CMC Peer-to-Peer Control System Software. User s Manual Version 1.0

Transcription

1 CMC Peer-to-Peer Control System Software User s Manual Version 1.0

2 Rev. 03 Date of Issue: 6/12/07

3 PREFACE Information and Illustrations Information and illustrations are not binding. Ingersoll-Rand Company reserves the right to make changes to its products. Trademarks All terms used in this publication to denote Ingersoll-Rand Company products are trademarks of Ingersoll-Rand Company. All other terms used in this publication to denote products may be registered trademarks and/or trademarks of the corresponding corporations. Belden is the registered trademark of Belden Wire and Cable Company. Copyright All rights are reserved. This document may not be reproduced or transmitted in any form or by any means without permission in writing by Ingersoll-Rand Company. The user is not authorized to translate this document into any other language Ingersoll-Rand Company. All rights reserved Rev. 03 Date of Issue: 6/12/07 3

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5 TABLE OF CONTENTS 1.0 OVERVIEW Control description REQUIREMENTS system requirements operation overview Security NETWORK WIRES Panel to Panel RS-485 connection Ethernet Side (Optional) Modbus to Ethernet Bridge Local Panels INSTALLATION Prework USING THE SOFTWARE Peer-to-peer Control Screens Status Page Local Enable / Disable Page Pressure Setpoints / Sequence Page System Enable / Disable Page Loadsharing Page Alarms / Communication Page Event Log Page Control States Communications MODBUS Communications Direct CMC Communications with RS422/ SYSTEM CONTROL Sequencing voting Group Membership and communications monitoring Communications Failure Modes Control Logic Theory Machine control of Centrifugal Compressors Pressure Limits Time Limits Automatic Loading Automatic Starting Automatic Unloading Automatic Stopping Loadsharing of Centrifugal Compressors Anti-Blowoff Inlet Valve Load-Sharing APPENDIX A: glossary Rev. 03 Date of Issue: 6/12/07 5

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7 1.0 OVERVIEW 1.1 CONTROL DESCRIPTION Peer-to-Peer Control is software specifically developed for automatic pressure control of air compressor systems. The primary goal of this software is to monitor and control the compressed air system and optimize its operation. Peer-to-Peer Control provides energy management through load sharing and reduction of air by using the minimum amount of energy to meet the system demand. It utilizes an RS-485 serial network, and specially designed CMC software to provide a powerful yet user-friendly air system control solution. Peer-to-Peer Control provides automatic control of a group of compressors with no PC or PLC required for control. It offers the ability to: Sequence a group of compressors Start compressors when needed Load compressors Perform Load-sharing (Anti-Blow-off) Perform Unload Tests to determine when compressors can be taken off line Unload compressors when unload test passes Stop compressors when timers allow Start / load a compressor after a loaded compressor trips, with no delay timer Participation in Peer-to-Peer Control: start, load, unload test, unload, and stop functions are individually enabled / disabled through each compressors local control panel. Load sharing, start / load / unload / stop, and start-after-trip are enabled / disabled for all compressors from any local control panel. The system size is limited to 4 compressors, operating in a single pressure system, with single board (BCM) local control panels. Figure 1-1: Peer-to-Peer Control Architecture Overview CMC Panel CMC Panel CMC Panel CMC Panel CENTAC Microcontroller CENTAC Microcontroller CENTAC Microcontroller CENTAC Microcontroller Base Control Module (BCM) RS-232 Network for OUI Base Control Module (BCM) RS-232 Network for OUI, Base Control Module (BCM) RS-232 Network for OUI, Base Control Module (BCM) RS-232 Network for OUI, Panel Address: ohm Panel Address: 2 Panel Address: 3 Panel Address: ohm IRBUS (RS-485) Network for Base Control Modules, Twisted Pair Wires with Ground (3 Wires) IRBUS (RS-485) Network for Base Control Modules, Twisted Pair Wires with Ground (3 Wires) IRBUS (RS-485) Network for Base Control Modules, Twisted Pair Wires with Ground (3 Wires) Rev. 03 Date of Issue: 6/12/07 7

8 2.0 REQUIREMENTS 2.1 SYSTEM REQUIREMENTS Items required for Peer-to-Peer Control to function are listed here. CMC panel must have version 3.0 hardware. CMC version 3.2 code must be installed in the BCM. Communications between panels, and with the service tool will use the IRbus v3 protocol. All panels in the group must have the Peer-to-Peer Control code module loaded. All panels in the group must have the Energy Management code module loaded. All panels in the group must have a remote communications selector switch. When Peer-to-Peer Control is active, member compressors must operate in Modulate mode. The remote communications enabled light on the panel door shows when the system is enabled. BCM addresses must be configured to be (panel-bcm) 1-1, 2-1, 3-1, or 4-1. This is done using the service tool if changes are necessary. Panels are to be connected with the RS485-IRBus. 120 ohm terminating resistors are required at each end of the RS485 cabling. 2.2 OPERATION OVERVIEW The Peer-to-Peer Control code is disabled by default, and must be turned on at each panel to allow the logic to become active. The Peer-to-Peer Control logic will be disabled by any trip event on the local compressor, and must be re-enabled by the user after clearing the trip. One or more compressors can be removed from the group without causing automatic control to be disabled. A compressor can be added to the group without disabling automatic control. The group of compressors will automatically recognize new members of the group. Changes to the system set-points can be made on any OUI and are transmitted to the whole group. These settings will be shared with the group whether or not the Peer-to-Peer Control logic is enabled. All shared data is transmitted at the time it is changed by the user. A machine is considered to be a new member by the group until all the shared settings have been received from the group or the user changes the settings on the new member s OUI (thus sending it s settings to the group). All shared data is re-transmitted when a new member of the group is recognized. A new member of the group will not transmit shared settings unless the user changes the settings on the new member s OUI. All members of the group will transmit shared status information. A new member cannot participate in Start / Load / Unload / Stop actions Rev. 03 Date of Issue: 6/12/07

