Abstract:
A cooling system includes a compressor rack, a controller, a gateway, and a system master. The compressor rack includes a plurality of compressors. A controller is dedicated to each compressor and includes a memory storing configuration data for the compressor. A gateway is in communication with each controller and allows the system master to command the controller to send the configuration data to the system master, whereby the system master stores a copy of the configuration data for each compressor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation of U.S. patent application Ser. No. 09/977,552 filed on Oct. 15, 2001, which is a division of U.S. patent application Ser. No. 09/515,802 filed on Feb. 29, 2000 (now U.S. Pat. No. 6,302,654). The disclosures of the above applications are incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to the control and protection of compressors. More particularly, the present invention relates to a compressor control and protection system which combines compressor temperature control, phase protection, vibration protection, oil level control and protection, pressure sensing and pulse width modulation control.  
         BACKGROUND AND SUMMARY OF THE INVENTION  
         [0003]    Scroll type machines are becoming more and more popular for use as compressors in both refrigeration as well as air conditioning applications due primarily to their capability of extremely efficient operation. Generally, these machines incorporate a pair of intermeshed spiral wraps, one of which is caused to orbit relative to the other so as to define one or more moving chambers which progressively decrease in size as the travel from an outer suction port toward a center discharge port. The means for causing the orbiting of one of the scroll members is in many cases an electrical motor. The electric motor operates to drive the one scroll member via a suitable drive shaft affixed to the motor rotor. In a hermetic compressor, the bottom of the hermetic shell normally contains an oil sump for lubricating and cooling purposes.  
           [0004]    Scroll compressors depend upon a number of seals to be created to define the moving or successive chambers. One type of seal which must be created are the seals between opposed flank surfaces of the wraps. These flank seals are created adjacent to the outer suction port and travel radially inward along the flank surface due to the orbiting movement of one scroll with respect to the other scroll. Additionally sealing is required between the end plate of one scroll member and the tip of the wrap of the other scroll member. Because scroll compressors depend upon the seals between flank surfaces of the wraps and the seals between the end plates and opposing wrap tips, suction and discharge valves are generally not required.  
           [0005]    While the prior art scroll machines are designed to run trouble free for the life of the scroll machine, it is still necessary to monitor the operation of the compressor and discontinue its operation when specific criteria have been exceeded. Typical operational characteristics which are monitored include the discharge temperature of the compressed refrigerant, the temperature of the motor windings, three-phase reverse rotational protection, three-phase missing phase/single phase protection and an anti-short cycle. The monitoring of these characteristics and the methods and devices for monitoring these characteristics have been the subject of numerous patents.  
           [0006]    Recently, it has been found that by monitoring the vibrational characteristics of the scroll machine, it is possible to predict problems with a scroll machine before these problems result in a failure to the entire system. For instance, in a refrigeration or air conditioning system which incorporates numerous scroll machines, the abnormal vibration of one of the scroll machines can result in a fracture of the refrigeration tube associated with that individual scroll machine. The fracture of this tube will result in a total loss of the system refrigerant, possible damage to property, expensive repairs and in some cases could be hazardous. Assignee&#39;s U.S. Pat. No. 5,975,854, the disclosure of which is incorporated herein by reference, disclosed a device which is capable of independently monitoring the vibrational characteristics of an individual scroll machine.  
           [0007]    Accordingly, what is needed is a system which is capable of communicating with and monitoring the operational characteristics of a compressor and/or a group of compressors. The system should have the ability to monitor all aspects of the operational characteristics of each of the compressor as well as having the ability to communicate with a central monitoring system to identify current or possible problems associated with the individual compressor. The central monitoring system can be a centralized rack gateway which communicates with each individual compressor, a rack/system control that acts as a gateway to communicate with each individual compressor or an Internet web server that communicates with a gateway associated with each compressor.  
