs the flow of re~rig-I exant through the valves 24 and evaporator 34.
From the above description, it will be understood that ¦
the'refrigeratlon system 10 has a hot ~as defrosting system to i defrost the evaporators 30, 327 34 individually. However, the ¦ present invention is not limited to a hot gas defrost system and ! other types of de~xosting equipment s~ch as electrical heaters can be connected respectively with the evaporators to permit ¦ independent defrosting'of the separate evaporators.
¦ The master control 38 in Fig. 1 i5 illustrated in a I solid state embodiment in Fig. 2. Among other ~-lnctions, the ' I master control provides time sigllals that allow the individual ¦ refrigeration/de~rost controls to operate on a timed basis. The control 38 also provides the mealls by ~vhich testing of the indi--¦ ~idual controls can be accomplished, and includes a unique , scanning device that allows the evaporators to be interrogated' , concerning the need for de~rosting in order o~ priority.

, ' IME DECODING
' In Fig. 2, the basic source of time signals in the mas~er contr~l 38 is the digital time clock 50. ~Yhile the ~ digital clock is not essential to many aspects o~ the present 2s 11 inven ion, it does provide e unique means by which time signals 1, ' ' i, I!

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j can be generated. In one form, the digital clock is a 24-hour clock having a digital display and by means of a two-hour decoder ¦ 52 and a 24-houl decoder 54, a time signal is produced every half ¦ hour. Thus, any one of the evapor~tors in the re~rigeration ¦-I system can be scheduled in the timed mode.to defrost at any hour or half hour of the day. Although an evaporator may be scheduled to defrost at a particular time of day, such defrosting ~vill not necessarily occur due to the defrosting of higher priority evaporators as described in grea-tex detail below.
In ~der to more fully understand the operation of the .. I time clock 50 and decoders 52 and 54, reference is made to Figs. -3 and 4. The digi-tal clock 50 has counter and control circuitry 5 which is enexgized by 60 cycle a.c. power. The circuitry utiliz- 1 . ing the 60 cycle power as a timing reference computes time which I :
is pre~erably output in BCD form to four 7-segment decoders 60, . 1 62, 64, and 66. The 7-segment decoders are associated respective-. I ly with numeral elements 70, 72, 74, and 76 that ~orm the digits ........ ¦ o~ the time clock display and each decoder generates one of the ! time digits. For example, the decoder 60 generates the tens-hour .20 I digit, the decoder 62 generates the ones-hour digit., the decoder , 64 generates the tens-minute digit and the decoder 66 generates the ones-minute digit. For the purpose of discussion, it will I be assumed that the digital clock is a 24-hour clock such as model¦
.: I ~i~1002 digital clock module manufactured by National Semiconductor .25 Corporation, Santa Clara, California. Each numeral element 70, .; ¦ 72, 74, and 76 has the same construction shown ill Fig. 4 and com-~ prises a circuit board 78 havin~ seven liglt emitting diodes , -S-I I
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t (LED)s or segments A, B, C, D, E, F, and G arr~n~ed in a figure-S pattern. Any decimal intcger Irom 0 to 9 can be illustrated in the pattern by illuminating selected segments in ¦ combinatio~, and it ~rill be assumed that the segments are con-j stantly energized when illu3ninated to form a particular integer.
By energizing selected s-egments in various combinations and patterns in each of the numeral elcments, a visual presentation of the time is manifested. The display changes everyrninute in accordance with the data produced by the counter circuitry ~
Since the excitation of the segments and the corres-ponding illumina-tion is peculiar to a given time, a time signal can be generated by determining which sevments are illuminàted at that particular time, then moni-toring the energi~ation or illumination o~ the segments and producing the time si~nal when the particular combination or code of illuminated segn~ents is Aetected. It is not essential that all illuminated segments ¦ be used to establish an unambi~uous code. Only some of the I illuminated se~ments may be uniquely associated with a particular ¦ time. When signals are desired at spaced times thxoughout a day,~
I particularly evenl~ spaced times when a digital integer is ¦ r~peated, it is frequelltly possible to ~e~nelate a time signal from less than all illurminated segments. Furthermole, the non-illumin~
I ated segments or combinations of illuminated and non-illuminated j segments may provide a unique time code. It is also possible ithat the code b~ based UpOll derivative parameters of the digital g_ i 1~326~7S~ , ,.`~ 1. , ., . i `'~' I . , , I
display such as positive-going or negative-going transitiOnS of the segments between the ener~ized and non-energized conditions Accordin~ly, a unique time si~nal generatinD ~n~ans is provided by ! decoders such as the decoder 52 which monitor the energizatiOn I of a digital display and produce signals whell a predetermined I -¦code is detected. By counting or accumulating the time sigllals, further time interval signals can be obtalned.
It can be shown by analysis o tlle illumination patterns¦
I that the B and C segments or LEDs of the tens-minute digit when lapplied to a coincidence gate, such as the AND gate 120 in the decoder 52 of Fig. 2, initiate a positive pulse on the hour and ¦half hour corresponding to a freq-lency of two cycles per hour.
For digital circuitry, such a cyclic rate is very low, but the resolution provided by time signals generated at tllat frequency is ~5 ladequate for selecting defrosting times. The pulse signals are used as clock inputs ~or a solid state "D"-type flip-flop 122 and j a static sllift register 124 which serves as a sequencing and accu- j ¦.~! Imulating means. Both the flip-flop and shift xe~ister respond to Ithe leading edge of the positive pulses, and cause the outputs 80, !0 ¦82, 84, 86 to se~uentially assume a binary l-state or "high" with !each succeeding pulse. Thus, every half hour the outputs chanve to ¦Igenerate a time signal and only one O~ltpUt iS in the l-state or ` ! tuxned on at any given time. One half-hul a~ter the output 86 ; ~,is turned on, the leadillg edge of a subsequent pulse from th2 ~N~
;5 gate 120 causes the sequencing of the output signals to be started .
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¦ again througll the feedback connection ~ith the "D" input of the ¦ ~lip-~lop 122. Thus, -tlle four outpUts 80-86 of the two-hour decoder are tuxned Oll individually and at evenly spaced inter-i vals over a two-hour pexiod. The flip-flop and shift register ¦ ef~ectively count the timing pulses produced by the coincidence ¦ gate 120 so that the outputs of the decoder provide not only time signals but signals representing accumulated time in ha~
hour increments over a two~hour period as illustrated.
At the end o~ a t~Yo-hour period, when the output ~0 is ¦
again turned on, the leading edge o~ a pulse ~rom the output is ¦ transmitted to another "D"-type flip-flop 126 and a shi~t reg-¦ ister 128 which comprise the 24-llour decoder 54. The shift : register 128 is illustrated as a single shift register, but in ~act, could be comprised o~ a plurality o~ shi~t registers connected in series. The operation of the ~lip-~lop 126 and ¦ -.; shift register 12S is basically the same as the ~lip-flop 122 ;~; and sh~t register 124 except that since the clocl; signals are ¦
s j derived from the decoder 52, the outputs 90-112 are turned on J individually in sequence at 2-hour intervals. ~Yith twelve such !
¦ outputs, a time signal is produced ~rom the decoder 54 every ` ¦ 2 hours over a 24-hour period. By applying the time signals from I the outputs o~ both decoders 52 and 54 in various combinations Y; ! to coincidence ga~es, a time signal can be pxoduced at any I hal~ hour of the day over a 2~-hour period.
For purposes o~ setting the shi~t registers 124 and l~S
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; 3i a reset circuit 130 is provided. The leset circuit is basically ¦another decoder connected with the digital clock 50 and is ; Icomprised of a NOR gate 132. ~s indicated, the inputs to the gate 132 are ta~en ~rom the B scgmellt of the ten hour digit, the C segment of the hour digit, the G segment o~ the 10-minute digit and the C segment oP the minute digit. Due to the logic f of the NOR gate, a positive pulse is initiated and applied to the ~lip-~lops 122 and 126 and the shift registers 124 and 128 lonly when none of the identified segments serving as inputs is energized. Thus, the NOR gate fùnctions in respo~se to the i Inon-energization of selected inputs, and it can be shown that ¦ -¦with the identified inputs and associated code, the NOR gate pro-duces a positive one minute pulse at 2:02 witll a 24-hour clock.
~ A second but inconsequential pulse occurs at 2:12. In response `1 15 to the leading edge of the first pulse, the outputs of ^ !decoders 52 and 54 are set independently of clocking pulses and ¦the outputs assume the states correspondlng to the time 2 02.
f~ ISuch setting function is used to s~nchronize the outputs and the ¦time display of the clock a~ter the system is turned on.
~ From the above, it ~ill be understood that the time or ,timing signals for initiatillg defrost operations are derived i-¦from the digital clock 50 by the decoders 52 and 54. Although the ¦
!signals are generated in half hour increments by the exemplified ¦~ Icode, other codes utilizing both ener~ized and non-energized 'segments permit many other time increments and timing si~nals to be obtained.
~hile the digital time clock 50 and decoders 52 and 54 rcpresent a unique means for obtaining time signals, the f t : 3 -12- ~

