Abstract:
A refrigerant monitor and alarm includes a sensor positioned to detect the level of liquid state refrigerant in the system and provide an electrical output signal therefrom, a digital display for displaying the refrigerant level, and a circuit coupling the digital display to the sensor for actuating the digital display. In a preferred embodiment, the level display is a bar-graph LED-type display incorporated on a control panel also including a refrigerant level alarm and other parameter alarms.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a monitor and alarm system for a central refrigeration installation for refrigerated display cases. 
     In commercial refrigeration installations for supermarkets where a number of refrigerated display cases are employed, typically a plurality of refrigerant compressors are utilized to supply high pressure liquid refrigerant to the evaporators contained in the display cases. Typically, a bank of such compressors will be coupled in parallel between a common input refrigerant manifold and an output manifold which, in turn, is coupled to a receiver containing a mechanical refrigerant liquid level sensor. The evaporators of each refrigerated display case are then commonly coupled to the refrigerant receiver and the outputs of the evaporators return to input manifold completing the refrigerant flow path. 
     In the past, a mechanical dial-type refrigerant level float was mounted to the receiver to provide a local visual indication of the liquid level. Also, a separate fixed alarm switch, set for approximately 20% of liquid level, was provided to provide an alarm output signal at the fixed level for activating a suitable alarm to the system operator. Systems also typically include oil failure sensing switches at each compressor for detecting the oil level contained in each compressor and a remote panel indicating oil level failures as well as monitoring other functions such as suction and discharge pressures at the input and output manifolds, respectively, and a voltage sensor to detect the loss of any one of the three phase input power employed for powering the compressors. 
     Thus, although some form of monitoring was provided for some conditions in such a system, the known prior art does not provide an integrated monitoring and alarm system whereby a central panel is provided to display all of the monitored fault functions as well as provide, in addition to the alarm indications, a display of the actual refrigerant level. 
     SUMMARY OF THE PRESENT INVENTION 
     Systems embodying the present invention include a sensor positioned to detect the level of liquid state refrigerant in the system and provide an electrical output signal therefrom, a digital display for displaying the refrigerant level, and circuit means coupling the digital display to the sensor for actuating the digital display. In a preferred embodiment, the level display is a bar-graph LED-type display incorporated on a control panel also including a refrigerant level alarm and other parameter alarms. 
     Such a system thereby provides a continuous display to maintenence personnel of the refrigerant liquid level so preventive maintenance can be achieved before an alarm condition exists as well as the other alarm indications all at a convenient, centrally located display panel. 
    
    
     These and other features, objects and advantages of the present invention will become apparent upon reading the following description thereof together with reference to the accompanying drawings in which: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front elevational view of a display panel embodying the system of the present invention; and 
     FIG. 2 is a block and schematic electrical circuit diagram of the system embodying the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring initially to FIG. 1, there is shown a display panel 10 for the alarm and monitoring system of the present invention. Panel 10 can be located centrally at an installation and remote from the compressors so that it is easily monitored by supervisory or maintenance personnel. The panel 10 includes a horizontal row 20 of six LEDs (light emitting diodes) 11-16, each uniquely associated with one of up to six different compressors. As will be described below, these LEDs indicate for each of up to six compressors in an installation oil levels which fall below a predetermined safe level. Below the row 20 of oil failure indicating LEDs is a high refrigerant discharge pressure LED 17 which is activated when the discharge pressure at the output manifold is excessively high indicating an obstruction in the output refrigerant circuit, air in the refrigerant circuit or condensor fan failure. Below the high discharge LED 17 is a high suction LED indicator 18 which is activated by the electrical circuit, shown in FIG. 2, when the input pressure reaches, for example, 45 psi gauge indicating, for example, a valve problem in the compressor. Below the high suction LED 18 there is a phase loss LED 19 which is coupled to a commercially available phase loss detector for the three phase, 220-volt AC power supplied to the compressors. If any of the three phases are absent due to a power failure, the detector will provide an output signal employed for activating phase loss LED 19. 
