Transcription of DULCOMETER Measurement and control systems
1 ProMinent DULCOMETER 1 DULCOMETER Measurement and control systemsAn Introduction to ProcessMeasurement and ControlProcess control in water treatmentinvolves Measurement of a variablerelated to water quality, combinedwith automation of chemical feedequipment or other physical/chemical processes to keep themeasured value as close aspossible to the desired setpoint orbetween high and low control 's approach combines thefunctions of an analyzer and acontroller into one instrument,dedicated to a specific water qualityparameter to simplify calibration ProMinent DULCOTEST sensor measures a specific waterquality parameter and sends anelectronic signal back to aDULCOMETER controller. Theoperator calibrates that sensor to aknown standard. It then displaysany changes that are measured inthat parameter within the sensor' Value OutputsUp to two outputs are controllers offerthe ability to continuously recordmeasured values to documentwater quality or to send to anothercontrol device.
2 Analog 4-20 mA or0-20 mA measured value outputsare proportional to the measuringrange of the sensor or spannable toprovide greater detail within asmaller range, for connection to achart recorder, datalogger ordistributed control system [D1C/D2C controllers andDULCOMETER transmitters(monitor only)] control OutputsDifferent control outputs areavailable to control virtually anytype of actuating relays change state (openor close contact) when the mea-sured value drops below or exceedsthe setpoint to start a processcontrol device or alarm, and shut itoff when the setpoint is reached(D1C or D2C).Analog control outputs (4-20 or 0-20mA) can drive a variable speedanalog control device, such as a DCSCR drive or AC inverter, accordingto the control action used (D1C orD2C).Pulse outputs are brief contactclosures to pace pulse-inputmetering pumps corresponding tothe control action used (D1C).Modulating relay outputs cause arelay to open and close accordingto the control action are used with solenoidvalves or constant-speed motor-driven metering pumps.
3 Minimumon-times may be set to preventoverheating of motors (D1C orD2C).3P relays provide two relay outputsto control a bi-directional actuator(such as a stroke length controlleron a metering pump) with provisionfor feedback potentiometer from theactuator to display the positionaccording to the control action used(D1C or D2C). control ActionsA variety of control actionsare available to suit theapplication and budget. Anyvariable control output listedabove may be used with anyof the control actions ControlSetpoint control uses asetpoint relay to start aconstant output pump oropen a solenoid valve whenthe measured value dropsbelow (or exceeds) thesetpoint. Once the mea-sured value reaches setpointagain, the pump stops or thevalve closes. This alwaysresults in overshooting thesetpoint because of the lagtime between the point ofchemical addition and thepoint of Measurement . Thiscan waste chemicals andcause excessive variation oneither side of the setpoint. Itis suited only for closedsystems or batch applica-tions where tight control isnot required (D1C or D2C).
4 Proportional ControlProportional control gives anoutput that is directlyproportional to the measuredvalue's deviation from thesetpoint. The farther fromsetpoint, the greater theoutput of the actuatingdevice, and the closer tosetpoint, the lesser theCONTROL ACTION RESPONSE INONCE-THROUGH SYSTEMSNote: Actuating device output increases measuredvalue in example ( chlorine feed) Measured value (as percent of Measurement range) Actuating device output (as percent)ProMinent DULCOMETER 2 DULCOMETER Measurement and control systemsoutput. Proportional control issuitable for closed systems or batchapplications where more precisecontrol is required. The propor-tional bandwidth may be spanned toset the distance from setpoint atwhich the actuating device isoperating at maximum output. Asmall bandwidth results in maxi-mum output at a measured valueclose to setpoint, and may causeovershooting. A large bandwidthmay result in long time periodsrequired until the setpoint isreached (D1C or D2C).
5 PID ControlPID control combines proportional,integral and derivative controlactions, or any combination control considers the timeinterval of deviation and increasesoutput when the deviation exceedsa programmed time control considers the rateof change of deviation and in-creases the output when the rate ofdeviation exceeds a programmedrate. PID control ensures the leastdeviation from setpoint possible(D1C, D2C). control TechniquesThe control technique useddepends on the location of thesensor in relation to the actuatingdevice, the presence of other inputswhich may effect the measuredvalue, or the requirement forsecondary actuating devices tohandle large swings. Somecommon control techniques aredescribed loop control is where thesensor is located downstream of theactuating device and measureschanges caused by the device. Thecontroller varies the device's outputto maintain the desired is usually used in recirculatingor batch applications, or once-through systems with constant flowrate.