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; refrigeration system could also oper~te with more conventional -i timing devices providing signals at selected times o~ day.
¦ Also, the illumination o-E numeral segments from which the de-~ codels operate can be derived from timing devices other than I the digital clock. Still further, it is contemplated that -¦ energization of numeral element5 other than the seven segment numerals may be monitored to produce time signals.

:~ TE~T FUNCTIO~
The master control 38 includes components for tes-ting 0 ¦ an individual refrigeration/defrost control for an evaporator. ~i A test ~unctlon is carried out by progran~ing an individual con-¦ trol ~0, 42 or 4~ in a time defrost mode of operation and then driving -the di~italclock at an increased rate until the time is ` ~ reached when the individual control under test is pro~rammed to ` 15 , initiate a defrost cycle. The control is then examined to deter-1~ ¦ mine i~ a de~rost operation has been properly initiated.
In particular, a NOR ga*e 140 has one input terminal ~ that is normally held in the l-state by the power supply and ¦~ a resistor 142 and another input held in the 0-state by the 1I power supply, resistor 136 and digital inverter 138. When a ¦
I' test signa1 as illustrated in the foxm of a negative or "low ¦~ level signal is reccived rom any of the individual defrost - 1 controls ~0, 42 or ~4, the signal switches the output of the NOR gate to its l-state, provided that a defrost signal is not !~ present at the other input terminal of the gate. A defrost ., 11 .
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- signal,also illus-trated as negative si~llal, indicates $hat one of the individual controls and a corrcsponding evaporator is in a defrosting cycle, and inhibits the NOR gate l40 and test function ndex such circu1nst~nces to prevcn-t more 1;11an o11e evaporator fl~.n being placed in a deflosti11g mode at a time. It should be noted ! parenthetically that the oval designations in the dra~vings repre- i : ~ sent conductors that are common to all of the evaporators, and therèfore, the test signal or defrost signal may come from any . I one Or the individual defrost controls 40, 42? ~. A defrost ; lO signal is also applied to a "D" valve 1~4 which reduces the com- ¦
pressor discharge pressure so tl1at hot ~as from -the compressor can be circulated through the evaporators in a hot ~as defrosting ¦
system.
Assuming that a defrost operation is not being carried `15 ¦ out when the test signal is received, the output of the NO~ gate 140 is transmitted through an OR gate 1~6 to ~ast clocking cir-cuitry 1~8 in the digital clock 50, and the digital clock is then , driven at an accelerated rate. For example, the digital time j display is sequenced through one hour in an actual time of one ~0 second. Since the decoders 52 and 5~ respond to the display xather than actual time, the time signals produced by the outputs !
; of the shift xegisters 124 and 128 appear a$ a correspondingly accelerated rate and the programmed time of defrost for a ~ar-¦ ticular evaporator is reachecl in s11ort orc1er. As soon as the 25 j individual control under test xeceives its progra~1ed .time signal, `~ !
-.~ I the control should go illtO the deIxost mode of operation a1~d a .~ defrost signal should be transmittcd from the Ul1it under test to , ,., ~
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the NOR gate 1~0. The NOR ~ate lg0 is then disabled $ogeLher with the ~ast clocking circuitry l~S and tlle digital clock xe- i turns to normal time sequencin~. By observing the digital dis- j ¦ play o~ the clock, the operator conducting the test can determine I i~ the tested control is ~unctioning properly.
¦ As explained in greater detail below wi-th re~pect to the individual defrost controls, the -test operation will continue until it is terminated by the operator. Termination of the test also terminates defrosting o~ the tested evaporator so -that I the de~rost signal disappears and the NOR gate 140 reverts to its initial condltion.
Since the test ~unction drives the digital clock to the time ~hen the tested evaporatox contxol is programmed for ¦ defrost, the termination o~ the test ~unction will normally lS ¦~ leave the digital cloc~ at the wrong time. For this reason, the operator who xan the test should reset the clock to the correc$
time, and ~or this purpose, a ~ast clock setting button 152 and a slow clock setting button 154 are provided. The fast button 1 152 actuates the fast cloc~ing circuitr~ 148 through the O~ gate -~ 2~ ¦ to bring the digital clock approximately to the correct time~
The operator then presses the slow button 154 ~vhich actuates the j slow clocking circuitry 156 to drive the cloc~ at a xate much less than tlle ~ast clocking cixcuitry but sliglltly greater than , real time. The slow button is rcleased ~/hell the corxect time is observed on the digital display.

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It ~ill be noted that whenever the time clock 50 is being set during testing or by either the fast or slow buttons 152 and 154, OR gate 150 produces a clock setting signal. The setting signal is used as described hereinafter to disable or lockout all individual defrost controls other than the one under test. The lockout function is necessary because the decoders 52 and 54 continue to respond to the digital display as the clock is set, and the generated time signals may correspond to the programmed times for which certain evaporators other than the one under test are scheduled to defrost.
Accordingly, testing of the individual defrost controls 40, 42, 44 is performed by driving the time clock at a high rate until the programmed time appears in the digital disp~y.
Clocking stops at that point and a defrost operation is actually carried out until the operator decides to terminate the test. ~-Thereafter, he resets the clock and the timing signals are ; generated in correspondence with the actual time of day.
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SCANNING FUNCTION
As described above, it is desirable in a refrigera-tion system having a plurality of evaporators to limit thenumber of evaporators which can be placed in the defrost mode at any one time in order to minimize power and cooling capacity overloads. It is especially desirable in hot gas defrosting ; systems to limit the number of evaporators in defrost in order to appropriately scale the capacity of the refrigeration com-pressor 12. In ...