9 2.3 SECURITY Ingersoll Rand Self Control User's Manual Access to modify Peer-to-Peer Control system settings from the CMC faceplate requires the operator to enter the password on page 1 of the SETTINGS tab. 2.4 NETWORK WIRES Panel to Panel RS-485 connection Cabling for the RS-485 BCM interconnection network must be single pair shielded cable that meets or exceeds Belden The maximum distance on the RS-485 network is 4000 electrical feet from first to last panel connection. Figure 2-1: Belden 9841 Cable Data Figure 2-2: Belden 9841 Cable Ethernet Side (Optional) Wiring the network is accomplished by connecting to the optional Bridge using Category 5 (or better) cables. If the Bridge will be connected to a network consult the LAN administrator to determine if a crossover cable is required. Figure 2-3: Crossover Schematic white/green 2 1 RJ-45 green RJ Top Side white/orange blue white/blue orange white/brown Bottom Side brown Rev. 03 Date of Issue: 6/12/07 9

10 Figure 2-4: RJ-45 Plug The Ethernet cables are terminated with CAT 5 RJ-45 modular plugs. RJ-45 plugs are similar to those seen on the end of a telephone cable except they have eight versus four or six contacts on the end of the plug and they are about twice as big. (RJ means "Registered Jack"). Some RJ-45 plugs are designed for both solid core wire and stranded wire while others are designed specifically for one kind of wire. Use plugs appropriate for the wire that will be used. 2.5 MODBUS TO ETHERNET BRIDGE As CMC panels equipped with the optional UCM utilize Modbus protocol, the Modbus to Ethernet Bridge provides a means for transacting messages between Ethernet TCP/IP devices and Modbus serial devices. An optional bridge can be furnished in a separate NEMA 12 box with its own power supply. A / VAC, 60/50 Hz power source is required. There are a number of devices on the market to choose from when selecting a bridge. One such device is the 174 CEV Modicon TSX Momentum Modbus to Ethernet Bridge. This bridge will be supplied and configured by an Ingersoll-Rand Service Technician to match your system application if required. 2.6 LOCAL PANELS CMC Panels Communication to all air compressors shall be accomplished using Ingersoll-Rand microcontroller panels. Local panels must be CMC as manufactured by Ingersoll-Rand Company. CMC panels must be fitted with a Remote Communications selector switch. The Remote Communications switch must be in the Enabled position before Peer-to-Peer Control will function. A UCM is not required for Peer-to-Peer Control operation Rev. 03 Date of Issue: 6/12/07

11 3.0 INSTALLATION 3.1 PREWORK Before the Service Technician begins to commission the Peer-to-Peer Control, the following items should be completed. 1) RS-485 Interconnection network cables pulled and terminated. 2) 120-ohm terminating resistors are required at each end of the RS485 cabling. 3) System components should be operational. 4) Route the network wire in its own grounded conduit. 5) If remote communications is being utilized, a single UCM must be configured for operation. 6) If the Modbus to Ethernet bridge is being utilized for Ethernet communications, the bridge must be configured for operation. Figure 3-1: Peer-to-Peer Control Architecture Overview CMC Panel CMC Panel CMC Panel CMC Panel CENTAC Microcontroller CENTAC Microcontroller CENTAC Microcontroller CENTAC Microcontroller Base Control Module (BCM) RS-232 Network for OUI Base Control Module (BCM) RS-232 Network for OUI, Base Control Module (BCM) RS-232 Network for OUI, Base Control Module (BCM) RS-232 Network for OUI, Panel Address: ohm Panel Address: 2 Panel Address: 3 Panel Address: ohm IRBUS (RS-485) Network for Base Control Modules, Twisted Pair Wires with Ground (3 Wires) IRBUS (RS-485) Network for Base Control Modules, Twisted Pair Wires with Ground (3 Wires) IRBUS (RS-485) Network for Base Control Modules, Twisted Pair Wires with Ground (3 Wires) Rev. 03 Date of Issue: 6/12/07 11

12 4.0 USING THE SOFTWARE 4.1 PEER-TO-PEER CONTROL SCREENS Status Page Status area Shows the number of compressors with Peer-to-Peer enabled, and in P2P alarm status. A Member Alarm will show if both are active. A P2P comm alarm will cause the status area to show alarm, and put a message in the event log specifying which machine is not communicating well. A P2P member alarm will cause the status area to show alarm, and put a message in the event log. Average Press area Shows the number of machines included in the average, the type of average ( All, Running, Loaded ), and the average pressure which Peer to Peer Control will use in its control decisions. Comp Column - Checkbox indicates member status, and Compressor addresses are in sequence order (top to bottom). Status column Displays the status of each compressor ( Not Ready, Ready, Unloaded, Loaded, Changing ). Pressure Column Displays the system pressure reading from each compressor. Figure 4-1: Status Page Rev. 03 Date of Issue: 6/12/07

13 4.1.2 Local Enable / Disable Page Ingersoll Rand Self Control User's Manual Each of these values enables the individual compressor only: Enable participation in P2P - Must be set to allow this machine to take part in the Peer-to-Peer Control activities. If this compressor trips for any reason, this will be disabled automatically. Allow P2P to start compressor - Must be checked to allow this machine to be started automatically by Peer-to-Peer Control. Allow P2P to load compressor - Must be checked to allow this machine to be loaded automatically by Peer-to-Peer Control. Allow P2P to unload compressor - Must be checked to allow this machine to be unloaded automatically by Peer-to-Peer Control. Allow P2P to stop compressor - Must be checked to allow this machine to be stopped automatically by Peer-to-Peer Control. Figure 4-2 Local Enable / Disable Page Rev. 03 Date of Issue: 6/12/07 13