           [0008]    The present invention provides the art with an advanced compressor control and protection system. The advanced compressor control and protection system incorporates internally integrated sensing, protection and control functions not provided by the prior art motor protection modules in use today. The control and protection system of the present invention integrates these functions with the compressor for improved overall system cost, reliability and value and thus provides improved compressor protection, simpler system wiring, diagnostics and communications. The advanced compressor control and protection system of the present invention provides a common hardware platform for a broad range of compressor modules. The system of the present invention provides a reduction in cost due to common electronics platform for all sensing and control functions, higher reliability due to improved protection because of common logic incorporating a multiplicity of sensor and status information as well as reduction in cost and improved reliability due to reduction in field wiring of individual stand-alone protection systems.  
           [0009]    The present invention utilizes a low-cost communications enabling approach using intermediate communications protocol to facilitate use of adapters and gateways for virtually any communications network with minimal cost burden on non-network applications. Multiple sensors are adapted for use internally within the compressor which provide signals which are analogous to the actual physical quantities being measured. Examples are discharge temperature, motor winding temperatures, gas pressure (suction, discharge) and differential pressures, liquid level, liquid refrigerant, relative percentage of liquid refrigerant versus oil and others.  
           [0010]    Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0012]    [0012]FIG. 1 is a vertical cross-sectional view through the center of a scroll type refrigeration compressor incorporating the control and protection system in accordance with the present invention;  
         [0013]    [0013]FIG. 2 is a top plan view of the compressor shown in FIG. 1;  
         [0014]    [0014]FIG. 3 is a perspective view of the electrical enclosure shown in FIG. 2;  
         [0015]    [0015]FIG. 4 is a side view of the compressor protection and control subsystem shown in FIG. 3;  
         [0016]    [0016]FIG. 5 is a functional block diagram of the compressor protection and control subsystem shown in FIG. 3;  
         [0017]    [0017]FIG. 6 is a top plan view of the preferred implementation of the vibration sensor which can be incorporated into the compressor protection and control subsystem shown in FIG. 4;  
         [0018]    [0018]FIG. 7 is a side cross sectional view of the vibration sensor shown in FIG. 5;  
         [0019]    [0019]FIG. 8 is a vertical cross-sectional view of a compressor having a capacity control system;  
         [0020]    [0020]FIG. 9 is a vertical cross-sectional view of a compressor having a liquid injection system;  
         [0021]    [0021]FIG. 10 is a plan cross-sectional view of a compressor having an oil injection system;  
         [0022]    [0022]FIG. 11 is a schematic illustration of the gateway options available for the compressor;  
         [0023]    [0023]FIG. 12 is a schematic representation of a control system for a plurality of compressors using various gateways;  
         [0024]    [0024]FIG. 13 is a schematic representation of another control system for a plurality of compressors using various gateways;  
         [0025]    [0025]FIG. 14 is a schematic representation of another control system for a plurality of compressors using various gateways;  
         [0026]    [0026]FIG. 15 is an oil sensor used with the compressor;  
         [0027]    [0027]FIG. 16 is another oil sensor used with the compressor; and  
         [0028]    [0028]FIG. 17 is a functional block diagram of the compressor protection and control subsystem for a semi-hermetic compressor.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0030]    Referring now to the drawings in which like reference numerals designate like or corresponding parts throughout the several views, there is shown in FIGS. 1 and 2 a scroll compressor which incorporates the compressor protection and control subsystem in accordance with the present invention which is designated generally by reference numeral  10 . While the compressor protection and control subsystem is being illustrated for exemplary purposes in association with a hermetic scroll compressor, it is within the scope of the present invention to use the compressor protection and control subsystem with other rotary compressors also. Compressor  10  comprises a generally cylindrical hermetic shell  12  having welded at the upper end thereof a cap  14  and at the lower end thereof a base  16  having a plurality of mounting feet (not shown) integrally formed therewith. Cap  14  is provided with a refrigerant discharge fitting  18  which may have the usual discharge valve therein (not shown). Other major elements affixed to the shell include a transversely extending partition  22  which is welded about its periphery at the same point that cap  14  is welded to shell  12 , a main bearing housing  24  which is suitably secured to shell  12 , a lower bearing housing  26  also having a plurality of radially outwardly extending legs each of which is also suitably secured to shell  12  and an electrical enclosure  28  (FIG. 2). A motor stator  30  which is generally square in cross-section but with the corners rounded off is press fitted into shell  12 . The flats between the rounded corners on the stator provide passageways between the stator and shell, which facilitate the return flow of lubricant from the top of the shell to the bottom.  