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, I . , the present embodiment, only one evaporator is defro5ted at a time but higher limits are certainly feasible. ~ccordingly, the master control of the present invention is provided ~vith a ~ priority scanner 160 ~Yhich produces sequential probing signals on , I the outputs lG2-176. The probing signals are used to interrogate ¦
, the evaporators or the individual controls fox the evaporators in regard to the need for de~rost. In per~orming the interrogation function in one embodiment of the present invention, the probing signals e~ectively serve as ~ating signals and aliow an indivi-¦dual control to initiate defrosting of the associated eVApOratOr I when the need is indicated. I~ this respect, the need is shown to exist by a signal ~rom a ~rost SellSOr connected with an evap- ¦
orator or by a programmed time signal generated by the decoders 52 and 54.
The priority scanner 160 is driven by clocking pulses ~from a clock pulse generator 180. The p~lse generator receives ; jstandard 60 cycle a.c. current and produces a clocking pulse every .
3-75 seconds or 1/16th of a minute. The priority scanner 160 receives the pulses on a clocking input vJhich triggers the outputs 162-176 one at a time and in n-lmbered sequence. One output is l turned off and the next output is turned on with each positive .~ transition of the clocking pulses, and when each o~ the eight ~outputs has been triggered, the sequence is repeated in a cyclic ,fashion. Thus, with eight outputs and clocking pulses every 3.7~ j , 25 ~seconds apart, eight different evaporators associated respectively . iwith the eight outputs can be scanned by the probing signals in a pcriod o~ 30 seconds.
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The priority scanner 160 in one form can be an integrated circuit such as an RCA counter/divider 4022.
The circuit resets and holds the scanner on the highest priority output when a l-state signal is applied to the reset terminal.
Scanning a plurality of evaporators to indentify those in need of defrost is disclosed in U. S. Patents ~,894,40~ and 4,151,722. ~owever, the scanner 160 performs the scanning function on a priority basis by always resuming 0 the scanning function when interrupted with the first pri-ority output 162. Thus, by connecting the most important evaporator with the first priority output and other evapo-rators with the other outputs in order of priority, the more important evaporators and refrigeration cabinets are ~- defrosted before the others.
Such prioritizing of the defrost operations should be distinguished from the prior art systems shown and des-cribed in the referenced U. S. Patent 4,151,722 wherein certain evaporators are interrogated more frequently than other evaporators. In the present system, a definite prior-; ity is assigned to each evaporator to ensure that the highest --~ priorit~ evaporators will be defrosted first. Furthermore, the order of priorities is observed regardless of the stage of the scanning se~uence when scanning is interrupt d.
In the present system, the scanning is interrup-~ ted at several junctures. Since no more than one evaporator ,.: ,- .
is placed in a defrost cycle at a time, the defrost signal applied to the NOR gate 140 is also transmitted through an OR gate 18~ connected with the reset input of the scanner -~
160. Regardless of which .''~;

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I . , ,: , I . , evaporator is producing the de~rost signal, sc~nning is stopped I and ceases as long as the defrost signal holds the output o~ the ¦ 0~ gate in the l-state. ~hen the defrost cycle terminates and the defrost signal is removed from the OR gate 182, the scanning function xesumes with the ~irst priority output 162 either imme- ¦
diately or, if a switch lS8 is closed, a~ter'a short delay ¦established by a delay timer 190. ~Yith the switch 188 closed, ~" the timer responds through a capacitor 192 to termination of the defrost signal and transmits a delay signal through OR gate 182 ' 10 which delays th'e resumption o~ scanning and allows the system to ~" recover from the previous defrost cycle and balance out in pre-para$ion ~or the ne~t cycle. Thus, if de~rost o~ the evaporator connected with the fourth priority output 168 has just been com-pleted and the evaporat~rs connected with the second priority out-put 164 and the sixth priority output 174 are both in need of defrost, the scanning operation first picks up the second priority ¦evaporator rather than the sixth priority evaporator. There~ore, the higher priority evaporators are cIearly given pre~rence.
The priorlty scanner 160 is also reset in several other linstances. When either the ~ast clocking button 152 or the slow ~ Iclocking button 154 is pressed, a triggering signal is applied to : jone o~ the inputs o~ t~e OR gate 182 to reset and hold the ¦scanner until the time clock 50 is set. Thus, with a new time ¦in the display, scannin~ restarts with the highest priority ' ~25 levaporator. It ~Yill also be understood that ~henever one of the individual de~rost controls is'tested, the time clock is set and ~a defrost signal resets and holds the scanner until the test is , I , , .
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3~i7 ¦ terminated. Scanning again resumes ~vith t~ highest priority ~;~ I evaporator. ~dditionally, a fourth inp~lt to the OR gate 182 ~rom !, the t~Yo-hour decoder 52 is moment~rily pulsed by the t~vo-hour decoder 52 through the capacitor 18~ alld rosets the scanner at ;; 5 the end of each two hour interval when the time signals from the 24-hour decoder change. Resetting at this juncture synchronizes 1, the start of scanning with the start of a new timing period. In . this ~ashion, it is possible to schedule some or all of the evaporators fox defrost at a given time of day, for exalllple, 3:00 a.m. When the 3 a.m. signal is generated~ the scanner 160 is I a~utomatically reset and the scheduled evaporators are de~rosted ; j one at a time in order of priority.
Accordingly, the priority scanner 160 interrogates the plurality of the evapola-tors concerning the need for defrost and gives preferance to those evaporators connected with a llighex priority output of the scanner. The scanning function with priority may be utilized when the evaporators are programmed to defrost in either a time mode as described above or in a demand mode where, for example, a plurality of frost sensors simultaneous-~
ly indicate a need for defrost;
INDIVIDUAL DEFROST CO~T~OL
Having described the master control 38 in detail, ' reference is now directed to the individual refrigeration/defrost ,.. ~ , . . .
controls ~0, ~2J 4~. An individ~lal control is provlded for each ¦ ~vapoxator that is to be refrigerated and defrosted indepelldently ',' I - ' I .
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~,f the others. Although three such evaporators and correspond-ing controls have been shown in Fig. 1, any number of evaporators ~ can be integrated in a refrigeration system providing that the - compressor and other components have an appropriately scaled capacity. Since each individual control has the same construc-tion and functions in the same manner, only one such control is described and shown in Figs. 5 and 6.
Fig 5 is a functional diagram of the individual defrost control 40 for the evaporator 30 and illustrates the connections with the master control 38 and other individual controls.
' The basic inputs to the individual control 40 are received by a time and mode selection circuit 200. Time signals are received by the circuit from the two-hour decoder 52 and the 24-hour decoder 54. Scanning signals when desired are also ` applied to the circuitry 200 from the priority scanner 160 and a frost signal may be provided from a frost sensor 202 connected with the evaporator 30 associated with the individual control. ~-The frost sensor may be of the type described in U.S. patent 3,453,837 which provides a signal indicating a need for defrost when the temperature differential of air blown through the ;~
evaporator indicates that defrost is needed. Of course, other types of frost sensors providing a frost signal can be utilized in the present invention with equal facility.
The time and mode selection circuit 200 is designed to allow defrosting to occur either on a timed basis with signals : `

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¦ received from the decoclers ~2 and 54 or a demand basis with a signal received frolm, the sensor 202. The programming of the cir- , ; cuit determines precisely ~vhich mode of operation is employed and ¦ in a preferred embodiment the mode can be s,elected at will. 17hen ~ the priority scanner 160 is utilized to establish priority of -" , de~rosting among several different evaporators, a defrost actuatin~signal ordered on either a timed or demand basis is not trans-mitted by the circuit 200 until a discrete probing signal from the' , i scanner is received. When the defros-t actuating signal is ordered ,, I
~10 I by any means, the selection circuit 200 transmits the signal ,, ¦ through a two hour latch circuit 204, a defrost lockout circuit ¦ 206 and a clock lockout circuit 20S to a defros-t control s~vitch 210. The control switch 210 is preferably a solid state switch ¦ which can be set and reset by di~ferent sig-nals. ~rhen the signal , from the selection circ~itry is received, the contlol s~vitch 210 ¦ actuates a refrigeration valve or valves 212 and a defrost valve or switch 216 through an unlatching circ~itry 214. The valve 212 closes and stops the fclow of liquid refrigerant from the ' ~ ! condenser into the evaporator and thusly terminateS coc>ling of ;Z0 ¦ the evaporator. The refrigeration valve is also connected with ,` I a xefrigeration indicator 21S such as a light that is turned off when the refrigeration valve is closed.
~- I In a hot g~as defrost system, the clefrost valve 216 opens ' ! at substantially the same time that the refrigeratioll valve closes, " I and admits hot gases into the evaporatox in orcler to melt ice and " frost accumulated on the evaporator coils. Nhen the valve 216 .:, . ' ', , I -22- , `
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i opens, a defrost indicator associated with the valve is turned on Since the indicators 218 and 220 are associated only with the evaporator 30 in the group of evaporators defrosted and re-~ ~rigerated by the compressor 12, reference to a display panel or ~ circuit containing the indicators will immediately show what I cycle the evaporator is in.
It should bè understood that the defrost valve 216 in - another embodiment o~ the refrigeration system may be a switchin device which controls the ~low of current in the electrical de-! frost heater connected with the evaporator 30. Thus, the inven-j tion is not limited to the hot gas defrost system but has general applicability to refrigeration systems having a variety of de-I frosting means.
i I If the timed defrost mode has been selected for the I evaporator, the two~hour latch circuitry 204 effectively prevents ¦ the associatcd evaporator rom being defrosted again within the ; I two-hour period in which deIrosting was originally ordered. Since ; I the time for defrosting an evaporator is usually less than two j I hours, it is probable that a programmed time signal ~or the evap-~; 20 I orator will still be present at the input of the selection cir- ¦
cuit 200 when the defrosting cycle ends. Therefore, upon resump-¦ tion of scanning the higher priority evaporators, defrosting of the same evaporator would be repeated without reaching the lower i .
s priority evaporators if the t~o-ho~lr latch circuit were not I employed.