14 4.1.3 Pressure Setpoints / Sequence Page Current P2P Sequence - This is the currently entered sequence for reference while making changes. New P2P Sequence - This is where a new sequence is entered. Each number 1-4 can only be used once. Apply new sequence - Check this after entering all of the compressor numbers into the New P2P Sequence. This box will revert back to unchecked immediately. Once this is set, the new sequence will be validated and applied. If this new sequence is invalid it will be replaced by the current sequence. P2P Unload/Stop Pressure - When the average pressure is above this setting, Peer-to-Peer Control will want to unload or stop a compressor. Refer to sections and for more information about auto unloading and auto stopping. P2P Target Pressure - This is the substitute setting used when Peer-to-Peer Control is active. This setting overwrites System Pressure Setpoint when Peerto-Peer Control is enabled. P2P Load/Start Pressure - When the average pressure is below this setting, Peer-to-Peer Control will want to load or start a compressor. Refer to sections and for more information about auto loading and auto starting. Figure 4-3: Pressure Setpoints / Sequence Page Rev. 03 Date of Issue: 6/12/07

15 4.1.4 System Enable / Disable Page Ingersoll Rand Self Control User's Manual Enable P2P Start/Load/Unload/Stop - Checking this enables the Peer-to-Peer Control start / stop / load / unload functions. Refer to section 5.6 Enable P2P Load-sharing - Checking this enables the Peer-to-Peer Control to control anti-blow off. Refer to section 5.7 Enable immediate start/load after P2P member trip - Checking this enables Peer-to-Peer Control to bypass the start, load, and wait timers in the event of a member compressor tripping off line while running loaded. All the above values on this page are shared among all the members in the system. A change here will appear on all similar screens almost instantly. Minimum Run Timer - This setting (seconds) determines the minimum amount of time a compressor must run before Peer-to-Peer Control will be allowed to stop it. An automatic stop will not occur while this timer is running. The timer starts any time the compressor starts (including manual starts). This timer must be adjusted on each individual panel. Figure 4-4: System Enable / Disable Page Rev. 03 Date of Issue: 6/12/07 15

16 4.1.5 Loadsharing Page Total Bypass This is the sum of all member compressor bypass valves. Allowed Bypass This setting is the amount of bypass allowed in the system before unloading a compressor. Refer to section for more detail about Allowed Bypass settings. Anti Bypass Gain - This setting encourages the compressors to share the load. Refer to section for more detail about making Anti Bypass gain settings. Inlet Valve Gain This setting encourages compressors in the system to distribute the load more evenly. Refer to section for more detail about making Inlet Valve gain settings. Unld Test Rate This setting controls the rate at which the unload test lowers the compressor s setpoint during an unload test. Refer to section for more detail about the unload test. Unld Test BV Max This setting is the position the bypass valve must reach before the unload test will pass. Refer to section Wait Timer - This setting is the length of time Peer-to-Peer Control will wait after a start / stop / load / unload before doing anything else. Refer to section Start Delay Timer - This setting is the delay before starting a compressor after the pressure goes below the start / load pressure. Refer to section Load Delay Timer - This setting is the delay before loading a compressor after the pressure goes below the start / load pressure. Refer to section Unload Delay Timer - This setting is the delay before starting an unload test after the pressure goes above the unload / stop pressure. Refer to section Stop Delay Timer - This setting is the delay before stopping a compressor after the pressure goes above the unload / stop pressure. Refer to section All values on this page are shared among all the members in the system. A change here will appear on all similar screens almost instantly Rev. 03 Date of Issue: 6/12/07

17 Figure 4-5: Loadsharing Page Ingersoll Rand Self Control User's Manual Alarms / Communication Page Low Member Count Alarm - If the number of participating members in Peer-to- Peer Control falls below this setting, the member alarm will be set. Communications Problem Alarm - If the communications count for any compressor falls below this setting, that panels alarm will be set. Comp Column - This column shows the compressors in address order. Communications column - This is the communications status for the compressor. Refer to sections 5.3 and 5.4 for more detail about communications monitoring and failure modes indicates perfect or near-perfect communications 9-7 indicates some communications errors 7-1 indicates poor communications 0 indicates no communications Rev. 03 Date of Issue: 6/12/07 17

18 Figure 4-6: Alarms / Communication Page Event Log Page P2P Enabled - This event occurs when the Enable participation in P2P checkbox is checked. Reference figure 4-2 P2P Disabled by User - This event occurs when the Enable participation in P2P checkbox is unchecked by the user. Reference figure 4-2 P2P Disabled by Trip - This event occurs when the Enable participation in P2P checkbox is unchecked because of any CMC trip. P2P Control Enabled - This event occurs when the Enable P2P Start/Load/Unload/Stop checkbox is checked. Since this is a shared value, all CMC s on the Peer-to-Peer Control network will show this event. Reference figure 4-4 P2P Loadsharing Enable - This event occurs when the Enable P2P Loadsharing checkbox is checked. Since this is a shared value, all CMC s on the Peer-to-Peer Control network will show this event. Reference figure 4-4 P2P Control Disabled - This event occurs when the Enable P2P Start/Load/Unload/Stop checkbox is unchecked. Since this is a shared value, all CMC s on the Peer-to-Peer Control network will show this event. Reference figure Rev. 03 Date of Issue: 6/12/07