         [0031]    A drive shaft or crankshaft  32  having an eccentric crank pin  34  at the upper end thereof is rotatably journaled in a bearing  36  in main bearing housing  24  and a second bearing  38  in lower bearing housing  26 . Crankshaft  32  has at the lower end a relatively large diameter concentric bore  40  which communicates with a radially outwardly inclined smaller diameter bore  42  extending upwardly therefrom to the top of crankshaft  32 . Disposed within bore  40  is a stirrer  44 . The lower portion of the interior shell  12  defines an oil sump  46  which is filled with lubricating oil to a level slightly above the lower end of a rotor  48 , and bore  40  acts as a pump to pump lubricating fluid up the crankshaft  32  and into passageway  42  and ultimately to all of the various portions of the compressor which require lubrication.  
         [0032]    Crankshaft  32  is rotatively driven by an electric motor including stator  30 , windings  50  passing therethrough and rotor  48  press fitted on the crankshaft  32  and having upper and lower counterweights  52  and  54 , respectively.  
         [0033]    The upper surface of main bearing housing  24  is provided with a flat thrust bearing surface  56  on which is disposed an orbiting scroll member  58  having the usual spiral vane or wrap  60  on the upper surface thereof. Projecting downwardly from the lower surface of orbiting scroll member  58  is a cylindrical hub having a journal bearing  62  therein and in which is rotatively disposed a drive bushing  64  having an inner bore  66  in which crank pin  32  is drivingly disposed. Crank pin  32  has a flat on one surface which drivingly engages a flat surface (not shown) formed in a portion of bore  66  to provide a radially compliant driving arrangement, such as shown in assignee&#39;s U.S. Pat. No. 4,877,382, the disclosure of which is hereby incorporated herein by reference. An Oldham coupling  68  is also provided positioned between orbiting scroll member  58  and bearing housing  24  and keyed to orbiting scroll member  58  and a non-orbiting scroll member  70  to prevent rotational movement of orbiting scroll member  58 . Oldham coupling  68  is preferably of the type disclosed in assignee&#39;s co-pending U.S. Pat. No. 5,320,506, the disclosure of which is hereby incorporated herein by reference.  
         [0034]    Non-orbiting scroll member  70  is also provided having a wrap  72  positioned in meshing engagement with wrap  60  of orbiting scroll member  58 . Non-orbiting scroll member  70  has a centrally disposed discharge passage  74  which communicates with an upwardly open recess  76  which in turn is in fluid communication with a discharge muffler chamber  78  defined by cap  14  and partition  22 . An annular recess  80  is also formed in non-orbiting scroll member  70  within which is disposed a seal assembly  82 . Recesses  76  and  80  and seal assembly  82  cooperate to define axial pressure biasing chambers which receive pressurized fluid being compressed by wraps  60  and  72  so as to exert an axial biasing force on non-orbiting scroll member  70  to thereby urge the tips of respective wraps  60 ,  72  into sealing engagement with the opposed end plate surfaces. Seal assembly  82  is preferably of the type described in greater detail in U.S. Pat. No. 5,156,539, the disclosure of which is hereby incorporated herein by reference. Non-orbiting scroll member  70  is designed to be mounted to bearing housing  24  in a suitable manner such as disclosed in the aforementioned U.S. Pat. No. 4,877,382 or U.S. Pat. No. 5,102,316, the disclosure of which is hereby incorporated herein by reference.  
         [0035]    Referring now to FIG. 3, electrical enclosure  28  includes an electrical case  84 , a compressor protection and control subsystem  86  and a cover  88 . Electrical case  84  is mounted to shell  12  using a plurality of studs  90  (FIG. 2) which are resistance welded to shell  12 . Compressor protection and control subsystem  86  is mounted within electrical case  84  using a pair of mounting screws  92 . Compressor protection and control subsystem  86  is connected to the various components of compressor  10  using wiring which has been omitted from the Figures for purposes of clarity. The connections for compressor protection and control subsystem  86  will be discussed in greater detail below. Compressor protection and control subsystem  86  includes a status display  94  which indicates the status of protection and control subsystem  86  and thus the operating status of compressor  10 . Cover  88  is attached to electrical enclosure  84  using a plurality of screws  98 . Cover  88  defines an aperture  100  which aligns with status display  94  to enable an individual to determine the operating status of compressor  10  without having to remove cover  88 . Status display  94  is capable of displaying numbers and some alpha characters to indicate the various fault codes associated with compressor protection and control subsystem  86 .  