Thc defrost locl~out circuit 206 receives a defrost signal from any of the other evaporators which îs in a defrosting .
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cycle and prevents the evaporator 30 associated with the lockout circuit 206 from also being placed in the defrost mode even if ; I a time or frost signal indicates a need for defrost. Accordingly,I only one evaporator in the re~rigeration sys-tem can be defrosted ¦ at a time in response to a defrost signal.
¦ The clock ~ckout circuitry 208 prevents a defrost opera-j ¦ tion from being initiated by a defrost signal whenever a clock s setting signal ~rom the master control is received. Thus, during ¦ testing of other evaporators in the refriger~tion syste~ the time ¦ clock is driven at an accelerated rate and may reach the pro-grammed time for de-frost of the evaporator 30 connected with ¦ the loc~out circuit 20S before the prograinmed time for defrosting the evaporator ~nder test. The lockout circuit disables the de-¦ frost signal from circLIit 200 and ensures that only the tested ¦ evaporator goes into the defrost mode. The lockout circuit 208 ; I also prevents the individual control 40 from responding to the time signals whenever the time clock is being manually set.
A manual de~rost button 222 is connected with the defrost ., control switch 210 to initiate a defrosting operation independent-ly of the decoders and sensors connected with the selection circuit 200. Since the button has a direct input to the control switch 210, a normal defrosting operation is carried out when the button is pressed regardless of the condition of the latching and ,i I lockout circuits 204, 2061 and 208; therefore, the circuits can --25 I be overridden by the man-lal defrost button and more than one j evaporator may be placed in defrost if necessary.
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The individual control 40 is provided with a tes-t :~; !button 224 to test the operation of the con-trol and the associated , ,portion o~ the ~aster control 38. To perform the test function~ it, is necessary that the time and mode selection circuit 200 be pro- ' 5 ¦grammed in the time mode with the evaporator scheduled to begin ', la defrost operation at a paxticular time. When the test button 224-¦is $hen pressed, a test ~unc-tion signal is transmitted from the individual control ~0 to -the master control where,- as described above in the absence o~ a defrost signal from any o~ the other ~evaporators, a fast clockiI1g signal is generated, and the digital `, Itime cloc~ is driven at an accelerated rate... When the scheduled , -~time of defrost for the individual control 40 is reached, a defros$~
~ !actuating signal emanates from the circult 200 and defrosting starts `; ¦in conventional fashion. -¦
lS I It will be observed in Fig. 5 that the test function sig-~
~ !nal within the individual control 40 is applied to an inhibit cir-,.~ ~cUit 226 interposed between the master control 3~ and the clock lock-¦out circuitry ~0~. The inhibit circuit prevents the clock setting J
,signal generated in the master control 38 from enabling the clock ¦lockout circuit 208~ and thUs as the time clock iS drive~ a$ an - laccelerated speedJ a defrost actuating signal derived ~rom the ~; Idecoders 52 and 54 is transmi tted from the selection circuit 200 to the defrost control s~vitch 210 to initiate the de~rost operation.
In summary, when the test button 224 is pressed, the $ime ,clock 50 is driven at an acoelerated rate until the scileduled time ' for defrost o~ the individual control 40 is reached, and the de- j -¦~rost operation is initiated. Even if -the scheduled ti~nes of the ~ other evaporators 3~ and 44 are traversed, the other individual con-,, . .

,~ jtrols 42 and 44 associated with o ther evap~rators will not initiate;
ide~rost operations due to the clock lockout circuitry in the other individual controls.

When defrost contlol switch 210 is ac-tuated by the , ~ . , .-. .

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de~rost actuating signal, the re~ eration valve 212 is closed and the xefrigeration indicator 21~ is turned o~f. At the same time, the de~rost valve 216 Ol valves ale actuated to admit hot gas to the evaporator or other~Yise apply heat to the ~ evaporator, and the de:Erost indicator 220 is turned on. It will .~ I be understood that the indicators 218and 220 within the individual l ¦ control 40 only re~lect the mode o~ operation o~ the evaporator 30 ¦ associated with the control. Thus, the person rullning the test : ¦ can visually determine ~rom the indicators whether the master I .
..; 10 ¦ control 38 and the individual control 40 are operating properly.
¦- As long as the test button 224 is pressed, the defrost .. operation will continue in its normal fashion. A de~rost signal ... ~rom the control switch 210 is transmi-tted to the defrost lockout , r circuitry 206 as well as the master coutrol 3S and the other in- j . 3 dividual controls 42, 44, etc. ~y holding the test button 224, :- a ~ull de~rost operation can be carried out and then terminated in normal ~ashion as described in greater detail below; hou/evex, i in most instances, the test button 22~ is only held for a brief period of time until the re~rigeration indicator 21~ and defrost j indicator 220 have turned o~ and on respectively. The operator ~ ! has then received all in~ormation necessary to establish that . , . , the controls are properly operating aud at -that point he ~uld . , I release the test button 22~. Upon release, the test ~unction ~ I signal terminates in the inhibit circuitry 22~, the master con-25 I trol 38 and other individual c~ntrols 40, 42. ~t the same time, ', ' ', . ' .
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I 11 3Z~7~ - -.~ ~ a reset signal is transmit-ted from the button to the de~rost con-trol s~vitch 210 whicll resets the re~rigeration valve in the open position and closes the de:erost valve 216 by way of the unlatch ¦ circuitry 21~ The operator observes that the refrigeration indi- !
cator is turned on,-and the de:erost indicator is turned o~f and thereby verifies that tlle evaporator has returned to a refrigera- ~
tion cycle ~ollowingthe test~ The time clock 50 must then be re- ¦
set to the corxect time by mealls of the setting buttons 152, 154 ~ in the master control o~ ~ig. 2.

