IMPROVED OPTICAL DEFROST APPARATUS

Abstract: An optical frost sensing apparatus for detecting accumulation on the evaporator (16) of a refrigeration system (14) and activating a controller (30) for switching on and off a defrosting means (28) for defrosting the evaporator (16). An emitter (54) generates electromagnetic radiation along a path (62) to a detector (52) axially aligned therewith and over barrier (58) interposed therebetween but out of the way. Barrier (58) presents an edge for frost build-up and detection when the frost interferes with radiation path (62). Emitter (54), detector (56) and barrier (60) are commonly included in housing (50) along with circuit (32) for regularly pulsing emitter (54) and providing an output to defrost controller (30) when detector (56) senses radiation intensity above a predetermined amount. A lack of output from detector (56) activates controller (30) to turn on defrost means (28). Circuit (32) produces a pulse when capacitor (75) has enough charge thereon to reverse bias diac (68) to cause a current pulse through LED (54). This cuts off diac (68) to permit recharging of capacitor (74). If the intensity of light received at LASCR (56) is sufficiently large, as set by resistor (80) between the gate and cathode thereof, then a low resistance path is established through LASCR (56) for producing an output to controller (30) on conductor (33).

Description: IMPROVED OPTICAL DEFROST APPARATUS Technical Field This invention relates to an evaporating coil defrost initiation control for various types of refrigera¬ tion apparatus and more particularly to an improved optical defrost detecting and initiation apparatus that utilizes a pulse circuit to periodically pulse an emitter in the initiation apparatus for generating the electromagnetic radiation utilized in the frost detection. Background Art The representative prior art is disclosed in the following U.S. Patents: 3,961,495 (Beauvent, et al.); 3,188,828 (Wayne); and 3,120,108 (Pansing) . The patent to Beauvent, et al. discloses a frost detecting device adapted to be attached to the fins of a refrigerator evaporator coil. The device includes an infrared radiation emitting means and a radiation sensitive means mounted on a body support attachable to the evaporator coil fins. The infrared emitter directs a beam of infrared radiation to the coaxially aligned detector through a slot cut into one of the fins. As the frost bridges the slot in the fins, the infrared radiation is absorbed or scattered by the frost and a lower intensity reaches the detector. A control circuit pulses the infrared emitter at a predetermined frequency in order to eliminate other undesirεd signals. O PI The patent to Pansing discloses a light source and a detector mounted in a spaced coaxial relationship for emitting and receiving a light directed through an 0 aperture in the cooling fins of an evaporator coil. As the frost fills the aperture, the light beam is blocked and less light reaches the detector thus signalling time for defrost. The patent to Wayne discloses a light source and 5 a photocell spaced apart and optically separated by a barrier that blocks all light transmissions from the light emitter to the photocell. However, as frost or ice forms on the top edge of the barrier, light is refracted through - the frost or ice from the light source to the photocell 0 and around the barrier. As the thickness of the frost or ice increases, the quantity of light refracted to the photocell increases to a predetermined level to signal defrost. 5 Disclosure of the Invention In accordance with the present invention, an optical frost sensing apparatus for detecting frost accumulation on the evaporator of a refrigeration system is provided that includes an emitter (preferably a light 5 Q emitting diode or LED) for generating a electromagnetic radiation over a preselected narrow range of wavelengths, and a detector (preferably a light admitting silicon con¬ trolled rectifier or LASCR) that is axially aligned with the emitter for receiving the electromagnetic radiation 55 and generating an electrical signal in response thereto if the intensity of the radiation exceeds a predetermined threshold intensity. A metallic, heat-conductive barrier is inter¬ posed transversely between the emitter and detector and g 0 has one edge terminating near, but clear of, the axial path of the emitted electromagnetic radiation for permit¬ ting unhindered transmission of the radiation when the barrier is free of frost, but interposing frost formed on O PI Λ'AT10 the exposed edge of the barrier into the axial radiation path to absorb and scatter the radiation. A slotted body means mounts the emitter and detector in a spaced relationship on opposite sides of the slot, with the barrier mounted in the base of the slot. The body carries the emitter, " detector and barrier with the barrier including a contactor positioned in contact with ' the evaporator of the refrigeration system so as to place it in a heat transfer relationship thereto for causing frost to form on the barrier. An emitter pulsing circuit is included and connected to the emitter and detector for pulsing the emitter at preselected time intervals. The network comprises an RC network and a diac, the diac and capacitor of the RC network being connected in parallel with the emitter. The resistor of the RC network is connected in series with the diac. The capacitor charges with the applied ac source current until the diac reverse conducts. When this occurs, the capacitor discharges through the reverse conducting diac and causes the emitter to conduct, with the diac reverse conducting again after discharge of the capacitor for permitting the capacitor to re-charge. Brief Description of the Drawings . In order that the manner in which the above- recited features, advantages, and objects of the invention are attained can be understood in detail, a more particular description of the invention may be had by reference to a specific embodiment thereof which is illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the appended drawings illustrate only a preferred embodiment of the invention and therefore are not to be considered limiting of its scope for the invention may admit to further equally effective embodiments. OMPI « NA P T°O^ In the Drawings: . 