         [0036]    Referring now to FIGS. 4 and 5, a side view of compressor protection and control subsystem  86  is shown in FIG. 4 and a functional block diagram of compressor protection and control subsystem  86  is shown in FIG. 5. Compressor protection and control subsystem  86  includes status display  94  as well as terminals  102  through  136  some of which are connected to internally integrated sensors which are in turn connected to a control block  138 . Terminals  102  and  104  are connected to a high pressure cut off switch  140  and a low pressure cut off switch  142  through an isolated pressure switch sensing monitor  144 . High pressure cut off switch  140  will notify compressor protection and control subsystem  86  of a higher than acceptable pressure reading for compressor  10  and low pressure cut off switch  142  will notify compressor protection and control subsystem  86  of a lower than acceptable pressure reading for compressor  10 .  
         [0037]    Terminal  106  is connected to a pressure sensor  146  which monitors the discharge pressure of compressor  10 . Terminal  108  is connected to a pressure sensor  148  which monitors the suction pressure of compressor  10 . Terminal  110  is connected to a temperature sensor  15   0  which monitors the temperature of the discharge gas of compressor  10 . Terminal  112  is connected to an oil level sensor  152  which monitors the oil level sump  46  of compressor  10 . Input from sensors  146 - 152  are connected to terminals  106 - 112 , respectively, through an analog to digital converter  154  prior to being input to control block  138 .  
         [0038]    Terminals  114 ,  116 , and  118  are connected to a first, a second and a third phase wiring,  156 - 160 , for compressor  10  in order to monitor the status of the three-phase power supply for compressor  10 . Wirings  156 - 160  are connected to control block  138  and terminals  114 - 118  through an isolation and signal conditioner  162 . Terminals  120  and  122  are connected to a group of motor temperature sensors  164  through a PTC Input circuit  166 . Terminal  124  is connected to a compressor control system  168  which indicates that all monitored systems are acceptable and compressor  10  is free to operate.  
         [0039]    Vibration detection can be added to compressor protection and control subsystem  86  by incorporating a preferred vibration sensor  180  within compressor protection and control subsystem  86  as shown in dashed lines in FIG. 4. Vibration sensor  180  is shown in FIGS. 6 and 7 and it comprises a cover  182 , a contractor ring  184 , a terminal rod  186 , a spring wire  188 , a ball  190 , and an end cap  192 . Cover  182  is a generally rectangular shaped plastic component defining a internal circular bore  194 . Contractor ring  184  is fit within an enlarged portion of bore  194  and rests against a shoulder  196  formed by bore  194 . Terminal rod  186  extends through a side wall of cover  182 . Terminal rod  186  is welded to contractor ring  184  such that the end of terminal rod  186  extending through cover  182  can be utilized as a solder point for vibration sensor  180 .  
         [0040]    Spring wire  188  is an L-shaped wire member which has one end of the L extending through the side wall of cover  182  and the opposite end of the L extending axially down the center line of circular bore  194  such that the end of spring wire  188  terminates in approximately the center of contractor ring  184 . Ball  190  includes a radially extending bore  198  which extends from the outer surface of ball  190  to approximately the center of ball  190 . Preferably, ball  190  and spring wire  188  are assembled by inserting spring wire  188  into bore  198  and applying a strong permanent epoxy or by other methods known well in the art. The end of spring wire  188  which extends out of cover  182  is used as a solder point for vibration sensor  180 . End cap  192  is attached to cover  182  by use of a permanent set epoxy which seals bore  194  and thus protects the electrical contacts of vibration sensor  180 .  