`~.10 I DEFROST T~MIN~TION
A time or demand defrost cycle, ox a test cycle if the test button is held for the full duration of a de~rost cycle,is I terminatecl in one of three methods. In the first method a thermo- !
I stat 230 ox other sensor on the evaporator 30 associated with the I indivi~lal contlol ~0 sends a defIost terminate signa~ to the ¦ unlatching circuit 214 to cut off the actuating signal for the de~rost valve 216 and allow the valve to close or shut.o~f other heating devices, The thermostat 230 may be attached di.rectly ¦ to the evaporator in order to determine when the evaporator has ¦ re~ched a temperature which will melt acc~mula-ted ice and frost ,., ¦ or othex types o~ sellsol~s which measure the amo~lnt of frost or icc including the frost sensor itself may be utilized to produce !, the termination signal. If a run off jumper 232 is not connected ¦
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~ I as shown, the defxost control switch 210 holds the refr.igeration .~ 25 ¦ valve212 in the closed posi-tion to prev nt ilNmediate circulation o~
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,,- . I , s refrlgerant through the evaporator. At khis time, therefore~ the evaporator is receiving neither heat throu~h the defrost valve 216 nor refrigerant thrcueh the valve 2127 and melted frost and ; I ice is given the opportunity to run off of the evaporator coils.
I At the end of a run-off period, the defrost control !switch receives a defrost terminate signal from a defrost time I llimiter 234. The time limiter in a preferred embodiment is a settable solid state timer which is preset for a speci~ic period lequivalent to the maximum period for a de~rost cycle. The limiter ! is driven by the same pulsed clocking signal which drives the priority scanner 160 in the master control; however, it should - be understood that other types of timers and different clocking ; signals could be used.
The limiter starts its tlming operation with the 5 :'' "~ 15 ,same signal that actuates the refrigeration and de-frost valves ¦212 and 216, and when the preset time period expires a reset ; Isignal is transmitted to the control switch 210 to re-open ! -~¦the refrigeration valve 212~ Thus~ when the run off-jumper 232- is not in place, the defrost valve is closed by the Ithermostat 230 on the evaporator and the defrost control switch ~10 holds the refrigeration valve closed until after 3 the time limiter 234 has run out. The interval bet~veen jclosing of the defrost valve and re-opening of the refri-geration valve allows melted frost to run off the evaporator Icoils before refrigeration is resumed.
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, A second method of terminatin~ the de~rost operation ! occuxs when the run-o~f j~lmper 232 i5 installed. When the defrost texminate signal :Exom the thermostat 230 unlatches the circuitry 214 and closes -the defrost valve 216, the de~rost termina-te signal~
is also transmitted directly to the control s~Yitch 210 and the refrigeration valve 212 is opened at the same time. ThUS, there is no run-off period With the jumper 232 installed, and re~rigera-tion o~ the evaporator begins immediately upon closing o~ the ¦ de~rost valve.
~10 I A third method o~ terminating defrost occurs when the !
de~rost thermos-tat 230 is disconnected, oX not provided in the system, or the time limiter runs out be~ore the thermostat sends ¦ a terminate signal. Under such circumstances; the de~rost time limiter 234 rUn~ its ~Ull preset time and therea~ter resets the ~15 I control switch 210. ThUS, at the end of the timecl period, the ,~
I de~rost valve216 is closed and the re~rigeration valve 212 opens ! ~ ~:
¦ to begin a re~rigeration cycle.
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AL~RM SYSTEM
! . A tempexature rise thermostat 2~0 connected with the ¦ evaporator 30 and the individual control ~0 is provi~ed to detect , abllormal increases in the evaporator temperature that arise from : a ~ailure of the re~rigeration system. The thermostat is con-¦' nected thiough an alarm locl~out delay circuit 2~2 to an alarm ! indicator 244 within the indiviclual control 40. The alal~ ¦
! indicator is also connected with a co~mon alarm an~ nciator 246 I .

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j~ 7 : 11 in the master control 38. If an abllorrnal and un~nticipated rise I in temperature occurs in the evaporator 30, the thermostat 40 triggers the alarm indicator2 ~ to identify the evaporator as ¦ not properly ~unctioning. The alarm annunciator 2~6 which is common to all of the evaporators in the re~rigeration system is also sounded.
- Since the defrosting operation raises the temperature ¦ of the evaporator 30 well above the temperature that triggers the alarm signal, it is necessary to lock out the alarm system '10 during a de~rost cycle and fox a limited period thereafter while ¦ -the temperature of the evaporator is lo~vered to its noxmal refrig-eration level. The alarm lockout delay circuit 242 thus receives !
an actuating signal from the de~rost control switch 210 as soon I as the de~rost cycle is initiated. In one form, the delay cir-i c~it is a solid state -timer driven by the common clocIiin~ pulses , ¦ applied to the time limitcr 23~ and the priority scannex 160.
¦ The delay circuit may be an adjustable solid state co~lnter which ; ! allows the loc~out period followiIlg defrost -to be selected.
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SOLID STATE E~IBODI~IENT ¦
I Fig. 6 illustrates a solid state em~odiment o~ the individual control 40 described in ~ig. 5 and the interconnections with the master control 38.
The time and mode selection circuitry 200 in Fig. 6 ~ is comprised o~ a plurality of patcll circuits or selector ;~5 ' switches 250, 252, 254, 256, 25~, an OR g~te 260 and a control ~ ~ gate 262. The switches receive timc si~nals from the decotlers ~ '~

