Marathon Computer AACC 2000 Adjusting the minimum on-time ‘mp.t’, Inertia and backlash settings

Page 60

Marathon Monitors Inc.

COMMISSIONING THE MOTORISED VALVE CONTROLLER

The commissioning procedure is the same for both bounded and boundless control modes, except in bounded mode you must first calibrate the position feedback potentiometer, as described in the section below.

Proceed as follows:

1.Measure the time taken for the valve to be raised from its fully closed to its fully open position and enter this as the value in seconds into the ‘tm’ parameter.

2.Set all the other parameters to the default values shown in Table 4-3.

The controller can then be tuned using any of the automatic, or manual, tuning procedures described earlier in this chapter. As before, the tuning process, either automatic or manual, involves setting the values of the parameters in Table 4-1. The only difference with boundless control is that the derivative term ‘td’, although present, will have no effect.

Adjusting the minimum on-time ‘mp.t’

The default value of 0.2 seconds is satisfactory for most processes. If, however, after tuning the process, the valve activity is excessively high, with constant oscillation between raise and lower pulses, the minimum on-time can be increased.

The minimum on-time determines how accurately the valve can be positioned and therefore the control accuracy. The shorter the time, the more precise the control. However, if the time is set too short, process noise will cause an excessively busy valve.

Inertia and backlash settings

The default values are satisfactory for most processes, i.e. ‘OFF’.

Inertia is the time taken for the valve to stop after the output pulse is turned off. If this causes a control problem, the inertia time needs to be determined and then entered into the parameter, ‘In.t’. The inertia time is subtracted from the raise and lower output pulse times, so that the valve moves the correct distance for each pulse.

Backlash is the output pulse time required to reverse the direction of the valve, i.e. the time taken to overcome the mechanical backlash of the linkages. If the backlash is

sufficient to cause a control problem, then the backlash time needs to be determined and then entered into the parameter, ‘bac.t’.

The above two values are not part of the automatic tuning procedure and must be entered manually.

CALIBRATING THE POSITION FEEDBACK POTENTIOMETER

Before proceeding with the feedback potentiometer calibration, you should ensure, in configuration level, that module position 2 (2a), or 3 (3a), has its ‘id’ indicating ‘Pot.i’, (meaning Potentiometer Input). Continue to scroll down the module

AACC 2000 Carbon

60

Nov. 1, 1997

Page 59 Page 61
Image 60
Page 59 Page 61
Contents Copyright Marathon Monitors INC Marathon Monitors Inc Mechanical Installation Safety Electrostatic discharge precautionsCleaning Electromagnetic compatibilitySafety Symbols WiringPower Isolation PersonnelOver-temperature protection Overcurrent protectionVoltage rating Conductive pollutionInstallation requirements for EMC Grounding of the temperature sensor shieldRouting of wires Environmental ratings Equipment ratingsElectrical safety GeneralMarathon Monitors Inc Installation Outline dimensions Model Outline dimensions Model 2000 controllerTo install the controller IntroductionController labels Unplugging and plugging-in the controllerRear terminal layouts Model Aacc 2000 rear terminal layoutMarathon Monitors Inc Sensor input connections Module 1, 2Two terminal modules SnubbersFour terminal modules COMDual output modules Connections for Process Value 3 in module position Connections for Process Value 2 PV2Communication module Wiring of 2-wire EIA-485 serial communications link EIA-485 wiringMarathon Monitors Inc Operation 26.0 Front Panel LAYOUTsButton or Name Explanation OP1OP2 SP2Alarms Basic operationOperating modes Automatic mode Output power demandHome display Display unitsManual Mode SetpointParameters and HOW to Access Them List header displaysMarathon Monitors Inc Parameter names Parameter displaysTo change the value of a parameter List 1OFFOFF PID PID.1Fact STDPass Name Description Prob Probe list Process Factor Millivolt input OffsetHydrogen or CO constant Name Description TunE DrADrA.t AdcPid PID list SEtRES HcbSetpoint list Input listOutput list CmS Comms listInFo Information list Access List FF.OPAlarms Diagnostic alarms Display What it means What to do about it Shows2b Diagnostic alarms Access Levels Access list header Password entryAccess to Read-only Configuration Configuration password Configuration levelLevel selection Setting operator access to a parameter Edit levelReturning to Operator Level Hiding or revealing a complete listPromoting a parameter This sheet intentionally left blank Tuning Parameter Code Meaning or FunctionOne-shot Tuning How to tuneTypical automatic tuning cycle Calculation of the cutback valuesAdaptive tune Manual Tuning Setting the cutback values Proceed as followsIntegral action and manual reset Automatic droop compensation AdcName Description Values Mtr Motor list Min Max Default Motorized valve controlAdjusting the minimum on-time ‘mp.t’ Inertia and backlash settingsMarathon Monitors Inc Enable in configuration level Gain schedulingSet the transfer point Configuration Selecting configuration level Press to enter configurationLeaving Configuration Level Changing the passwordsREU LIND1SA Enab SB.OPRely CMSNone DIG YESPMV InSt Instrument configuration Name Description Values MeaningH2O SP.FFProcess value config Input configurationCJC Setpoint configuration VAL.LVAL.H Alarm configuration Values Table a Alarm types ValueAlarm Modes Digital input 1 configuration Action on contact closure Digital input 2 configuration Action on contact closureIMP Alarm relay configuration VfltPflt Comms 1 module config Combining several digital events on to one outputModule config 1A b C1 Module 1 configurationCool 2A/b/C Module 2 configuration For ‘id’ = ‘LoG.i’ i.e logic input use the LA Conf’ list onDisplayed value low 3A/b/C Module 3 configuration SELC Module configuration Module configurationPoint Custom Linearisation VAL.1VAL.8 CAL Password configuration Exit Exit configurationDC Output Calibration User calibrationUser calibration User Calibration Enable Calibration Configuration ListUser Calibration Enable Exit configurationOffset calibration Input list headerCalibration type See table on the right for additional parameters Set OffsetTwo-point calibration Displayed ValueAdjust low-point calibration Select Low-point CalibrationAdjust High-point Calibration Select High-point CalibrationCalibration points and Calibration offsets Name Parameter description MeaningParameter Table Default HY1 Ssel FLT3 Marathon Monitors Inc AL1 Module 2A High Value VAL.1 101 Index Two-point calibration User calibration Aacc 2000 Carbon
Top Page Image Contents