     The remainder of the alarm and monitor system provides a refrigerant alarm level indication as well as a continuously activated refrigerant liquid level display. The refrigerant alarm level indication is provided by an LED 22 while the percentage of liquid level is displayed on a display panel 23 including ten vertically aligned and spaced LEDs 24-33 adjacent of which is provided indicia 34 identifying the percentage liquid level present. Indicia 34 is divided, in the preferred embodiment illustrated, in increments of ten percentage points, and as will be described below, the display 23 can be operated as a continuous bar-graph or dot display which is selectable by rear panel control as is the refrigerant alarm level and time delays for the display of selected alarms such as refrigerant level and suction pressure. 
     Finally, the front of the display panel 10 includes an alarm reset switch 35 which can be depressed once an alarm condition is noted and it is desired to deactivate an alarm 60 (FIG. 2) which may be an audible alarm which can be positioned integrally behind the panel or at a remote location. Having described the display functions provided by the monitor and alarm system, a description of the electrical circuit for the display panel 10 is now described in connection with FIG. 2. 
     Initially, it is noted that circuit 40, shown in FIG. 2, incorporates the LEDs shown on the front panel and which carry the same reference numerals. The oil failure LEDs 11-16 are driven by a low voltage supply +V comprising a 12-volt supply, in the preferred embodiment, through switch contacts 41-46, respectively, of commercially available differential pressure-type-switches. Each of the switch contacts 41-46, therefore, are uniquely associated with compressors 1-6, respectively, and the contacts will close to provide a +V signal at an anode of an associated LED when the oil pressure falls below a predetermined level. The signal on the cathode of one or more activated LED will, therefore, apply a logic &#34;1&#34; to one of a plurality of inputs to logic circuit 48. 
     Circuit 48 is a plurality of NAND gates each having one input grounded, and one input serving as an input to circuit 48. The output of the gates are commonly coupled and coupled to an output terminal 49 of circuit 48 such that a logic &#34;1&#34; at any one of the inputs of circuit 48 will provide a logic &#34;1&#34; output signal at output terminal 49. The output signal, constituting an alarm condition output signal, is applied to a latch circuit 50 by a three-position, single pole switch 51. Switch 51 can be placed in a manual position, as illustrated, by which the latch circuit 50 will respond to the presence of an input logic &#34;1&#34; alarm signal to go into a latched condition providing a relay driving output signal at terminal 52 which remains at a logic &#34;1&#34; condition and is applied to the alarm control relay 56 which, in turn, drives and activates alarm 60. Thus, when a signal on the wiper arm of switch 51 is a logic &#34;1&#34; level due to the existence of any alarm signal applied thereto, when in the manual position, latch 50 will provide a continuous alarm output signal for relay 56 until a reset button switch 35, coupled to the latch, is actuated. Latch 50 can include a standard set-reset flip flop. 
     When swtich 51 is in the automatic or central position, the latching function of circuit 50 is bypassed and the driving signal on switch 51 is applied directly to output terminal 52 which controls relay 56 to actuate the alarm 60 coupled to the output of relay 56 whenever an alarm signal exists. When the alarm signal is discontinued, the system automatically shuts off. When switch 51 is in the off position, the alarm 60 is not activated by the existance of an alarm condition or an associated lighted LED, however, the LED display is functional to provide a visual indication of an alarm condition on display panel 10. 
     The high suction LED 18 is similarly activated from the +V source through a pressure actuated switch 62 located in the input manifold of the system to provide a logic output signal at its cathode when a suction pressure of approximately 45 psi gauge is reached. The signal at the cathode of diode 18 is applied to an adjustable time delay circuit 64, which can be set for from 1 to 10 minutes, or other selectable time period if desired, to provide an output signal at output terminal 65 thereof. This signal is, in turn, applied to an input of circuit 48, as illustrated, to provide an alarm signal when high suction pressure is detected after the predetermined selectable delay. The time delay circuit 64 prevents false alarms and may include a clock oscillator and a selectable counter such that the signal from diode 18 will activate the oscillator and counter circuit to provide an output pulse at terminal 65 after a predetermined selectable time period has elapsed from the closure of contact 62. The suction pressure switch 62 is of conventional design and commercially available. 