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' ' 52 and 54, frost signals from the sensor 202 and discrete probing ¦¦ signals from the scanner 160 in the m~ster control. The switches 250, 252, 25~, and 256 have input contacts which are connected with the twelve output texminals 90-112 of the 24-hour decoder 54 ¦as shown and can be set to select one Ol more time signals for -.
j programming defrosting of the evaporator 30 ~Yhen a timed defrost mode is desired. Thus, the evaporator can be set to deflost at more than one time pe~ day. If a dernand mode is desired rather ll than a timed mode, each of the switches 250, 252 and 25~ is - 10 . connected to ground and the switch 256 is set on the contact connected with the frost sensor 202 to receive frost signals.
, The switch 258 has contacts connected respectively with ~
the outputs 80-86 of the two-hour decoder 52 as well as one of thei outputs of the priority scanner 160 in Fig. 2. It should be lS j understood that the priority of the evaporator 30 is established ¦ by the output of the scanner connected with the input ter~inal I of switch 258. If it is not desired to scan the evaporator 30 ¦ and control 40 at all, then greater resolution of the programmed I de~xost time may be had by connecting *he switcll 258 with one of i20 i the output t~rminals for the two-hour decoder 52 t ¦ The control gate 262 is illustrated as a three-input ' NAND gate which provides a coincidence function. One of the i inputs is connected with the OR ~ate 260, and receives time ~ , sigtnals or ~rost signals from the selector switches 250-256.
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j ~ second o~ the inputs is connectecl ~;ith the selcctor s~itch ¦ 258 and receives other time signals or pro~ing signals. The t ,~ ' ~ , -31-~' ' I
, ! ll~Z~79 ¦, third input is normally held in the binary l-state or enabling ' condition b~ the po~er supply and resistor 136 (Fig. 2) in the t mastex contxol, but is placed in the disabling condition or binary 0-state by a tlefxost signal from any one of the othex evaporatoxs 32, 34 in a de-rost cycle. Coincidence o~ the time, frost or probing signal.s on the first and second inputs of ¦ control gate 262 when the enabling signal is present on the third input causes a de~rost ac-tuating signal to be transmitted by the gate through a NAND gate 26~ to -the de~rost control switch !
210. A disabling deirost signal on the third input.locks out : ! opexation of the control gate so that any oF the timing, probing¦ or frost sensor signals received while anotler evaporator is in a defrost cycle has no effect upon the control ~0. Thus, the ! control gate performs the ~unction o~ the defrost lockout cir-~ cuit 206.
: I The deFrost ac~uating signal is transmit-ted through a 2-hour latch circuit co~nprised of the N~ND gates 264.and 266.
In a time mode, the actuatin~ signal ~hcn received by the gate : j 26~ changes the ou$put of that gate to a l-sta-te and latches the I .
I output in that state through the NAND gate 266 until the time ~ I signal;~rom the OR ~ate 2~0 ~isappears at the end of a two-hour t ;: period. Since a hot gas de~rost operation can usually be com-pleted substantially be~ore a t~:o-hour time signal would ~s-appear from the output o~ OR ga-te 2G0, it would be possible, in the absence o~ the t~o-hour la-tch circuit, tllat a repeat defrost-¦ ing o era-tion woulù occur i~ ed ately upon tll3 term~ination o~
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a first defrostin~ operation. The l~tch circuitry ensures that a defrost operation will not occur because the output of NAN~
' 264 is held in the l~state by the latch circuitry, and the defrost control switch 210 is a solid state switch, such as a I "D" type ~lip-flop ~ctuated only by the positive goln~ transition i of an actuating signal received from the gate 264. Thus, by latching the gate 264 the control s~itch 210 is ef~ectively dis-~` i abled insofar as ~urther time signals are concerned.
; l The manual defrost button 222 is connecte~ directly to , ~ the set texminal o~ the defrost S~Yi tch 210 and sets the switch independently of clock signals or othe1 lockout circuitry. When : -¦ set, a defrost cycle is carried out in a normal manner. , ¦ Whenever the de~rost control switch 210 is actuated ~;i ¦ by either the de~rost button or a clock signal ~rom the control -~ 15 gate 262, ths oppositely phased output terminals Q, Q change ¦! their xespective billary states. The Q-terminal is connected to the defxost valve 216 by way of unlatching circuitry comprised of N~ND gates 270, 272, 274. The output of the N~ND gate 270 , controls actuation of the valve through a resistor 276 connected ..
-20 to the base o~ a PNP power transistor 278. The ~ND gates 272 i I . and 27~ haveinterconllected ~eedback and the outpu-t of the gate f , ~2 is normally in the l-state enabling the ~ate 270. Thus, when , I the Q-terminal o~ the control s~Yi-tch 210 assumes the l-state, ; ~ the gate 270 places the transis-tor 27~ in the conductîYe state, ~25 and actuatcs the defrost valve 216 to apply hcat to the evaporator .,', . Ii i . ~ !
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At the same time the Q terminal of the switch 210 assumes the 0-state and deactuates or closes the refrigerati~
Ivalve 212 throu~h a resistor 280 and NPN transistor 282. Thus, a de~rosting cycle is initiated by the control switch 210 by open- !
ing the de~rost valve and'simultaneously closing the refrigeration valve'. At the same time a defrost lockout signal is produced by the terminal of switch 210 and the signal is transmitted to the master;
i~ control and ot~er individual controls thlough the isolation diode 0 302. ' ' I~ the mode switches 250-258 are in the timed mode, that is, each o~ the switches is in a position responding to a time signal, the control switch 210, rcfrigeration valve 212 and defxost valve 216 are actuated in the same manner as described above when the test button 22~ is pressed and held in a test joperation. Pressing the test button 224 ~rounds the associated ¦input of a NAND gate 290 normally in the l-state due to the power ~
¦supply and resistor 292 and transmits a test signal such'as sho~vn ~ j !through a diode 294 to the ma.ster control 38 and the other indivi-¦
;~0 ~dual controls ~2, 4~ in the xe~rigeration system. At the same jtime, -~orward bias on the NPN transistor 296 through the base ¦
Iresistor 298 is removed which causes the capacitor 300 to discharge - Ithrough resistors 306 and 308.
i The test si~nal causes the time clock 50 in $he master ¦control to be driven a-t an accelerated rate until the programmed ¦time o~ defrost ~or the control unit ~0 is reached. A-t this i Ipoint, the control switch 210 is actuated to initiate a defrost jcycle and produces a de~rost lockout si~nal ~rom the Q output ' -3~-J 1~3~6~
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! which signal is tlansmitted to the master control and other ¦ individual controls 42, 44 through the isola-tion diode 302. Driv-: ! ing the time cloc~ at the accelerated rate then ceases but the ~ defrost cycle initiated by the clocl~ continues until the test ~' 5 1~ button 224 is released.
hen the test button 224 is released, ground is res~ored to the capacitor 300 throu~h the transistor 296 which alsc~ lower's the input termina'l of N~ND gate 304 momentarily to the 0-state while the capacitor 300 xecharges. The NAND gate 304 is momentar I ily actuated which pulses the reset terminal o:E the control I switch 210 to reset the s~vitch and the valve 212 and 216 for a ¦ refrigeration cycle. Thus, the test function terminates as soon a the test button 224 is released. ' ' The N~ND gate 290 serves khe -function o~ the clock lockl-' ` 15 I out circuit 208 in Fig. 5 when the other individual evaporator con ~ 'trols 42, 44 are tested and inhibits actuation of the control ¦ switch 210 in the event that programmed time'signals are recei~ed.
' I For example, when a test button in the indi~idual control 42 is '` t actuated ancl the digital time cloc~ begins running a* an acceler-, ~ ated rate, the programmed time for individual control 40 could ' be reached be~ore the programmed time for individual control 42.
¦ In this case, when the progra~ned time signal in control 40 is transmitted through the control gate 262 to the clocking terminal' ~ j T of the control switeh 210, the D or data terminal of the ... ,. I
1 s~Yitch is at the 0-state clue to the cloc~ setting signal applied , - I to the NAND gate 290. The binary state oI the data terminal is transfe red to the Q terminal when the clocliing si~nnl is recei~e~

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¦' by the T input. Thus, no change in the state o~ the Q and Q
outputs occurs even thou~h a clocking signal is received by the switch, when some othex evaporatox is tested.
I The NAND gate 290 also per~orms the same lockout ¦ unction whenever the di~ital time clock 50 is manually set.
However, the NAND gate 290 does not disable the control switch '' 210-when the test button 224 is actuated because the test signal is applied to the one terminal of the NAND gate 290 normally in the l-state. Therefore, the gate 290 performs the operation of ¦ -I the inhibit circuitry 226 in Fig. 5.
~` . j To terminate the de~rost operation wlth the aid of the ¦ de~rost terminate thermostat 230, a 0-state signal is transmit$ed~
froin the thermostat to the N~ND gate 27~ which in conjunction with the NAND gate 272 ~unctions as a bi-stable ~lip-~lop. The 0-stat~
I~ signal causes the OutpLIts o~ gates 272 and 274 ~nd NA~D gate 270 j to chan~e and render transistor 27S nonconductive. The de~rost ~alve 216 consequently closes. Sillce the ~lip-~lop formed by -~ ¦ gates 272 and 274 has no control over the re~rigeration valYe212 "
,, , the valve xemains closed assuming that the run o~f jumper 232 is ,~ 20 ! not installed. During the period in which both valves 212 and ¦ 216 are clo,sed, melted ice and ~rost is allowed to drip o~i the e~aporator coîls.
, It will be observed that the Q output of control switch 210 is connected to the reset terminal o~ time limitex 234. The .~ ~

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. i li i limiter incl-ldes a resettable bin~ry countel 310 driven by the ~' ¦¦ clocking signals from tlle ~enerator 180 in Fig. 2. The Q output of the control switch 210 holds the counter at its zero count Il until the de~ro~t valve 216 is opened, and the re~rigeratiOn 5 li valve is closed. Clockillg pulses drive the binary counter throu~h-out the defrosting operation to a predetermined count or l j time which is adjusted or preset by a patch circuit 312 bet~een .~ I the counter 310 and a three-input coincidence gate 3i4 in the ¦ limiter~ The patch cixcuit alld coincidence gate ef~ectively form 10 !~ a time decoder ~vhich produces a termination signal at the end of a predetermined maximum deIrost period. The coincidence signal activates the NAND gate 30~ and causes the control switch 210 to ¦I be reset to initial conditions ~hich xenders transistor 282 ¦
:~ . j conductive and opens the r~frigeration valve.212. Thus, between I 1 lS ! the time that the defrost terminate signal closes the de~rost 1,.
valve 216 and the time that the counter 234 runs out, melted ice ij and frost fI'Om the evaporator coils is pexmitted to run o~f. ¦
¦~ Once the refri~er~tion valve lS opened, condensed re~rieerant s I

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i de~ered to the evaporator 30 to l~csume the r~frigelation pro-¦ cess.
! The second method o~ termillclting the defrost operation ¦ is carried out when the run of~ jumper 232 is installed as shown I in phantom. With the jumper installed, the deIrost terminate ¦ signal actuates not only the unlatching circuit and deFrost valve 216 but also the reset gate 304. The control switch 210 is then jreset and the defxost valve ~6 is closed through NAND gate 270 j simultaneously with -the opening o~ the reErigeration valve 212.-~ No run off period is permitted. - ¦
The third method of terminating the de~rost operation is carried out wi-thout the aid of the thermostat 230 either be-cause the thermostat is not included in the system or because ':".' the time limiter 23 is selected to actuate the gate 304 ~nd reset the control switch 210 before the de~rost terminate signal ¦ from the thelmostat is produced. As soon as the s~itch 210 is ¦ reset, the refrigelation valvc and defrost valve are opened j and closed respectively. Thus, again, there is no run off.
~ The alarm lockout and delay circuitry ~42 in Fig. 5 j is comprised o~ an OR gate 320 connected with the control s~itch 210 and the temperature-rise thermostat 240, a binary counter 32Z
and another t'D" type flip-flop switch 324. During a refrigeratio~
cycle, *he temperature rise thermostat 240 normally permits a binary l-state signal from the po-~er supply and resistor 330 ~ 25 i to cxist at one input of the OR gate 320 ~.~hich t.hrough `~ ¦ resistor 3~S blocks conduction oi the PNP transistor 3~G and -~: i ' -3S- !
I
11 !

