Emerson 20/20 service manual Variable Frequency Drive VFD, VFD One-Step Control Method

Page 41

Section 6 • Compressor Control

The auto-cycle function will operate only in local “Auto” mode and Direct I/O “Remote Auto” mode. If the au- to-cycle feature is enabled while running in any other remote mode, the function will simply be ignored. However, the Minimum slide position will continue to be respected in Remote “Auto” mode. If the compres- sor changes from a remote mode back to Local “Auto” mode, the auto-cycle feature will operate normally.

NOTE

When the Pump-down Feature is enabled, the Auto- cycle setpoints are automatically disabled. Pump- down mode will cause the compressor to cycle off via the Pump-down Stop Pressure setpoint, and will not allow the compressor to start again.

Enable:

•Enables the Auto-cycle control. Uncheck the box to disable the Auto-cycle set-points.

Start Pressure:

•When the suction pressure meets or exceeds this set- point, the compressor will start.

Start Delay:

•Delays the compressor from starting when the suc- tion pressure meets or exceeds this setpoint.

Stop Pressure:

•When the suction pressure meets or falls below this setpoint, the compressor will stop.

Stop Delay:

•Delays the compressor from stopping when the suc- tion pressure meets or exceeds this setpoint.

Minimum Slide Position:

•The minimum capacity slide position that the com- pressor is allowed to run at.

Variable Frequency Drive (VFD)

The VFD page is where the operator can tune the mo- tor VFD for desired operation. A Vilter compressor uses the variable speed of a VFD controlled motor to vary the amount of work or capacity of the compressor. The basic one step VFD control will use the capacity slide to control the first half of the total available capacity and the motor speed to control the second half of the total available capacity, see Figure 6-3. VFD One-Step Control Method. For example, if the compressor needs to load to 100% of its capacity. The control algorithm will first move the capacity slide to its maximum position, then the motor speed will ramp up to its maximum speed. In the unloading direction, the motor speed will ramp down to its minimum speed, then the capacity slide will move to its minimum position.

The two-step control method works much like the one- step method but divides the control into four sections, see Figure 6-4. VFD Two-Step Control Method. While loading; the compressor will first move the capacity slide to the maximum set for step one then speed up the motor to its maximum speed for the same step. Once step one has completed, the control algorithm will again move the capacity slide to the maximum position and the maximum speed of step two. At this point the com- pressor would be fully loaded. Unloading occurs in the reverse direction. The two-step control method is not typical for most installations and is normally used when a Vilter engineer recommends it.

Figure 6-3. VFD One-Step Control Method

Figure 6-4. VFD Two-Step Control Method

Vission 20/20 • Operation and Service Manual •Vilter/Emerson • 35391SC 1.8.5153

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Contents Vission 20/20 micro-controller Page Table of Contents Digital I/O Board Layout Top Status Bar TOCCompressor Sequencing Event List Data Backup List of Tables and Figures END of TOC How to Use This Manual Requirements to Start Compressor Operational Flow ChartsCritical Compressor Run Logic at Compressor Start Compressor Amperage Load LimitingOperational Flow Charts 2 Voltage Source Installation RecommendationsProper Wiring Sizing Mixing Voltages DC signalsGrounding Correct Transformer Wiring Method Wiring MethodsBest Practices Overview Hardware ArchitectureDigital Input/Output I/O Board Description Type Digital I/O 1Refer to -2. Analog Inputs Motor Current Analog InputsAnalog Inputs 1 Digital I/O 2Digital & Analog I/O Boards Layout Analog OutputsDigital I/O Board Layout Analog Inputs 2Digital Output Board Layout Digital Output BoardsDigital Input Board Layout Digital Input BoardsDigital Input-Output Board Layout Digital In-Out BoardsAnalog Input Board Layout Analog Input BoardsAnalog Input Jumper Tables Channel SignalJP-13 JP-14 JP-15 JP-31 Analog Output Board Layout Analog Output BoardsMain Screen Main ScreenTop Status Bar Parameter Bar Unit Start Pop-Up Window Bottom Status Bar Splash Screen Navigation Buttons Menu ScreenMenu Screen Pulse Proportional Control Compressor ControlProportional Band & Setpoint Auto-CycleVFD One-Step Control Method Variable Frequency Drive VFDPumpdown Control Pulldown Control Volume Slide Position Offset Control ModeStop Load and Force Unload Capacity Slide Triggered OutputsLiquid Injection Load AnticipatingOil Control Compressor Control Alarms and Trips Setpoints Alarms and TripsAlarms and Trips Compressor Inhibits Safety Failure MessagesFalse Start Timer Setpoints TimersOil Separator Level #2 Safety Trip Delay Timers Blank Scheduling Setpoint Compressor SchedulingCompressor Scheduling Pressure Control Setpoints Compressor SequencingCFM Equipment List 10 4 / Blank Condenser Control Setpoint Condenser ControlStep Control Step Control Screen VFD Settings11 4 / Blank Digital Outputs Service OptionsAnalog Outputs Instruments Calibration Pressure and Temperature InputsRemote Capacity Motor CurrentAnalog Inputs 13 4 / Blank Capacity Slide Valve Potentiometer Slide CalibrationSlide Valve Actuator Calibration for Optical Style Motors Volume Slide Valve PotentiometerSlide Valve Operation Photochopper Command Shaft Rotation Required By Actuator Command Shaft RotationSlide Valve Troubleshooting Guide 1 Slide Valve Troubleshooting GuideSlide Valve Troubleshooting Guide 2 LED Blink Codes and Troubleshooting Guide 1 Slide Valve Actuator Troubleshooting Guide Blink CodePleted. The actuator will not move while this error code LED Blink Codes and Troubleshooting Guide 2Chart Operation Trend ChartTrend Data Storage Trend Setup Screen Setup15 4 / Blank Event list Columns Event List16 2 / Blank Input/Output Screen Input / Output17 2 / Blank Digital Inputs Auxiliary Input / OutputDigital Outputs Control 18 4 / Blank Time & Date ConfigurationUnits Anti-Recycle CommunicationsTouchscreen Compressor Sequencing Restart On Power FailureLanguage Model & RefrigerantOptional Function Selection Compressor ControlOil Pump Condenser ControlOil Cooling Motor Current DeviceDigital Inputs Analog Inputs Analog Outputs Configuration 19 10 / Blank Save / Load Data BackupData Backup Migrate Factory Reset20 4 / Blank Checklist MaintenanceLog ChartApply User AccessManage Accounts LoginScreen Security Levels Security Access Levels22 4 / Blank Help Screen Screen FeaturesVersion Pop-Up Screen Twin Screw Control Screen Twin Screw ControlOperation Cool Compression Control Screen Cool Compression ControlCool Compression Control Functions Screen Control FunctionsOperational Differences from Single Screw Auto Load TimerCool Compression Control

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