     The high discharge LED 17 is similarly coupled to the source of +V through a high discharge pressure switch 66 located in the output manifold of the system and of conventional design and commercially available. Switch 66 closes to provide a signal to the anode of diode 17 when pressures of approximately 250 to 300 psi have been reached indicating a malfunction condition. The cathode of diode 17 is coupled to an input of circuit 48 to provide an alarm signal. 
     Similarly, the phase loss sensor provides a contact 68 which closes upon loss of any one of the three phases of power supply voltage for any of the compressors in the system and couples a signal through LED 19 to circuit 48 indicating an alarm condition exists. 
     Thus, any one or more of the oil failure, suction, discharge pressure or phase loss sensors will provide an alarm condition signal through latch 50 to control relay 56 and activate alarm 60. Alarm 60 can be an audible alarm such as a bell or siren or a combination of audio/visual alarms which can be integrally included on the panel 60 or located remotely at, for example, a supervisor or central control area different than the location of panel 10. Switch 51 typically will be mounted on the back of panel 10 so that the alarm cannot be inadvertently turned off. 
     The refrigerant liquid level monitoring system employs an analog liquid level transducer 70 comprising a potentiometer 71 coupled to input terminals 3 and 4 of an LM3914 integrated circuit 80 and has a wiper arm coupled to input terminal 5 of the circuit for providing an analog varying DC voltage to circuit 80 representing the level of refrigerant in the receiver. The wiper arm 72 is mechanically coupled to a float 73 to be moved by the float positioned to float within the liquid refrigerant. The sensor thus forms a variable voltage source with the electrical signal at wiper arm 72 coupled to an input terminal 82 of a digital comparator 84 having a reference input terminal 86 coupled to an adjustable reference level voltage source comprising a potentiometer 83 coupled between +V and ground with its wiper arm coupled to input terminal 86 of the comparator. The voltage selected by resistor 83 can be selected such that for any predetermined level or refrigeration, as indicated by the voltage supplied at potentiometer arm 72, will cause comparator 84 to provide a logic &#34;1&#34; output level when the refrigerant level falls below the desired level. The logic &#34;1&#34; signal is applied through the refrigerant alarm level LED 22 to a time delay circuit 88 substantially identical to circuit 64 and having a selectably adjustable alarm delay of from 1 to 10 minutes. Circuit 88 has an output terminal 89 coupled to an input of circuit 48 for providing a signal for activating the alarm 60 when switch 51 is in the manual or automatic modes. 
     Wiper arm 72 is also electrically coupled to output 9 of circuit 80 to provide either a dot or bar-graph display 23 through the LEDs 24-33 having their anodes commonly coupled to the +V supply and their cathodes coupled to the pin numbers indicated in the schematic. A single pole-double throw switch 90 is coupled between pins 9 and 11 of circuit 80 and can be moved into the position shown to provide a dot display for display panel 23. Thus, for example, for a level of 70% of refrigerant, the dot mode would light LED 30 only. If switch 90 is moved to the remaining position commonly coupled to the anodes of the LEDs a level of 70% would activate LEDs 24-30, inclusively. The analog voltage applied to input pin 5 of circuit 80 thus causes the actuation of the level representing LEDs. A calibration potentiometer 92 is coupled between pins 6 and 7, as illustrated in the Figure, and is adjusted to provide a 100% scale LED indication when the refrigerant level is at the 100% level. 
     Thus, with the system of the present invention, a display panel is provided which displays not only alarm conditions but also provides a continuous display of discrete refrigerant liquid levels. The resolution of display 23 can be increased by adding additional circuits 80, if desired, although the 10% increments have been found suitable for commercial refrigeration applications. By providing a sensor 70 which comprises, in the referred embodiment, a 10K-ohm precision potentiometer coupled to a float through a gear mechanism that the full excursion of the pot occurs between the 0 and 100% levels, an analog DC varying voltage representative of the liquid level is provided and can be used to provide a signal for the dual purposes of providing alarm input signal information to comparator 84 as well as a continuous level signal to circuit 80. If desired, a different continuous display other than the descrete LEDs, as for example, a digital numerical display such as an LCD can be provided. 
     These and other modifications to the preferred embodiment will, however, become apparent to those skilled in the art and will fall within the scope and spirit of the invention as defined by the appended claims.