         [0041]    Preferably, spring wire  188  is made from spring quality steel or music wire, ball  190  is made form stainless steel (either  302  or  304 ) and contractor ring  184  is made from a seamless  304  stainless steel hollow tubular stock. Contractor ring  184  and ball  190  are preferably plated with gold up to a thickness of 0.000015 inches to prevent oxidation. In the preferred method of fabricating, spring wire  188  and contractor ring  184  are molded in place. Ball  190  is then secure to spring wire  188  and then end cap  192  is assembled.  
         [0042]    Ball  190  and spring wire  188  comprise a simple spring-mass system. Spring wire  188  has the dual purpose of serving as one electrical terminal and also to act as the stiffness member of the spring-mass system. Vibration sensor  180  is located on the circuit board for compressor protection and control subsystem  86  and is most sensitive to vibration in the plane which is perpendicular to the long axis of vibration sensor  180  or the long axis of spring wire  188 . Sensor  180  is actually a form of electrical switch which requires a minimum displacement before the momentary circuit closures or pulses begin to appear. A sensor input network block includes an RC filter which reduces the noise content of the signal.  
         [0043]    In a given orientation, the response of vibration sensor  180  is governed by the stiffness of spring wire  188  and the mass of ball  190 . System response is measured in terms of the amplitude of oscillations of ball  190  when vibration sensor  180  is attached to compressor  10 . In principle, sensor  180  is designed to have a natural frequency close to the operating frequency of compressor  10 . Preferably the natural frequency of sensor  180  is maintained on the higher side of the operating frequency of compressor  10  to eliminate nuisance trips. By controlling parameters such as the stiffness of spring wire  188 , the mass of ball  190  and the gap between ball  190  and contractor ring  184 , it is possible to design sensor  180  to trigger only above a specific value of input vibration. In this context, triggering is said to occur when ball  190  contacts ring  184 . The stiffness of spring wire  188  is a function of the diameter, length and material of spring wire  188 , the mass of ball  190  is a function of its material and its diameter. Thus, by making variations in these parameters, it is possible to change the response curve of sensor  180 . The sensitivity of sensor  180  is determined by the gap between ball  190  and contact ring  184  and how close the natural frequency of sensor  180  is to the operating frequency of compressor  10 . If the two frequencies are close, the system may be over sensitive; i.e. a small change in input vibration amplitude will result in a significant change in output vibration of movement of ball  190 . Similarly, if the two frequencies are far apart, the system may be under sensitive and require a larger input vibration amplitude to cause a small change in output vibration or movement of ball  190 . Computer studies and parallel experimental work has determined that a preferred sensor  180  will trigger at input signal levels of 10-15 mils of input vibration. This preferred design is insensitive to input vibration under 8 mils.  
         [0044]    One issue which needs to be addressed with vibration sensor  180  is it must have the ability to distinguish between a true excessive vibration condition and the normal transient vibrations experienced during start up, flooded start, shut down and the like. Compressor protection and control subsystem module  86  preferably includes a first counter which continuously counts any pulses or triggering that are present using a 10 second time interval. If the number of pulses counted during any 10 second interval exceeds a predetermined number, a limit condition flag is turned on. Conversely, if the number of pulses counted during any 10 second interval is less than a predetermined number, the limit condition flag is turned off. Compressor protection and control subsystem  86  implements a second counter which is an up-down counter. It is clocked by an internal 1 second clock. The counter is limited to 0 counts in the down direction and 120 counts in the up direction. If the condition limit flag is turned on, the counter counts up. If the limit condition flag is turned off, the counter counts down. If at any time the count reaches  120 , control and protection module  86  turns off the control relay and sets status display  94  to indicate a “vibration trip condition”. Recycling of power to compressor protection and control subsystem  86  is required to clear this condition and reset the counter to 0.  
         [0045]    Control block  138  of compressor protection and control subsystem  86  can also be used to control other various and perhaps optional systems incorporated into compressor  10 . Terminal  126  is designed to be connected to a solenoid control system  210  which in turn is connected to an unloading control for a compressor for controlling the capacity of a compressor  214  shown in FIG. 8. Compressor  214  is identical to compressor  10  except for the incorporation of a capacity control system  216  which is controlled by control block  138 .  
         [0046]    Terminal  128  is designed to be connected to a solenoid control system  218  which is, in turn, connected to a liquid injection system  222  for controlling the liquid injection for a compressor  224  shown in FIG. 9. Compressor  224  is identical to compressor  10  except for the incorporation of liquid injection system  222 .  