19 P2P Loadsharing Disable - This event occurs when the Enable P2P Loadsharing checkbox is unchecked. Since this is a shared value, all CMC s on the Peer-to-Peer Control network will show this event. Reference figure 4-4 P2P Member Count Low - This event occurs when the x in comm drops below Low Member Count Alarm. Since this is based on shared values, all CMC s on the Peer-to-Peer Control network will show this event. Reference figure 4-3 and 4-6. P2P Comm Alarm for 1 - This event occurs when the Communications value for compressor 1 drops below the Communications Problem Alarm Level. Since this is based on shared values, all CMC s on the Peer-to-Peer Control network will show this event. Reference figure 4-6 Reset (P2P) This even occurs when the user presses the reset button on the OUI. This action will reset all alarms and trips on that machine including P2P alarms. Because P2P shares the reset flag with the other P2P machines, this event will appear on all P2P machines OUI s - possibly several times since the reset flag is re-transmitted by each controller. NOTE: P2P alarms are the only alarms that are cleared on more than one machine. All other alarms/trips not related to P2P must be reset at each machine. In the event of an alarm or trip, you will be taken to the alarm and trip log for that panel. Any alarm or trip must be acknowledged on the local panel by depressing the Acknowledge pushbutton. Figure 4-7: Event Log Page Rev. 03 Date of Issue: 6/12/07 19

20 4.2 CONTROL STATES Compressor Ready, Running, Unloaded, and Loaded are the Peer-to-Peer Control states. The state here is different than the normal compressor state since Peer-to-Peer Control doesn t care if it is maxload or minload etc. This means the list of possible control states is much simpler. Also in Peer-to-Peer Control, any time the compressor is transitioning from one state to another, the Peer-to-Peer Control Status page status column will display the state as Changing. This includes compressor states such as loading, coasting, waiting, etc Rev. 03 Date of Issue: 6/12/07

21 4.3 COMMUNICATIONS Ingersoll Rand Self Control User's Manual Communication to a Peer-to-Peer Control system has been designed so that a single UCM can be used to interface a customers data acquisition / control system and all the CMC panels in the Peer-to-Peer network. Your IR Service Technician will configure the UCM during commissioning of the Peer-to-Peer Control system. Figure 4-8: Control Communications Architecture Overview CMC Panel CMC Panel CMC Panel CMC Panel Auxiliary Panel Microcontrol CENTAC? ler Microcontrol CENTAC? ler Microcontrol CENTAC? ler Microcontrol CENTAC? ler 120/240 VAC Power Base Control Module (BCM) RS-232 Network for OUI Base Control Module (BCM) RS-232 Network for OUI, Base Control Module (BCM) RS-232 Network for OUI, Base Control Module (BCM) RS-232 Network for OUI, Customers Network Universal Communications Module (UCM) 24 VDC Power Supply Panel Address: ohm Panel Address: 2 Panel Address: 3 Panel Address: ohm 24 VDC IRBUS (RS-485) Network for Base Control Modules, Twisted Pair Wires with Ground (3 Wires) IRBUS (RS-485) Network for Base Control Modules, Twisted Pair Wires with Ground (3 Wires) IRBUS (RS-485) Network for Base Control Modules, Twisted Pair Wires with Ground (3 Wires) IRBUS (RS-485) Network for Base Control Modules, Twisted Pair Wires with Ground (3 Wires) MODBUS Communications Customers may want to communicate to the CMC control systems for remote compressor control and monitoring. This communication capability provides for flexibility in the customer's compressed air operation through remote start and stop, data gathering for preventative maintenance, and incorporation into plant-wide control system. The major avenue for communicating with the CMC is via MODBUS protocol over an RS422/485 hardware link. This requires hardware for the control panel, and a communications device with the appropriate driver software to perform the desired panel functions. The RS422/485 interface can communicate with any serial device that has an RS422 or RS485 port. The customer or his representative must write system software to suit his individual needs for remote control and monitoring. Since the customer writes this interface, the system can be as flexible as the customer desires Rev. 03 Date of Issue: 6/12/07 21

22 Refer to the table below for MODBUS Absolute Addresses for each Holding Register supported by the CMC-MODBUS interface. Holding Register Name Read / Write OUI Location (Page number in Peer2Peer Tab) Signed 16 bit Integer Absolute Address (Decimal) Signed 16 bit Fraction Absolute Address (Decimal) NodeIDPanel 1, SC_Member_Count SC_Alarm_Status SC_Average_Pressure SC_Avg_Size SC_Avg_Type SC_Enable SC_Start_Enable SC_Load_Enable SC_Unload_Enable SC_Stop_Enable SC_New_Sequ SC_UnloadStopPressure SC_PSP SC_StartLoadPressure SC_Timer_Minrun SC_SLUS_Enable SC_Loadshare_Enable SC_TripStartVote_Enable SC_ABG SC_Timer_Waiting SC_Timer_StartLoad SC_Timer_Load SC_Timer_Unload SC_Timer_Stop SC_Reset SC_MinMember_Alarm SC_CountAlarm SC_IVG SC_Total_Bypass SC_Allowed_Bypass SC_Seq[1] SC_Seq[2] SC_Seq[3] SC_Seq[4] SC_New_Seq[1] SC_New_Seq[2] SC_New_Seq[3] SC_New_Seq[4] SC_Counter[1] SC_Counter[2] SC_Counter[3] SC_Counter[4] SC_OUI_Seq[1] SC_OUI_Seq[2] SC_OUI_Seq[3] SC_OUI_Seq[4] SC_OUI_Press[1] SC_OUI_Press[2] SC_OUI_Press[3] SC_OUI_Press[4] SC_OUI_Status[1] SC_OUI_Status[2] SC_OUI_Status[3] SC_OUI_Status[4] Signed IEEE 32-bit Float Absolute Address (Decimal) Rev. 03 Date of Issue: 6/12/07