326'7~
~revents activation of the alarm indicator 244 and co~on ala~n 246. When the evaporator 30 associated with the control 40 is defrosting, a temperature rise would remove the blocking signal and cause an alarm but the alarm indicator is effectively disabled by the delay circuitxy during defrost and a brief period thereafter.
One input of the OR gate 320 is connected to the Q-terminal of the control switch 210. When the Q-terminal assumes the l-state as a defrost operation is started, con-duction of transistor 324 is blocked and thus the alarmindicator 244 will not produce a temperature rise alarm signal nor actuate the common alarm 246.
At the end of a defrost cycle when the refrigeration valve is again opened, the evaporator 30 will still be at an excessively high temperature which could generate the alarm signal. To continue blocking of the alarm signal, the flip-' flop 324 is clocked by the positive-going transition of the Q
'. output of switch 210 when the refrigeration valve 212 is opened.
The flip-flop 324 then transmits a binary l-state signal to OR
gate 320 which signal replaces the blocking signal previously : received from the control switch 210. At the same time, the Q
output of the flip-flop resets the binary timer or counter 322, and the standard clocking pulses count out a predetermined time interval within which the evaporator should have been lowered to its normal refrigeration temperature. As illustrated, the counter ...

39~
.,~
- ':

i ~z~7~
I , ha- s veral outputs permitting adjustment or selection of the time interval for reaching the refrigeration temperature by means of a switch 332, One of the outputs is manually selected or connected to the reset termillal o-f the flip--flop 324 so that at the expiration of the selected time interval, the flip-flop 324 -is reset, and the blocking si~nal is removed from the input of OR
gate 320. By the elld of the timed interval the evaporator Ishould have been lowered to the normal re-frigeration temperature, ¦and the temperature signal -from the thermosta$ 240 should have -Ireturned to its l-state to continue to hold the transistor 326 in its nonconductive state and block the alarm. At any subsequent ¦time when the temperat~lre of the evaporator rises, the blocking jsignal is removed and the transistor 326 conducts and actuates ¦the alarm indicator 234 and common alarm 246.
~15 ¦ Fig. 7 illustrates a d.c. power supply means that is prefera~ly utilized for energizing the master control 3~J the individual controls 40, 42, 44 and the digital time clock 50 from ' -60 cycle utility power. It will be understood that in the event ,o~ a power ~ailure and re-establishment of power, the digital Iclock witho~lt an internal nlemory resumes its co-lntin~ or timing ,function at an unpredictable time. Also many of the solid state components s~lch as the decoders 52, 54 lose track oi their se- ~
Iquencing. ~Yhen certain or all of the evaporators are scheduled . -¦!~or timed defrosting, it is conceivable that UpOII restoration of power the eVapOratOlS in need o-f de-frost prior to the failure ~ould Inot be reached for an inordinately long time because the solid 'state components cannot per-form a memory function.
. ~ _~o~
I . I
li !

! !
1 ~13~679 IFor this reason, a d.c. power supply 340 for the electrical system is augmented by an au~iliary battery 350.
Since only the eo-lnting circuits in the time clock and other ¦selected digital components in the master control 38 and indi~
¦dual controls 40, 42, 44 are eritical to the memory function, land because all of the components could readily drain the battery, !
: ~more than ttvo voltage terminals are provided. There is at least one terminal 342 of one polarity and two terminals 344 and 346 of Ithe opposite polarity energized by the power supply ~vhen utility ¦power is on. The auxiliary battery 350 or other emergency po~er souree is eonnected bet~veen the terminals 342 and 344 and the elock 50 and other eritical components are connected with these terminals as indicated by the re-ferenee numerals in box 348.
;` The remaining eomponents possibly including the time display of the eloek eonnect with terminals 342 and 3~6. The blocking diode 354 isolates the battery ~rom such remaining components so they are not energized during a power outage. The diocle 352 <
proteets the battery from being overeharged by the power supply and proteets the system components against inadvertent polarity reversal when the battery is installed. The diode 356 serves a resistive function and matches the diode 354 so that the po~ver supply voltage applied to the components conneeted ~ith terminal 346 is the same as the voltage applied to components conneeted with terminal 344. Thus the battery 350 and the connected eomponents provide a memory for the various timing lunc-¦tions a ensure thRt upon the restoration oF utility _~_ I
I ,~

i~ 2~

I" . ~
, power, the defrosting sequence ~vill resume ~rom the point at which po~ver was lost.
l In sum~ary, the re~rigeration system illustrated in ¦¦ Fig~ 1 has independently de~rosted evaporators whose operation i lS regulated by a master control 3S and a plurality of individual controls ~0, ~2J 44 respectively. In a timed mode of operation, ¦ time signals arederived from a digital time clock and in a demand mode the indi~idual contxols xespond to command signals from ~rost sensors. Testing of the individual controls is per-~10 ¦ ~ormed by driving the time clock at an accelerated rate to the programmed defrosting time. After every testing, time-set$ing-and defrostin~ opexation, the individu~ controls and their I associated evaporators may be scanned in order o~ priority to j detect which evapora-tor is the next ullit in need o~ de~rost.
I The entire control system can be embodied in solid state form for ~¦ high reliability and compact installation.
I While the present invention has been described in a ¦
pre~erred embodiment, it will be understood that numerous modi~
~ cations and substitutions can be made without departing ~rom the i spirit of the invention. Most clearly, although the digital clock decoding technique provides a convenient device ~or ob- -~ taining widely spaced time signals ~or various de~rostin~ opera-I tions, the timing signals can also be obtained from digital or ~ analog timing devices in othex ways. The priority scanning l, techn que enables a clcar system of priorities to beestablished ,1, ' I

for the evaporators in various refrigeration cabinets, but no scanning is necessary and other scanning devices such as shown and described in U. S. Patent 4,151,722 referenced above can be used instead. The fast clocking feature for testing is integrated in the control system in a convenient manner when the testing device is a digital clock but it can also be utilized with other timing devices. Naturally, the scanning and testing functions may exist together or separately in a refrigeration system. While the individual defrost control and the master control have been illustrated in a solid state form, it should be understood that the general functions of the controls can be accomplished with other digital or analog equipment. Accordingly, the present invention has been described in several forms by way of illustration rather than limitation.

Claims (32)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A control apparatus for a refrigera-tion system having a plurality of evaporators and defrosting equipment connected to defrost each of the evaporators in-dependently of the others comprising:
timing signal generating means having an adjus-table speed for producing at an adjustable rate timing signals from which the defrosting of individual evaporators are scheduled;
controlled switching means connected between the timing signal generating means and the defrosting equipment for actuating in response to the timing signals individual portions of the equipment associated with the respective evaporators and thereby switching the corresponding evapora-tors into a defrosting mode when a timing signal for said evaporator is produced; and testing means connected in controlled relationship with the timing signal generating means for increasing the rate at which the timing signals are generated and for there-by switching the evaporators into their defrost modes at accelerated points of time.