         [0047]    Terminal  130  is designed to be connected to a solenoid control system  226  which is, in turn, connected to an oil injection system  230  for controlling oil injection for a compressor  234  shown in FIG. 10. Compressor  234  is identical to compressor  10  except for the incorporation of oil injection system  230 .  
         [0048]    Terminal  132  is designed to be connected to a heater control system  236  which is, in turn, connected to a crankcase heater  238  for heating the lubricating oil in sump  46  of compressor  10  as shown in FIG. 1.  
         [0049]    While FIGS. 8-10 each show a separate system added to compressor  10 , it is within the scope of the present invention to include one or more of systems  216 ,  222  or  230  if desired.  
         [0050]    Communication with control block  138  of compressor protection and control subsystem  86  is provided by a communication interface or gateway  250  which communicates with control block  138  through terminals  134  and  136 . DC voltage to power the various sensors is provided a power supply system  252 . Gateway  250  uses Motorola&#39;s Serial Peripheral Interface (SPI) for communicating with bridge or gateway modules. Motorola&#39;s SPI was designed to allow communications between a microcontroller and integrated circuits on a board providing expanded peripheral functions. Another bus, the I 2 C is similar to the SPI and was developed by Signetics/Philips Semiconductor. By using one of these buses, the only hardware required for connection to a pluggable gateway board is a suitable connector. By taking this approach, the system communications protocol is limited only by the gateways made available.  
         [0051]    The SPI and I 2 C are the lowest cost approaches to providing communications and all that is needed is an adapter or a gateway. The preferred embodiment uses a serial interface using RS-485. The protocol used by the advanced compressor control and protection system of the present invention for either the simple SPI-to-gateway communications or in the case of an RS-485 based local network application is a master-slave protocol. The system control is the master when the local RS-485 interface is used. If another protocol is required, the gateway module acts as the master on the compressor control interface side.  
       Node Address Assignments  
       [0052]    There are 32 node addresses to specify the target node. Address  0  is reserved for master broadcast messages. Address  31  is reserved for messages to the bus master. The remaining addresses are available for slave nodes. The Node Address is contained in the five most significant bits of Byte  0 .  
       Message Types  
       [0053]    The message type is contained in the least significant three bits of Byte  0 . Eight message types are defined as follows:  
         [0054]    1. Slave Status Request—This message is used by the system master to interrogate a slave node for its status. The addressed slave responds with one or more Status Reply messages. This message has a packet length of zero (0).  
         [0055]    2. Status Reply—This message is used by slave nodes as a reply to Slave Status Request messages from the system master.  
         [0056]    3. Control Commands—A Command Control message is used to control the actuator outputs of a slave node. Packet zero (0) of this message type is always a single byte and is used as a hardware reset command. All bits set to 1&#39;s generate a hardware reset in the slave node.  
         [0057]    4. Configuration Request—The Configuration Read message is used by the system master to command a slave node to send its configuration data by means of one or more data packets contained in Configuration Data messages. This message has a packet length of zero (0).  
         [0058]    5. Configuration Data—The Configuration Data message is used to send data packets containing the slave node&#39;s configuration data when the slave node has received a Configuration Read message. This is typically data stored in the slave node&#39;s EEROM of Flash Memory storage. It causes information which identifies the node type, serial number, date of manufacture, event histories, etc.  
         [0059]    6. Sensor Read Request—The Sensor Read message is sent by the system master to command the slave node to send its sensor data. This message has a packet length of zero (0).  
         [0060]    7. Sensor Data—This message type is sent by a slave node in response to the Sensor Read message from the system master.  
         [0061]    8. Receipt Response—The Receipt Response message is sent by a slave node in response to messages from the system master which do not require data to be returned. This data packet is always a 1 byte ACK or NAK.  
         [0062]    Packet Number  
         [0063]    A message type may have up to 8 packets. Each packet may be 1 to 32 bytes in length and is sent in a separate message. The first message sent has the packet number set to the number of packets to be sent. Each subsequent message has the packet number decremented. The last message contains the last packet to be sent and is packet number zero (0).  