100 Figure 1 is a schematic representation of a typical refrigeration or air condition system utilizing a preferred embodiment of an optical frost sensing apparatus in accordance with a preferred embodiment. Figure 2A is a top view of the frost sensing 105 apparatus of Figure 1 mounted on an evaporator or coil. Figure 2B is a side view of the apparatus shown in Figure 2A. Figure 2C is an end view of the apparatus shown in Figure 2A. 110 Figure 3 is an electrical schematic diagram of a preferred embodiment of the pulsing circuit connected for operation of the emitter and detector. Best Mode for Carrying Out the Invention 115 Referring now to Figure 1, the optical defrost apparatus in accordance with the present invention is • shown in a typical application. A refrigerator (or freezer) 10 is shown having an inner refrigerated space 14 that is cooled in a conventional manner by evaporator 120 (cooling) coils 16, sometimes referred to merely as "evaporator", within an evaporator compartment 12 of a conventional closed refrigeration system. The refrigeration system comprises a compressor 20 connected to evaporator 16 by means of suction line 18 for receiving 125 the refrigeration fluid in a gaseous form, compressing the fluid and distributing it through line 22 to condensor coils 24 where the refrigeration fluid is condensed to a liquid. The liquid refrigeration fluid is then applied through an expansion valve 26 to evaporator 16 in 130 compartment 12 for cooling the refrigerated space 14. Evaporator 16 has a plurality of heat exchange fins 17 mounted thereon (only a portion of the coil structure is shown with fins for simplicity). An evaporator defrost means 28, typically an 135 electrical defrost heater, is provided to defrost / ^3K Acr evaporator 16 and' ins 17 when the accumulation of ice or frost needs to be removed from the evaporator surface to increase the heat exchange efficiency of the evaporator. AC electrical power for the system is provided from a conventional source by conductors 38 and 42. Lines 38 and 40 are connected to compressor 20, with line 38. being connected directly to defrost means 28. Line 42 is connected to a defrost control 30 which controls defrost in response to the action of optical frost sensing device 32. Defrost control 30 controls the operation of defrost means 28 through conductor 36, and could also control the operation of the compressor 20 through conductors 48 and 44 and a low temperature thermostat switch 46. Optical frost sensing device 32 provides signals to defrost control circuit 30 through conductor 33 and is connected to the source voltage through conductors 34 and 38. While the above description of the refrigerating system 10 has been explained in terms of a refrigerator or freezer, the refrigerating system 10 could be any refrigerating means such as an air conditioning system or the refrigerating phase of a heat pump system. Further, evaporator defrost means 28, while described in terms of a conventional electrical heater coil, can be any suitable means for defrosting an evaporator surface, including - reversing refrigerant flow through the evaporator to enable the hot refrigerant to warm and defrost the evaporator. Figures 2A, 2B and 2C show the preferred embodi¬ ment of an optical frost sensing device 32 in accordance with the present invention, mounted on evaporator 16. Device 32 comprises a generally rectangular body or housing 50 having a transverse slot 52 therein. Housing 50 is conventionally made of an epoxy material and carries within it the electronic circuit to be described hereinafter as shown in Figure 3. Also, housing 50 provides establishing a fixed relationship to each other of an LED emitting device 54, an electromagnetic radiation detection device 56, such as preferably an LASCR, and metallic barrier 58. The barrier is described more fully 175 below insofar as it relates to emitter 54 and detector 56j however, barrier 58 also includes a contactor extension 60 which is positioned against evaporator 16 in metal-to-metal contact. The contactor is preferably held in this position so that it does not move away from 180 contact inadvertently. The top edge of barrier 58 is mounted in the bottom or base of slot 52 so as to be adjacent, yet well apart (preferably below) from the axial path of the electromagnetic radiation traversing slot 52 between 135 emitter 54 and detector 56. As illustrated, electro¬ magnetic radiation path 62 is unhindered by barrier 52 when the coil, and hence, barrier 58 by virtue of contactor 60, is free of frost. However, as frost forms over the surface of 190 evaporator 16, it also forms over the surface of the bar¬ rier between emitter 54 and detector 56. The accumulated frost grows eventually until a portion of the electro¬ magnetic radiation along path 62 is interfered with, such as by reflection, scattering and/or absorption, to leave a 195 diminished quantity