23 4.3.2 Direct CMC Communications with RS422/485 Ingersoll Rand Self Control User's Manual There are many ways of interfacing from CMC control systems to a serial device through an RS422/485 port. A serial device can be a Personal Computer (PC), Programmable Logic Controller (PLC), Distributed Control System (DCS) or any other device that can transmit, receive and interpret an RS422/485 formatted signal over a hardware link. All RS422/485 interfaces require custom interface software and custom application software. The interface software allows a specific serial device and operating system to transmit, receive and interpret data from a CMC control system. The application software tells the CMC control system what to do; for example, start compressor when ready, stop compressor after midnight and retrieve the current data and save to a disk file. Currently there are hundreds of different serial devices using different operating systems and languages in the industrial equipment world. Therefore, the practicality of having an interface for many systems is limited. Custom interfaces must be written as required by the hardware and operating system used. The only limits of the application software are the capabilities of the hardware and the imagination of the developer. The developer may write functions to read and display data, log that data to some magnetic media for storage, change compressor set points, and network additional devices, such as pumps, dryers, etc., into the system. All of these functions require specially written application software for the intended use. Refer to the CMC Technical Reference Manual sections titled Communication and The CMC-MODBUS Interface for a detailed how-to on reading from / writing to CMC panels Rev. 03 Date of Issue: 6/12/07 23

24 5.0 SYSTEM CONTROL This section will describe how Peer-to-Peer Control will operate CMC equipped compressors. Italicized terms will indicate setpoints that have an effect on this behavior. In order to understand the control methodology sequencing must first be considered. 5.1 SEQUENCING Definition: Selecting the order in which Peer-to-Peer Control auto starts / loads / unloads / stops and performs unload tests on the compressors. Peer-to-Peer Control must be enabled for the compressor to be included in the sequence. If Peer-to-Peer Control is enabled on each local CMC panel, that compressor is included in the Member Count list of how many compressors are being controlled by Peer-to-Peer Control, and is included in the sequence. 5.2 VOTING Operation of the Peer-to-Peer Control system depends on good communications. Because of the possibility of communications errors and other planned for events, a voting process helps Peer-to-Peer Control decided on what actions to take. This helps decision-making errors less likely to occur. The vote consists of three bits included in the data shared over the network. There is a bit for the start / load vote, unload / stop vote, and start after trip vote. Each compressor determines the value of these bits by running the shared information from the system of compressors through the logic that governs how Peer-to-Peer Control behaves. Since each compressor operates from the same rules, and in theory each compressor has all the same information, the vote should always be unanimous. But if communications errors have occurred and one or more compressors don t have good data, the vote will not be unanimous and no action will be taken until successful communications are restored, and the vote becomes unanimous. This voting behavior is where Peer-to-Peer Control gets its name. All compressors are equal peers and there is no master controller. Also, by having no designated master, it doesn t disrupt the control of the system if a compressor is taken offline for maintenance or because of trouble. The remaining Controlled compressors will continue to try and maintain the target pressure. Here is a summary of the rules used to determine what action Peer-to-Peer Control takes. A Start / Load vote will result from Average Pressure being below the Start / Load Pressure. An Unload / Stop vote will result from Average Pressure being above the Unload / Stop Pressure. The voting must be unanimous before an event will occur Rev. 03 Date of Issue: 6/12/07

25 Once the voting is unanimous, the compressor determined by the sequence and the vote will act by starting it s appropriate timer, wait for the timer to complete, and perform the action (Start, load, unload/test, stop). If the vote becomes non-unanimous after the timer has begun, the action is canceled (with no wait timer). Once the voting has remained unanimous, and the action is complete, all machines will start their own copy of the wait timer. It is not necessary to distinguish between load and start since the logic is programmed to load first then start. So with a sequence of 1,2,3,4, if the next compressor to start is 2 and next compressor to load is 1 then when the start / load vote becomes unanimous, machine 1 will load (after the load timer expires). If there are no compressors running unloaded when the vote becomes unanimous then compressor 2 would start and load (after the start timer expires). 5.3 GROUP MEMBERSHIP AND COMMUNICATIONS MONITORING Because the Peer-to-Peer Control depends so heavily on good communications, it must keep watch for communication problems, and make sure it only includes information from properly communicating members in system controlling decisions. The Peer-to-Peer logic monitors the communications from each compressor and maintains an indicator of each compressors communications success. This indicator tells the Peer-to-Peer Control logic when a new compressor is added to the system, when a compressor has left the system, and when there are communications problems with a compressor. Ref. Fig 4-6 A new compressor is detected when it s communication monitor changes from 0 to 1 or more. It then becomes included in the Member Count, and this also triggers the existing members to send the existing Peer-to-Peer setpoints to the new member. If a member compressor s power is turned off or there is a communications problem, the other compressors will see its monitor value start to drop. Once it falls below the Communications Problem Alarm Level each remaining active member will generate an event log entry showing the address of the compressor that has been removed or is having communications problems. If enough members are disconnected or turned off, so that the number of members falls below the Low Member Count Alarm Level, each remaining active member will generate an event log entry showing that this has occurred. When this occurs, Peer-to-Peer Control will be disabled. If a compressor has a trip of any kind, Peer-to-Peer Control will be disabled for that compressor. If automatic control is disabled the machine will not participate in the group, but will continue to receive settings and send out it s status message Rev. 03 Date of Issue: 6/12/07 25