         [0064]    The packet Number is contained in the most significant 3 bits of Byte  1 .  
       Packet Length  
       [0065]    The Packet Length specifies the length of the Data Packet in each message. The Packet Length is contained in the least significant 5 bits of Byte  1 . Each message contains a data packet with up to 31 data bytes. The only exception is a packet length of zero (0) bytes. In this case there is no data packet in the message.  
       Node Types  
       [0066]    Node definitions can be created for any component in a system that is capable of supporting communications. A good example would be a refrigeration case control. Or if partitioning of the system is desired, node definitions for individual or groups of sensors and actuators would make sense. These definitions would define the specific messages and their content as required for the particular devices. This document release focuses on the compressor node only.  
       Compressor Node  
       [0067]    The compressor node utilizes all message types available. The Configuration data message type 5 is used to transfer the compressor configuration data between the system master and each compressor node. The compressor is shipped with the data preconfigured. The system master may send a Configuration Request to a selected compressor node and get an image of the stored data. It may modify that data or it may construct a completely new image and send it to the compressor for storage by sending it in the appropriate series of Configuration Data packets. Typical configuration variables are listed below.  
       Configuration Data List  
       [0068]    Compressor Information  
         [0069]    Compressor Model Code  
         [0070]    Compressor Serial Number  
         [0071]    Application  
         [0072]    Application Temperature Range  
         [0073]    Refrigerant Code  
         [0074]    Oil Code  
         [0075]    Oil Charge  
         [0076]    Customer Information  
         [0077]    Customer Name  
         [0078]    Customer Model Number  
         [0079]    Control Configuration  
         [0080]    Anti Short Cycle Time  
         [0081]    Discharge Pressure Cut-in  
         [0082]    Discharge Pressure Cut-out  
         [0083]    Discharge Pressure Sensor Option Enabled  
         [0084]    Discharge Trip Time  
         [0085]    Discharge Multiplier  
         [0086]    Discharge Divider  
         [0087]    Discharge Temperature Cut-out  
         [0088]    Oil Add Set Point  
         [0089]    Oil Stop Add Set Point  
         [0090]    Oil Trip Set Point  
         [0091]    Oil On Time  
         [0092]    Oil Off Time  
         [0093]    Oil Add Period  
         [0094]    Shake Limit (pulses/10 second period.)  
         [0095]    Shake Count (number of periods)  
         [0096]    Suction Pressure Low Limit  
         [0097]    Suction Pressure High Limit  
         [0098]    Suction Multiplier  
         [0099]    Suction Divider  
         [0100]    Suction Pressure Sensor Option  
         [0101]    Additional information in the Configuration Data category is certain history information as listed below.  
         [0102]    Event History  
         [0103]    Compressor Cycles  
         [0104]    Compressor On Time  
         [0105]    Discharge Pressure Trips  
         [0106]    Discharge Temperature  
         [0107]    Motor Trips  
         [0108]    Oil Trips  
         [0109]    Suction Pressure Limit Trips  
         [0110]    Shake Limit Trips  
         [0111]    Events Since Cleared  
         [0112]    Using the above described protocol, some typical sensor data which would be sent in response to a sensor data request would be as detailed below.  