6 The sensor must be locatedfar enough downstream to ensurethat any physical/chemical changesare complete, whether measuringpH, oxidant residuals or othervariables (D1C or D2C).Compound loop control combinesthe closed loop signal from thesensor with a second (disturbance)input, normally water flow rate, andchanges the actuating device'soutput in response to both vari-ables. This is typically used inonce-through applications withvarying flow rates (D1C).Base and trim control uses twoactuating devices to bring largefluctuations into control very quickly,yet provide tight control undernormal operation. A variable outputactuating device is normally usedwith proportional or PID control forthe trim or fine tuning. A constantoutput device would be started by asetpoint relay for the base load tomake fast changes in the event oflarge fluctuations that the trimdevice cannot handle (D1C orD2C).Bi-directional control of two oppos-ing actuating devices, such aspumps for acid and base in a pHcontrol application, is possible withone controller (D1C or D2C).
7 Toprevent repeated correctionscaused by overshooting on bothsides, a deadband may be pro-grammed (between two setpoints)in which both actuating devices arestopped (D1C or D2C).With open loop control , the sensoris upstream of the actuating deviceand a control signal changes theactuating device's output. Usually,this is only used when the resultingmeasured value would be outside ofthe sensor's measuring range (D1 Cor D2C).CLOSED LOOPCOMPOUND LOOPOPEN LOOPBASE AND TRIMBI-DIRECTIONALCONTROL (D2C) Acid ChlorinePROPORTIONAL control ONLY (BATCH LINE)ProMinent DULCOMETER 3 DULCOMETER Measurement and control systemsSystem ComponentsThe ProMinent catalog lists avariety of components that must becombined to create a functionalcontrol system . Please ensure thatyou select all required components,as follows:Minimum Requirements Controller Sensor(s) Sensor holder(s) (to mountsensor in process) Sensor cable(s) (to connectsensor to controller) Standardizing solution(s) (for pHor ORP, others use the samplewater analyzed on site forcalibration) Metering pump(s) with controlinput matched to controller'soutputOptional Equipment1.
8 Impedance converter (millivolt) tominimize interference andmaximize sensor life whendistances between pH, ORP ortemperature sensors and thecontroller are between 30 and300 feet. Provides lowimpedence mV 4-20 mA Signal Converters forpH, ORP or temperature sensorswhen distances between thesensor and controller is up to 300feet, or where required by thecontroller ( pH correction forchlorine). Provides 4-20 Chart recorder4. Spare membrane caps andelectrolyte for membrane 2-wire shielded cable fortransmission of 4-20 mA in-line sensor housings, DULCOTEST instrumentation andDULCOMETER D1C panel/wall mount controllersWhat do I need to order with a D1C?ChlorinepHORPD1C ControllerD1C controllerD1C controllerPower cordPower cordPower cordChlorine sensorpH sensorORP sensor25 mm mm mm DGMA2-wire cablepH buffersORP standardMounting set for sensor2xSN6 cable or2xSN6 cable or pH transducer/ 2-wire cable pH transducer/ 2-wire cableOptional (free Chlorine)Opt. (temperature comp.)
9 Opt. (temperature comp.)pH sensor for comp. (free)temp. sensor for sensor for transducer/2-wire cableSN6 cable w/ extension wireSN6 cable w/ extension mm DGMATemp. transducer if long cableTemp. transducer if long cablepH buffers2-wire cable for transducer2-wire cable for transducerextra 2-wire cableextra 2-wire cableextra 2-wire mm mm DGMAWhat do I need to order with a D2C?pH/ ChlorinepH/ ORPpH/ pHD2C ControllerD2C controllerD2C controllerPower cordPower cordPower cordpH sensorpH sensor2xpH sensorsChlorine sensorORP sensorpH transducer2-wire cableORP transducer2xSN6 connector or2xSN6 connector or2-wire cable pH transducer/ 2-wire cable pH transducer/ 2-wire cable2xSN6 connector orpH bufferspH buffers pH transducer/ 2-wire mm DGMAs25 mm DGMApH buffers2-wire cableMounting set for sensorORP mm mm DGMAsOptionalOptionalOptionalextra 2-wire cableextra 2-wire cableextra 2-wire cableTemp. sensor for pH temp. comp. Temp. sensor for pH temp. comp. Temp. sensor for pH temp.
10 Mm mm mm DGMASN6 cable w/ extension wireSN6 cable w/ extension wireSN6 cable w/ extension wireTemp. transducer if long cableTemp. transducer if long cableTemp. transducer if long cable2-wire cable for transducer2-wire cable for transducer2-wire cable for transducerProMinent DULCOMETER 4 DULCOMETER D1C and D2C Series Process Controller Single Variable Controllers (D1C) and Dual Variable Controllers (D2C) for Water and Wastewater Treatment or Industrial Process ControlThe D1C/D2C integrates process monitoring and control into a single, easy-to-use device, replacing separateand multiple monitors and controllers: ProMinent DULCOTEST sensors measure the process; and the controllerdisplays the value on a large LCD screen; control outputs can operate various control devices ( meteringpumps) to keep the process within control limits using proportional or PID control action; alarm relays areavailable for fault annunciation and analog outputs are available for recording the measured value.