of radiation reaching detector 56. If the frost grows thick enough, substantially all of the electromagnetic radiation from emitter 54 will be diverted, leaving little or no radiation to reach detector 56 along path 62 for purposes to be hereafter more fully 200 explained. In Figures 2A and 2C, it may be seen that power and signals as explained below enter housing 50 via conductors 33 and 34. The body or housing 50 may be molded or potted around an embedded portion of emitter 54, 205 detector 56 and barrier 58 and the electronic circuit shown schematically in Figure 3 to form an integral device. The material of which housing 50 is constructed is preferably an epoxy resin or similar material to provide structural stability, shock resistance, good 2io thermal insulation qualities and a permanent moisture sealing means. The barrier-and-slot arrangement is such that when defrosting occurs and the frost turns to water, the water does not appreciably bubble on the edge of the 2i5 barrier. That is, the width of the edge is sufficiently small and the depth of the slot is sufficiently deep that the nonfrosted barrier presents no hindrance to path 62. Further, the slot provides a convenient runoff guide for the melted frost. 220 A preferred embodiment of solid-state circuitr for the frost optical sensing and initiation means 32 is disclosed in Figure 3. Emitter 54 and detector 56 are mounted in body 50 with the remaining circuitry, as shown in Figures 2A, 2B and 2C. Conductor 33 from the defrost 225 control circuit 30 (see Figure 1) is connected as an input line to diode 64. Diode 64 is then successively connected to resistor 66, a diac 68, an LED (emitter) 54 and resistor 72 to ground potential through interconnecting conductors 65, 67, 69 70, 73, -34 and 38, respectively. A 230 capacitor 75 is connected in parallel with diac 68, LED 54 and resistor 72 through conductors 74 and 76, inter¬ connecting to conductors 67 and 73, respectively. An LASCR 56, acting as a detector and switch means, is connected in parallel with resistor 66 and capacitor 75 by 235 conductors 78 and 79, interconnecting to conductors 65 and 34, respectively. The gate or trigger input of LASCR (detector) 56 is connected to a resistor 80 through conductors 81 and 82 connected to conductor 79. Resistor 80 determines the trigger or threshold voltage for turning 240 on or off LASCR 56. Industrial Applicability In operation, the AC voltage is applied through the defrost control circuit and conductor 33 to the anode 245 of diode 64. The series paths through diode 64, resistor 66, and capacitor 75 or through diode 64, resistor 66, diac 68, LED 54 and resistor 72 are high resistance paths and only a small current (on the order of microamps) is passed. Initially, the capacitor 75 slowly charges until 250 it reaches a selected voltage level that causes reverse conduction of diac 68 (conveniently about 32 volts) which causes capacitor 75 to discharge and the (emitter) LED 54 to conduct, thus generating electromagnetic radiation that is directed toward the (detector) LASCR 56. However, as- 255 soon as capacitor 75 discharges, the diac 68 reverses, shutting off LED 54 and permitting capacitor 75 to begin charging again. Accordingly, it can be seen that LED 54 will be "turned on" at regular intervals determined by the RC time constant of resistor 66 and capacitor 75 acting as 260 a pulse circuit means, and the LED will generate succes¬ sive pulses or bursts of electromagnetic radiation directed toward LASCR 56. If there is no ice or frost on evaporator 16, for example, as shown in Figure 2A, or if the ice or frost 265 thickness is insufficient to scatter or absorb most of the pulses of electromagnetic radiation generated by LED 54, then the electromagnetic radiation received by LASCR 56 will generate a voltage which, if it exceeds the threshold voltage determined by resistor 80, causes the LASCR to 270 conduct. The series path through diode 64 and LASCR 56 is a- low resistance path which the LASCR is conducting and, therefore, a large current will flow through conductor 33 for signalling defrost control 30 to maintain defrost means 28 in an unenergized condition. However, during the 275 interval when no electromagnetic radiation is received from LED 54, LASCR 56 stops and capacitor 75 charges again to pulse LED 54 through diac 68. However, when insufficient electromagnetic radiation reaches LASCR 56 to cause conduction, for 280 example, when frost blocks radiation path 62 as shown in Figure 2B, the lack of a large current flow through diode 64, LASCR 56 and conductor 33 signals defrost control 30 that defrost means 28 needs to be energized. The optical frost sensing device 32 circuit shown in Figure 3 285 discloses a simple, solid state optical frost sensing means for cooperating with a defrost control 30 to control defrost action. Defrost control 30 may be any control that will receive the periodic singals when LASCR 56 conducts and 290 maintain the defrost means 28 when LASCR 58 signals fail to maintain a periodic rate. Such a defrost control is marketed by Altech Controls Corporation and is disclosed in copending International Application No. PCT/US81/00881, which disclosure is incorporated herein by reference for 295 all purposes. Numerous variations and modifications may be made in the structures herein described without departing from the present invention. Accordingly, it should be clearly understood that the forms of the invention herein 300 described and shown in the figures of the accompanying drawing are illustrative only and are not intended to limit the scope of the invention.