2. A defrost control apparatus for a plurality of evaporators as defined in Claim 1, further including indicating means associated with each of the evaporators for identifying the evaporators in the defrost mode indivi-dually.

3. A defrost control apparatus for a plurality of evaporators as defined in Claim 1, wherein:
the testing means includes test inhibiting means for preventing the generation of timing signals at an in-creased rate under selected conditions.

4. A defrost control apparatus as defined in Claim 3, wherein:
the controlled switching means provides a defrost signal whenever a portion of the defrosting equipment is actuated to defrost one of the evaporators; and the test inhibiting means is responsive to the defrost signal from the controlled switching means to pre-vent the generation of timing signals at an increased rate whenever one of the evaporators under test is in the de-frost mode.

5. A defrost control apparatus for a plurality of evaporators as defined in Claim 1, wherein:
the controlled switching means comprises a plura-lity of control switches associated respectively with the plurality of evaporators;
the testing means includes a plurality of test initiating means associated respectively with the plurality of control switches for selectively operating the switches and testing the individual evaporators;
a plurality of lockout means are interposed between the timing signal generating means and the plura-lity of control switches respectively for interrupting timing signals, and each of the lockout means is responsive to the test initiating means of the evaporators other than the initiating means for its own evaporator whereby the evaporators other than the one under test are prevented from responding to the timing signals during a test.

6. A defrost control apparatus for a plurality of evaporators as defined in Claim 1, wherein:
the controlled switching means for a plurality of evaporators comprises a corresponding plurality of con-trol switches associated respectively in controlling relationship with portions of the defrost equipment and the plurality of evaporators, and producing a defrost signal when an associated portion of the defrost equipment is ac-tuated; and a plurality of defrost lockout means are inter-posed between the timing signal generating means and the plurality of control switches respectively or preventing the transmission of timing signal to the respective control switches in response to a defrost signal from one of the other control switches.

7. A defrost control apparatus for a refrigera-tion system as defined in Claim 1, wherein the controlled switching means comprises a plurality of solid state swit-ches connected with the individual portions of the defros-ting equipment and the associated evaporators respectively, each of the switches being actuated by a clock pulse.

8. A defrost control apparatus for a refrigera-tion system as defined in Claim 7, wherein the solid state switches are "D"-type flip-flops.

9. A defrost control apparatus for a refrigera-tion system as defined in Claim 1, wherein the timing signal generating means comprises a time clock having a digital display.

10. A defrost control apparatus for a refrigera-tion system as defined in Claim 9, wherein:
the digital display is comprised of numeral ele-ments excited in sequential and predetermined patterns to manifest a changing time display; and decoding means are included in the timing signal generating means for reading the predetermined patterns and producing a timing signal on the occurrence of a selected pattern.

11. A defrost control apparatus for a refrigera-tion system as defined in Claim 1, wherein the timing signal generating means comprises:
a time clock having a digital time display formed by numeral elements receiving periodic electrical excita-tions; and decoding means connected with the time clock and responsive to a selected excitation condition of the numeral elements for producing a timing signal at a pre-determined time.

12. A defrost control apparatus for a refrigera-tion system as defined in Claim 11, wherein the time clock is an electronic clock having illuminated display numerals.

13. A defrost control apparatus for a refrigera-tion system as defined in Clalm 11, wherein:
the time clock has a digital time display in which the numeral element for one digit comprises a plurality of light-emitting segments.

14. A defrost control apparatus for a refrigera-tion system as defined in Claim 13, wherein the light-emitting segments are comprised by a plurality of light-emitting diodes.

15. A defrost control apparatus for a refrigera-tion system as defined in Claim 13, wherein the light-emitting segments comprise seven segments arranged to form decimal integers.

16. A defrost control apparatus for a refrigera-tion system as defined in Claim 11, wherein:
the numeral elementsof the digital time display are comprised of a plurality of display members excited electrically in a cyclic order and in pre-established pat-terns to form a changing time display; and the decoding means is connected to selected ones of the display members and is responsive to the electrical excitation condition of the selected members in certain of the pre-established patterns to produce the timing signal.

17. A defrost control apparatus for a refrigera-tion system as defined in Claim 16, wherein the decoding means is responsive to the electrical excitation condition of selected members in several of the pre-established pat-terns to produce timing signals at several different times.

18. A defrost control apparatus for a refrigera-tion system as defined in Claim 16, wherein the decoding means is responsive to the electrical excitation condition of selected members in a certain of the predetermined pat-terns which condition is repeated at periodic intervals, whereby a series of timing signals is produced, and the decoding means further includes sequencing means driven by the series of timing signals and having a plurality of out-puts excited in sequence as the driving signals are received whereby the outputs of the sequencing means produce further timing signals at spaced intervals of time.

19. A defrost control apparatus for a refrigera-tion system as defined in Claim 11, wherein:
the digital time display includes numeral elements having seven individual segments excited in various combina-tions and patterns to form decimal integers; and the decoding means is connected to selected seg-ments and responsive to the excitation condition of the selected segments to produce the timing signals.

20. A method of testing the defrost controls in a refrigeration system in which a plurality of evaporators are scheduled to be defrosted at different times in res-ponse to defrost signals generated by a time clock compri-sing:
driving the time clock at an accelerated rate at least until the clock reaches a time when a given evapora-tor is scheduled for defrosting and a defrost signal for the given evaporator is generated; and determining if the defrost signal for the given evaporator is generated at the scheduled time.

21 A method of testing the defrost controls as defined in Claim 20, wherein the time clock is a digital clock.

22. A method of testing the defrost controls as defined in Claim 20, wherein the defrost controls include indicator means for indicating defrosting of the given evaporator; and the step of determining comprises examining the indicator means for a defrosting indication.

23. A method of testing the defrost controls as defined in Claim 20, wherein:
the step of driving the time clock comprises dri-ving the time clock at an accelerated rate until the time for defrosting a selected evaporator is reached, and an additional step comprises inhibiting the defrost controls from responding to all defrost signals other than the signal generated for the selected evaporator.

24. A method of testing the defrost controls in a refrigeration system as defined in Claim 20, wherein the time clock has a time display and an additional step in the method includes checking the time display for correspondence with the scheduled time for defrosting when the defrost signal for the given evaporator is generated.

25. A method of testing the defrost controls as defined in Claim 24, wherein the time clock is a clock having a digital display and an additional step in the method includes stopping the time clock when the defrost signal for the given evaporator is generated in order to check the display.

26. A method of testing the defrost controls as defined in Claim 20, further including the step of reset-ting the time clock after the step of determining.

27. A method of testing as defined in Claim 20, wherein the time clock has a digital display formed by nume-ral elements having energization conditions corresponding to given display times, and wherein the generation of the defrost signals comprises:
determining the energization condition of the numeral elements corresponding to a preselected time;
monitoring the energization condition of the numeral elements while the time clock is operating, to de-tect the energization condition corresponding to the pre-selected time; and generating a time signal when the energization condition corresponding to the preselected time is detected.

28. A method of testing as described in Claim 27, wherein the step of determining a corresponding energization condition includes determining both energized and non-energized conditions of the numeral elements.

29. A method of testing as described in Claim 27, wherein the numeral elements of the time clock are comprised by multiple segments energized in various combinations and patterns to produce images of different numerals and the step of determining the energization condition of the numeral elements comprises determining the energization condition of the segments.

30. A method of testing as described in Claim 29, wherein one of the numeral elements consists of seven segments.

31. A method of testing as defined in Claim 27, wherein the step of determining comprises determining a particular energization condition of the numeral elements repeated at given time intervals, and the step of generating comprises generating a time signal on each occurrence of the particular energization.

32. A method of testing as defined in Claim 31, further including the steps of counting the timing signals generated with each occurrence of the particular energiza-tion and producing an accumulated time signal upon the attainment of a particular count.