26 5.4 COMMUNICATIONS FAILURE MODES Suppose you have a Peer-to-Peer Control system operating four compressors. Now suppose the network cable is cut between panel 2 and 3. If the break in the network doesn t short out the 1,2 side of the network, then they will continue to operate automatically as a system of 1,2 only. If the break does short out the1,2 side of the network, then they will revert back to independent control 30 seconds after the break. If the break in the network doesn t short out the 3,4 side of the network, then they will continue to operate automatically as a system of 3,4 only. If the break does short out the 3,4 side of the network, then they will revert back to local control 30 seconds after the break. If control power is lost or the network is disconnected to one or more panels, the remaining panels will continue to operate as a system without the failed panel(s). If the RS485 Network is wired improperly, the entire network will fail because of the wiring error. If problems occur due to low communications signal status, check the wiring connections, verify terminating resistors are installed, and make sure wire lengths are within maximum limits. 5.5 CONTROL LOGIC THEORY There is no "Master" or "Lead" machine. Each machine will calculate the average pressure from the shared pressure readings and status information. The machine will base all group actions on the Average Pressure and other shared information. Average pressure is calculated by the following methods: If compressors are running loaded, Peer-to-Peer Control calculates the average pressure of the loaded machines. If compressors are running, but not loaded, Peer-to-Peer Control calculates the average pressure of the running machines. If there are no compressors running, Peer-to-Peer Control calculates the average pressure from all the members present in the system. The Peer-to-Peer Control auto stop function will be disabled while the minimum run timer is running Rev. 03 Date of Issue: 6/12/07

27 5.6 MACHINE CONTROL OF CENTRIFUGAL COMPRESSORS Ingersoll Rand Self Control User's Manual Definition: Functionality that selects the compressor to load, start, unload, and stop as well as executing the function. There are several settings that must be defined before the functions of machine control can be explained. These settings are: Start/ Load Pressure Start Delay Load Delay Wait Timer Target Pressure IV Load-sharing Gain Anti Bypass Gain Unload/Stop Pressure Unload Delay Stop Delay Allowed Bypass Unload Test Pressure Unload Test Rate Total Bypass Each of these will be explained in the following pages. There are some basic rules that apply when describing automatic machine control. These basic rules are: If a compressor is running unloaded, that compressor will be loaded before another is started. If a compressor is running unloaded, that compressor will be stopped before another is unloaded. Compressors load and start as needed beginning from the left of the list. Compressors unload and stop as needed beginning from the right of the list. A compressor is a candidate for loading or stopping if it is running and in the unloaded state (Unloaded, or Autodual Unloaded). A compressor is a candidate for starting if it is in a ready state (Ready). A compressor is a candidate for unloading if it is running and in a loaded state. To understand the settings that make possible automatic machine control function, an understanding of the air system Pressure Limits is necessary. Not only must Pressure Limits be considered Time Limits must also be considered Rev. 03 Date of Issue: 6/12/07 27

28 5.6.1 Pressure Limits To maintain a desirable operating pressure in the system it is necessary to input a set point in the compressor s pressure controller. For the purpose of this explanation that setpoint will be referred to as Target Pressure. The Target Pressure overwrites the Pressure Setpoint when Peer-to-Peer Control is enabled. Any changes to the system pressure must be made to Target Pressure instead of Pressure Setpoint as long as Peer-to-Peer Control is active. When the Target pressure is changed it is transmitted to all compressors in the Peer-to-Peer system. The Target Pressure (100 in this example) is indicated on the next graph. Figure 5-1: Example of Air System Typically, the air system has a pressure window in which it operates; a pressure not to exceed and a pressure not to go below. By design the pressure controller should limit the rise in system pressure, regardless of the number of machines running. The results will not necessarily be very efficient as some or all the compressors could be bypassing air to the atmosphere. The pressure controller cannot prevent a pressure from going low if enough compressors are not on line. Upon this premise the need for automatic control is realized. With automatic machine control, an increase in pressure above a certain level marks the time to evaluate if a compressor may be unloaded or stopped. At a lower pressure level it is usually suitable to not do anything, as pressure is acceptable. At an even lower level it is time to evaluate if a compressor may be loaded or started. Graphically, this is illustrated below: Rev. 03 Date of Issue: 6/12/07

29 Figure 5-2: Example of Air System Ingersoll Rand Self Control User's Manual After we consider pressure limits we can now consider the first two set points necessary for automatic machine control that is Start/ Load Pressure and Unload/Stop Pressure. What is Start/ Load Pressure? This is a pressure that is not normally reached unless an additional compressor needs to be started or loaded. This limit would be lower than the Target Pressure and the Unload/Stop Pressure. How is it used? The system pressure must be below this level before a start or load command will be sent. What is Unload/Stop Pressure? The upper limit of normal operating pressure fluctuation. This limit would normally be the same or slightly lower than the Target Pressure. This may, at first, seem incorrect because typically a compressor is unloaded if pressure is higher than necessary. However, a properly tuned controller will throttle the compressor or open the bypass valve to keep pressure near Target Pressure. The goal is to unload compressors that are not needed. The Unload Test (refer to section 5.6.5) will prevent a compressor from unloading if it is needed. How is it used? The average system pressure must be above this level before an unload or stop command will be sent. (To conduct the Unload Test, pressure must be above this level.) Adding these pressure limits to our first system pressure graph results in the following: Rev. 03 Date of Issue: 6/12/07 29