Claims: CLAIMS : 1. Optical frost sensing apparatus for detecting frost accumulation on the evaporator of a refrigeration system, wherein said system includes a demand defrost controller for switching on and off a means for defrosting the evaporator of the refrigeration system, comprising an emitter for generating electromagnetic radiation in a preselected wavelength range, a detector axially aligned with and spaced from said emitter for receiving said electromagnetic radiation, a metallic barrier interposed transversely between said emitter and detector and having one edge terminating adjacent the axial path of said emitted electromagnetic radiation for permitting unhindered transmission of said radiation when said barrier is free of frost, but interposing frost formed on said one edge of the barrier into said axial radiation path to absorb and scatter radiation, body means mounting said emitter, detector and barrier in said spaced relationship, said metallic barrier including a contactor positioned for contacting the evaporator of the refrigeration system, and a pulsing circuit connected to said emitter and O PI said detector for -pulsing on said emitter at regular intervals and generating an electrical signal output to the controller for preventing the defrosting means from defrosting the evaporator when the intensity of said electromagnetic radiation received by said detector exceeds a predetermined threshold level. 2. The apparatus in accordance with claim 1, wherein said emitter is a light emitting diode. 3. The apparatus in accordance with claim 1, wherein said detector is a light admitting silicon controlled rectifier (LASCR) . 4. The apparatus in accordance with claim 1, wherein said metallic barrier edge is substantially straight. 5. The apparatus in accordance with claim 4, wherein the thickness of said edge is sufficiently thin and the position of said edge is sufficiently below the axial path that residual water thereon resulting from melted frost * does not hinder transmission of said radiation. 6. The apparatus in accordance with claim 1, wherein said body means includes a slotted housing mounting said emitter and detector in a spaced axial relationship on opposite sides of the slot, said edge of the barrier being mounted in the base of said slot. 7. The apparatus in accordance with claim 1, wherein said body means mounts said emitter, detector and barrier in fixed space relationship. 8. The apparatus in accordance- with claim 7, wherein said housing is constructed of an integrally molded epoxy material. 9. The apparatus in accordance with claim 1, wherein said pulsing circuit for pulsing said emitter at preselected time intervals includes a diac in. series with said emitter, and an RC network connected to said diac for receiving input current from an ac supply source that builds a charge for reverse biasing said diac, thereby discharging the capacitor of said RC network through said diac and creating pulse current through said emitter, thereby causing said emitter to conduct and removing the reverse bias from said diac to render said emitter non-conductive and allowing a subsequent charge to build up. 10. The apparatus in accordance with claim 9, wherein said detector is a gated semiconductor device, and said pulsing circuit includes a resistor connected to said gated detector for establishing a predetermined threshold level therefor. 11. The apparatus in accordance wich claim 10, wherein said detector is a light admitting silicon controlled rectifier (LASCR) , said threshold resistor being connected between the gate and the anode of said LASCR. 12. A subcombination of an optical frost sensing apparatus, comprising an emitter for generating electromagnetic radiation in a preselected wavelength range, a detector axially aligned with and spaced from said emitter for receiving " said electromagnetic radiation, a metallic barrier interposed transversely between said emitter and detector and having one edge terminating adjacent the axial path of said emitted electromagnetic radiation for permitting unhindered transmission of said radiation when said barrier is free of frost, but interposing frost formed on said one edge of the barrier into said axial radiation path to absorb and scatter radiation, body means mounting said emitter, detector and barrier in said spaced relationship, said metallic barrier including a contractor for positioning against a frost-buildup element ' to be sensed. 13. The apparatus in accordance with claim 12, wherein said emitter is a light emitting diode. 14. The apparatus in accordance with claim 12, wherein said detector is a light admitting silicon controlled rectifier (LASCR) . 15. The apparatus in accordance with claim 12, wherein said metallic barrier edge is substantially straight. 16. The apparatus in accordance -with claim 15, wherein the thickness of said edge is sufficiently thin and the position of said edge is sufficiently below the axial path that residual water thereon resulting from melted frost does not hinder transmission of said radiation. 17. The apparatus in accordance with claim 12, wherein said body means includes a slotted housing mounting said emitter and detector in a spaced axial relationship on opposite side of the slot, said edge of the barrier being mounted in the base of said slot. 18. The apparatus in accordance with claim 12, wherein said body means mounts said emitter, detector and barrier in fixed spaced relationship. 19. The apparatus in accordance with claim 18, wherein said housing is constructed of an integrally molded epoxy material.

Inventors: ALSENZ RICHARD H, ALSENZ, RICHARD, H.
Applicants: ALSENZ RICHARD H, ALSENZ, RICHARD, H.
Application year: 1982
Main classification: F25D21
IPC codes: F25D21