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Process Control What does this block diagram mean? PIDG(s) Controller Plant OP PV SP Error.

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Presentation on theme: "Process Control What does this block diagram mean? PIDG(s) Controller Plant OP PV SP Error."— Presentation transcript:

1 Process Control What does this block diagram mean? PIDG(s) Controller Plant OP PV SP Error

2 Control Terms - Three Term Control Proportional ---- Proportional Band Integral ---- Integral Time Constant Derivative ---- Derivative Time Constant Output ( OP ) = K ( 1 + xdt + dx/dt ) ( P I D) PIDG(s) Controller Plant OP PV Error SP

3 Loop Response Under Damped--Overshoot gives minimum time to setpoint Critically Damped--No overshoot and stable Over Damped--No overshoot but excessive time to setpoint Under Damped Over Damped Critically Damped Setpoint Time

4 Loop Tuning Setpoint t osc x x t Time Rule Of Thumb: Proportional Band--P = 2* Integral Time Constant--I = 1.5* Derivative Time Constant--D = I/5

5 Three Term Control How can I relate this loop response to my process? Under Damped Over Damped Critically Damped Setpoint Time

6 Proportional Term Analogy Speed (mph) Depress gas pedal Ease off gas pedal Proportional Band mph 40 mph46 mph Time

7 Integral Term Analogy Speed (mph) Slowly depress gas pedal to reach 50 mph mph48mph50mph Time

8 Derivative Term Analogy Speed (mph) Proportional Band mph 49 mph 50 mph 51 mph 50 mph Time

9 Process Control How many parameters are controlled in my Cast Film or Blown Film process? & How do they differ from each other in terms of speed of response?

10 Cast Film DD DDD D Th SMPBarrelDie G/B DDrive speed controlMPMelt pump TTemperature controlPPressure control SCScreen changerSScanning frame G/BGravimetrics / BlenderThThickness control SCSC T P

11 Blown Film D Barrel G/B SCSC Die Tr D D D S Th T DDrive speed control TTemperature control SCScreen changer G/BGravimetrics / Blender Th Thickness control SScanning frame ABAir board CCage BBubble diameter sensing Tr treater D C B B

12 Use Of Computer Systems What benefits can I achieve by using a computer system on my process? & How is my process control equipment connected to a computer system?

13 Computer Supervision - 1 A computer system provides: One window to view all line information The ability to modify line parameters Storage and download of stored recipes Live trending of data

14 Computer Supervision - 2 Additional computer system benefits are: Generation of batch and shift reports Statistical Process Control (SPC) trending and data Historical trend and data information Networking of data to other departments

15 Linking to the Computer - 1 Temperature Control Drive Control Thickness Gauge Gravimetric Blending Pressure Control PLC Control Industrial Computer Ideal Temperature Control Drive Control Thickness Gauge Gravimetric Blending Pressure Control PLC Control Industrial Computer Actual

16 Linking to the Computer - 2 Improved system Industrial Computer Temperature and Pressure Control Drive Control Gravimetric Blending Thickness Gauge PLC Control Temperature Control Pressure Control Gravimetrics / Blending PLC Drive Control Scanning Frame Industrial Computer OEM system

17 Digital Communications My computer has RS232 and the process equipment has RS232. This is all I need, right? Wrong!

18 RS (EIA) 232, 422 & 485 Analogy EIA-232: 3 - wire connection ( plus enable links ): Tx, Rx, Common Point to point ( one to one ) Short distance transmission ( <50ft / 15m ) EIA-422/485: 5-wire connection (422):Tx+, Tx-, Rx+, Rx-, Common 3-wire connection (485):A (Tx+ & Rx+), B (Tx- & Rx-), Common Multi drop capability: ( 8 for EIA 422 and 32 for EIA 485 ) Long distance transmission ( 4000ft / 1230m ) EIA-232 & EIA-422/485 are analogous to using the air as the transmission medium for us to communicate. They do not tell us how we communicate.

19 EIA-232 / EIA 422 (485) Explained TxRx Input signalRecovered signal Noise pulse EIA 232 TxRx _ Input signalRecovered signal Noise pulse Signals subtracted EIA 422 (485)

20 Communications Protocol Analogy ' Allo! Pronti! Hullo! Hola! Moshi moshi! Hello!


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