30 Figure 5-3: Pressure Limits Rev. 03 Date of Issue: 6/12/07

31 5.6.2 Time Limits Ingersoll Rand Self Control User's Manual Not only must Pressure Limits be considered. Time Limits are another factor. A fluctuation in system pressure is the result of some event that has taken or is in the process of taking place. Examples of events are: Compressor start or stop Workers taking breaks Shift changes Air demand increase or decrease If the event is of short duration, it might be unnecessary to respond to an increase or decease in pressure. If the recovery of a drop in pressure were imminent it would not be necessary to start or load another compressor. Assume the pressure to load or start the next compressor was 94 psi. If the event bottomed out at 93.5 psi and started to recover, the load or start command would not be necessary. See the next graph for illustration. Figure 5-4: Example of Acceptable Pressure Fluctuations Therefore, timers add a delay to the automatic functions for the purpose energy conservation. The timers that perform this function are Load Delay, Start Delay, Unload Delay, and Stop Delay. We will also cover the Wait Timer. Load Delay What is the Load Delay? This is a delay before sending a Load command to an unloaded compressor. How is it used? The system pressure must be below the Start/ Load Pressure for the duration of this timer before the Load command can be sent Rev. 03 Date of Issue: 6/12/07 31

32 Start Delay What is the Start Delay? This is a delay before sending a Start command and a Load command to a compressor that is Ready. Starting includes loading so that additional delay will not be added. How is it used? The system pressure must be below the Start/ Load Pressure for the duration of this timer before the start and load commands can be sent. Unload Delay What is the Unload Delay? This is a delay before starting an Unload Test and trying to unload a compressor. How is it used? The system pressure must be above the Unload/Stop Pressure for the duration of this timer before an Unload Test will begin. (Unload Test will be discussed later) Total Bypass myst be greater than or equal to the Allowed Bypass setting. Stop Delay What is the Stop Delay? This is a delay before sending a Stop command to an unloaded compressor. How is it used? The system pressure must be above the Unload/Stop Pressure for the duration of this timer before a stop command can be sent. Wait Timer What is the Wait Timer? This is a delay before any additional control functions may be evaluated. It allows the system to recover or respond to what has been done to it. How is it used? This delay is used after a start, stop, load, unload, unload test pass, or unload test fail Rev. 03 Date of Issue: 6/12/07

33 5.6.3 Automatic Loading One of the basic rules listed earlier says that If a compressor is running unloaded, that compressor will be loaded before another is started. This basically answers the question of which compressor to load next. The requirements of when to automatically load are: There is a compressor running Unloaded Pressure falls below the Start/ Load Pressure The Load Delay starts Figure 5-5: Unacceptable Pressure Drop If the Load Delay finishes and the pressure is still low then the compressor is commanded to load. Figure 5-6: Compressor Loads The Wait Timer now allows the system to recover or respond to what has been done to it Rev. 03 Date of Issue: 6/12/07 33

34 5.6.4 Automatic Starting One of the basic rules listed earlier says that A compressor is a candidate for starting if it is in a ready state (Ready). This basically answers the question of which compressor to start next. The requirements of when to automatically start are: There is not a compressor running unloaded Pressure falls below the Start/ Load Pressure The Start Delay starts Figure 5-7: Unacceptable Pressure Drop If the Start Delay finishes and the pressure is still low, the compressor is commanded to start and load. Figure 5-8: Compressor Start The Wait Timer now allows the system to recover or respond to what has been done to it. System pressure could recover. If pressure is still low at the end of the Wait Timer the Start Delay starts timing again Rev. 03 Date of Issue: 6/12/07

35 5.6.5 Automatic Unloading One of the basic rules listed earlier says that A compressor is a candidate for unloading if it is running and in a loaded state (Minload, Maxload, Loaded, Full Load). This basically answers the question of which compressor to unload next. Before further discussion on Automatic Unloading, Allowed Bypass and Total Bypass must be defined. What is Allowed Bypass? A number that indicates that the total bypass in the system is great enough to allow unloading a compressor. How is it used? The Unload Test will not begin until the total bypass valve sum is greater than this value. What is Total Bypass? The sum of all member compressor bypass valves. How is it used? The system will not attempt to unload a compressor until Total Bypass is more than the Allowed Bypass setting. What is Unload Test Rate? The rate in psi/min that the unload test lowers the compressors setpoint. How is it used? During an unload test the compressors setpoint is lowered at this rate. This provides a smooth gradual change to the setpoint avoiding step changes that could disturb the air system. What is Unld Test BV Max? It is the bypass valve position at which the compressor is assumed to be no longer providing air to the system. How is it used? During an unload test if the compressor s bypass valve is open more than this amount, the unload test passes and the compressor is unloaded. Unload Test What is the Unload Test? The Unload Test tests to ensure that a compressor can be safely unloaded. The test forces the compressor out of the system to determine if it is needed or not. How does it work? It lowers the compressor s setpoint by the Unload Test Rate. It monitors the system pressure to see that it stays above the Unload Test Pressure. If the pressure falls below the Unload/Stop Pressure the test fails and the setpoint is restored Rev. 03 Date of Issue: 6/12/07 35

36 It monitors the compressors bypass valve position to see if it opens past Unld Test BV Max. If the bypass valve is open more than the Unld Test BV Max then the test passes and the setpoint is restored. The above is repeated periodically until the test passes or fails. As a compressor s set point is lowered the discharge pressure on that machine begins to fall as the bypass valve goes further open. If System Pressure remains above the Unload/Stop Pressure the test will continue. When the compressor determines that its check valve has closed or its bypass valve opens more than Unld Test BV Max, the compressor will unload. The Unload Test will continue once started until it either passes or fails. How does the Unload Test fail? The compressor s Target Pressure (or User_PSP) is lowered The compressor s bypass valve is slowly forced open The system pressure is affected by the increased bypass (decrease discharge pressure) The other compressors in the system respond to the dropping system pressure by opening their inlet valves. The other compressors in the system cannot maintain system pressure. The system pressure falls farther each time the setpoint is lowered The system pressure falls below the Unload/Stop Pressure. The compressor s Target Pressure is set back to its normal value. (See following graph) Figure 5-9: Unload Test Fails Rev. 03 Date of Issue: 6/12/07