         [0113]    Anti Short Cycle Time—32 bit unsigned (mS)  
         [0114]    Discharge Pressure Cut-in—32 bit signed (up to 6553.5 kPa, res. 0.1 kPa)  
         [0115]    Discharge Pressure Cut-out—32 bit signed (up to 6553.5 kPa, res. 0.1 kPa)  
         [0116]    Discharge Trip Time—16 bit unsigned (res. 0.01 S)  
         [0117]    Discharge Multiplier—32 bit unsigned  
         [0118]    Discharge Divider—32 bit unsigned  
         [0119]    Suction Pressure Cut-in—32 bit signed (+,−3276.7 kPa, res. 0.1 kPa)  
         [0120]    Oil Stop Add—16 bit unsigned  
         [0121]    Suction Pressure Cut-out—32 bit signed (+,−3276.7 kPa, res. 0.1 kPa)  
         [0122]    Suction Multiplier—32 bit unsigned  
         [0123]    Suction Divider—32 bit unsigned  
         [0124]    Oil Add—16 bit unsigned  
         [0125]    Oil Trip—16 bit unsigned  
         [0126]    Oil On Time—32 bit unsigned (mS)  
         [0127]    Oil Off Time—32 bit unsigned (mS)  
         [0128]    Oil Add Period—16 bit unsigned (0.01 S)  
         [0129]    Vibration Limit—16 bit unsigned—pulses/10 s  
         [0130]    Vibration Count—8 bit unsigned—10 s periods  
         [0131]    Referring now to FIG. 11, compressor  10  is illustrated showing the Serial Peripheral Interface (SPI) for connecting compressor protection and control subsystem  86  of compressor  10  to a central control system  254 . Using the SPI interface and the gateway, subsystem  86  of compressor  10  can be controlled by and communicate with a master network. The connection and communication with the master network is preferably through LonWorks but other network connections such as SPi, CANBus, Device Net, Internet/intranet, BAC net or a Proprietary connection can be established. FIG. 12 illustrates the network system when a centralized rack gateway  256  is utilized to communicate with a group of compressors  10 , FIG. 13 illustrates the network system when a rack/system control  258  acts as the gateway for communicating with a group of compressors  10  and FIG. 14 illustrates the network system when an Internet web server  260  or a local Intranet server  262  is utilized to communicate with individual Ethernet gateways associated with each compressor  10 .  
         [0132]    One problem associated with the development of the advanced compressor control and protection system was an accurate oil level sensor applicable to compressors. The requirements for the sensor included that it have no moving parts, that it be compatible with the environment of the interior of the compressor in the sump and that its costs be competitive with current day float based sensors. Two concepts were deemed to have merit. First, self-heated thermistor with temperature compensation had the potential to be simple, reliable and low cost and second, capacitance was considered as a potentially reliable, accurate and low cost approach as well.  
         [0133]    A capacitance based sensor  300  shown in FIG. 15 is one option for an oil sensor. There is a large enough dielectric constant of oil versus refrigerant gas to be able to derive a usable signal. The volume construction of such a device having a consistent capacitance from unit to unit without calibration is feasible if the electrodes are arranged coaxially. Sensor  300  is comprised of a hollow stainless tube  302  with a small coaxially positioned rod  304 .  
         [0134]    A multiple thermocouple liquid level sensor  320  is shown in FIG. 16. Sensor  320  comprises an unevenly heated thermocouple array  322 . Sensor  320  requires a compensation for the effect of different gas densities by using a separate unevenly heated thermocouple pair which is always disposed within the suction gas of the compressor. A mathematical model was developed using the output from the thermocouple disposed in the gas to correct the output of the thermocouple disposed in the lubricant for variation pressure and temperature of the suction gas over the compressor&#39;s operating envelope.  
         [0135]    Referring now to FIG. 17, a system schematic for a compressor protection and control subsystem  86 ′ for use with a semi-hermetic rotary compressor is disclosed. Subsystem  86 ′, shown in FIG. 17, is similar to subsystem  86  shown in FIG. 5 except for the addition of control for an oil switch  300 . A semi-hermetic rotary compressor is similar to a hermetic rotary compressor except that the shell for the semi-hermetic rotary compressor is bolted together rather than being welded as shown for shell  12 . in addition, the semi-hermetic rotary compressor is typically equipped with a positive displacement lubricant pump which maintains an oil pressure within the lubrication system for the semi-hermetic rotary compressor. A pressure sensor monitors the pressure for the lubrication system with the pressure sensor communicating with control block  138  through a pair of terminals  302  and  304 . Logic within control block  138  monitors the lubrication after lubrication pressure is determined to be low or inadequate for a specified period of time. The time delay used for controlling the compressor for a lack of sufficient oil pressure avoids problems associated with mis-trips caused to varying oil pressure. The function and operation of the remainder of compressor protection and control subsystem  86 ′ is the same as that described above for compressor protection and control subsystem  86 .  
         [0136]    While the above detailed description describes the preferred embodiment of the present invention, it should be understood that the present invention is susceptible to modification, variation and alteration without deviating from the scope and fair meaning of the subjoined claims.