37 The above graph shows that if the Unload Test were not conducted the system pressure would remain acceptable but the one or more compressors would by bypassing (see light gray) How does the Unload Test pass? The compressor s Target Pressure (or User_PSP) is lowered The compressor s bypass valve is slowly forced open The system pressure is affected by the increased bypass (decrease discharge pressure) The other compressors in the system respond to the dropping system pressure by opening their inlet valves to correct system pressure The compressor determines that its check valve is closed, or its bypass valve opens farther than Unld Test BV Max The system pressure remains O.K. for the duration of the test The compressor is unloaded The compressor s Target Pressure is set back to its normal value. Figure 5-10: Unload Test Passes The above graph shows that system pressure is unaffected by unloading a compressor. (see light gray) Rev. 03 Date of Issue: 6/12/07 37

38 5.6.6 Automatic Stopping One of the basic rules listed earlier says, A compressor is a candidate for loading or stopping if it is running and in the unloaded state (Unloaded, or Autodual Unloaded). This basically answers the question of which compressor to unload next. The requirements of when to automatically stop are: There is a compressor running unloaded Pressure rises above the Unload/Stop Pressure The Stop Delay starts If the Stop Delay finishes and the pressure is still high then the compressor is commanded to stop. Figure 5-11: Compressor Stops Rev. 03 Date of Issue: 6/12/07

39 5.7 LOADSHARING OF CENTRIFUGAL COMPRESSORS Definition: A method of making air compressors in a system share the load more equally. Load sharing utilizes the maximum available throttle of each compressor to minimize costly air bypass to atmosphere, and automatically takes unnecessary air compressors out of the air system. This principle is illustrated below. Figure 5-12: Example of Operation Without Loadsharing Assume a system has three centrifugal compressors. This typical behavior of the compressors in a system with no load sharing is shown above. Note that Compressor #1 is fully loaded with its bypass valve closed. Note also that Compressor #2 is loaded and its bypass valve is closed. Compressor #3, on the other hand, is at its minimum load inlet valve position and its bypass valve is 100% open. This system could enjoy the benefits of Load Sharing: Reduce waste air More efficient operation of system Save money To eliminate the above waste, a system is needed to make the air compressors share the load more equally Rev. 03 Date of Issue: 6/12/07 39

40 5.7.1 Anti-Blowoff One way Load Sharing forces the compressors to share the load is through Anti- Blowoff. Before getting into how it works, a word should be said about Anti Bypass Gain. Anti Bypass Gain is defined as the ratio of a change in the output (of internal pressure setpoint) to a change in the variable (bypass valve position). If the Target Pressure is 125 psig and gain is 6, when the bypass valve is open 20% the internal pressure setpoint will be reset to psi. Internal SP = (Bypass Vlv % Open / 100 Anti Bypass Gain) + Target Pressure Anti-Blowoff works as follows: Each Peer-to-Peer member that is running loaded sets its Anti Bypass Gain every 20 seconds. (The value will expire after 30 seconds if no new gain is received) Anti-Blowoff will only have a direct effect on compressors that are bypassing The internal (not visible) pressure setpoint of these compressors is raised This leads to less bypassing, and an increasing system pressure This causes the compressors that are full loaded or modulating to reduce their output (to their inlet valves). This reduces the system pressure back to near the normal User_PSP value If a compressor is unloaded or is taken out of the Peer-to-Peer system it will return to its own local control. The next graph illustrates the three earlier compressors but now with load sharing. Figure 5-13: Anti-Blowoff Rev. 03 Date of Issue: 6/12/07

41 As a result of Anti-Blowoff Load Sharing the following benefits will be realized: The amount of bypassed air will be reduced, or eliminated The situation of one or more compressors operating at full load while the others are at minimum load will be eliminated No compressors are at full load No compressors are at 100% blowoff All compressors are dynamically controlling the system Total power is reduced for a given air demand Total waste (blowoff) is reduced Inlet Valve Load-Sharing Inlet Valve Load-Sharing encourages compressors in the system to distribute the load more evenly. Inlet Valve Load-Sharing is active only when no controlled compressor is at Minload. The operation is as follows: The control system sends the IV Load-Sharing Gain to the local controller of all compressors running at Minload every 20 seconds The internal (not visible) pressure setpoint of these compressors is raised. This causes the compressors that are full loaded or modulating to increase their output by opening inlet valves. This may result in a temporary increase of system pressure The equation for the internal pressure set point change is: Internal SP = (100 -Inlet Vlv % Open / 100 IV Load-Sharing Gain) + Target Pressure For example, take the case where Target Pressure is 125 psig, gain is 2 psi, and bypass valve is closed, and the inlet valve is 40%. The internal pressure setpoint will be reset to psi. If all other parameters remain constant, the local controller will need a higher volume output to increase the pressure 1.2 psi. It will increase the output by opening the inlet valve. The IV Load-Sharing Gain that is received by the local controller expires after thirty seconds. If a new value is not received within thirty seconds then the pressure set point of the controller will revert to Target Pressure Rev. 03 Date of Issue: 6/12/07 41

42 Figure 5-14: Inlet Valve Loadsharing Rev. 03 Date of Issue: 6/12/07