Tuning Control Loops

Tuning Control Loops

Scribd Upload a Document Search Books, Presentations, Business, Academics...

Explore

Documents Books - Fiction Books - Non-fiction Health & Medicine Brochures/Catalogs Government Docs How-To Guides/Manuals Magazines/Newspapers Recipes/Menus School Work + all categories Featured Recent

People Authors Students Researchers Publishers Government & Nonprofits Businesses Musicians Artists & Designers Teachers + all categories Most Followed Popular 1

Nurgul Shuakbayeva / 7

Account Search coming soon Home

My Documents My Collections My Shelf View Public Profile ad this Document DocuMessages ment for Free Free Notifications Settings Help Log Out


Tuning Control Loops Page 2 of 7 Assume 50% proportional band, PB = PROPORTIONAL BAND GAIN = 100% (span) 50% (PB)


GAIN = 2 Honeywell uses letter “K" to represent GAIN, therefore K = 2. INTEGRAL OR RESET (T1) •

Integral action repeats the proportional controllers initial corrective signal until there is no difference between the PV and Setpoint. •

Integral ( T1 ) is expressed in "Minutes per Repeat" DERIVATIVE(T2) •

Changes the output of a controller in proportion to the "RATE" or "SPEED" at which the controlled variable is moving towards or away from the setpoint. •

Derivative action is expressed in minutes. •

Represents the time that the proportional plus derivative will take to reach a certain level of output, in advance of the time proportional action alone would produce the same output. i.e: When derivative is applied to a two mode controller ( PI ), to make it a three mode controller ( PID ), it's action consists of decreasing the number of repeats per minute required to drive the error back to setpoint. TUNING ADJUST PROPORTIONAL BAND

Always tune proportional band with very little reset action. That is, for instance with a speed control loop, always set the reset (integral) adjustment at, say twenty or thirty seconds or more before adjusting the proportional band. Then, adjust the proportional band to a smaller value (higher gain) until cycling or instability begins. EXAMPLE: Start with 40% proportional band (a gain of 2.5); then halve the proportional band to 20% (a gain of 5); then halve the proportional band to 10% (a gain of 10); etc. When cycling just begins, increase the proportional band by 50 percent. That is, from 10% to 15%; from 18% to 24%; etc. Cycling should stop. The proportional band adjustment should now be properly set and should be left at this value. ADJUST RESET (INTEGRAL) ACTION

This is done by reducing the time value (in seconds). Say the reset is at twenty seconds. Then reduce the reset to ten seconds; then reduce the reset to five seconds; then reduce the reset to two seconds; etc. Tuning Control Loops When Page 3cycling of 7 or instability begins, increase the reset adjustment by 50%. Berry’s Commissioning Handbook

Example: If cycling is observed at two seconds, increase the reset to three seconds. If cycling is observed at 8 seconds, increase the reset to 12 seconds, etc. The reset action should now be properly adjusted and should be left at this value. ADJUST DERIVATIVE ACTION (RATE)

If a derivative adjustment is felt necessary, adjust the derivative action by beginning at a setting of one


second, then two, then three, until improvement is observed and seems to be optimal. Normally, derivative action is not needed and does not help the situation.

TUNING CONTROLLERS Since there are a very large number of combinations of the two or sometimes three, "knobs" provided for controller tuning, many methods have been developed over the years to aid in their proper adjustment. A few require upsetting the process to some extent, often an unacceptable practice in real life. These notes are intended to provide a few simple rules to use in tuning controllers which will minimize upsets and still get the job done. THE CONTROLLER MUST BE ADJUSTED TO BALANCE THE PROCESS.

If the process is fast to respond (i.e. a flow loop), then the controller must be tuned fast too. Fast or slow for a controller refers to integral (or reset). NOT PROPORTIONAL BAND (or gain). Do not confuse these actions or grief will be your constant companion during your controller tuning efforts. If the process is slow (i.e. temperature control of a tray part way up a distillation column), then the controller must be tuned slow TO MATCH THE PROCESS. If you do not have a feel for the process characteristics or cannot find someone to enlighten you, leave controller tuning to someone else who can get the needed information. GENERAL RULES FOR COMMON LOOPS FLOW

Usually, at least half of the control loops in a plant are flow loops. Set integral (I) at 0.1 minutes. Adjust the proportional band so that the measurement is not too noisy, usually about 300% although an occasional poor meter run installation may require as much as 1000%. A loop where a valve positioner has been used will require a proportional band setting two to Tuning Control Loops three times larger than for a loop without a positioner. Slow moving or sticky control valves Page 1 of 7 0.2 or 0.3 minutes but are rare exceptions. If these settings do not work, inspect may require Tuning the valve Control and orificeLoops installation to find the, problem. Fix the problem. Do not adjust the Table of Contents controller to some ridiculous setting such as a 10 minute reset time. Use the controller in manual or a hand valve if you think a 10 minute reset time is necessary. TUNING CONTROL LOOPS...................................................................................................1 TUNING CONSTANTS....................................................................................................1 IMPORTANT NOTE: No controller will work when the valve is almost closed or almost wide PROPORTIONAL BANDunder (K)......................................................................... . . . a. bypass . . . . . .(if . . one . .1 open. Don't attempt tuning these conditions. Have the operator open or close GAIN (K) CALCULATION..........................................................................................1 exists) or wait until process conditions change enough to get the valve back within its operating INTEGRAL RESET (T1)..........................................................................................2 range (from 5 or to 95% of travel as extreme limits with 10 to 90% as a safer range). Never use DERIVATIVE (T2).........................................................................................................2 derivative action in a flow loop. TUNING.............................................................................................................................2 ADJUST LEVEL PROPORTIONAL BAND........................................................................ . . . . . .2 Berry’s Commissioning Handbook ADJUST RESET (INTEGRAL) ACTION....................................................................2 ADJUST DERIVATIVE ACTION (RATE)...................................................................3 TUNING CONTROLLERS...................................................................................................3 GENERAL RULES FOR COMMON LOOPS..................................................................3 FLOW.............................................................................................................................3 LEVEL...........................................................................................................................3 LIQUID PRESSURE.....................................................................................................4 GAS PRESSURE........................................................................................ . . . . . . . . . . . . . . . . . . .4 TEMPERATURE, VAPOR PRESSURE, AND COMPOSITION.................................4


CLASSICAL CONTROLLER TUNING METHOD....................................................5 CASCADE AND OTHER INTERACTING CONTROL LOOPS................................5 DEFAULT CONTROLLER TUNING PARAMETERS....................................................6 CONTROL LOOP SCAN RATES.................................................................................6 PID ALGORITHM DEFAULT TUNING CONSTANTS..............................................6

TUNING CONTROL LOOPS TUNING CONSTANTS PROPORTIONAL BAND (K) •

If Proportional Band is 100%, each percent of change at the input to the controller will produce the same percent of change at the controller's output. •

If a Proportional Band is less than 100%, each percent change of input signal to the controller will produce a greater percent of change at the controller's output. •

If a Proportional Band is larger than 100%, each percent change in input signal to the controller will produce a smaller percent of change at the controller's output. •

The Proportional Band that is selected for a particular operating situation determines how much corrective signal the controller can produce for each percent of change in the variable controlled by the controller. •

The controller's output signal determines the amount of movement that will be produced at the control valve. GAIN (K) CALCULATION

Ratio of entire span of measurement to percent span being used as Proportional Band. GAIN = 100% (the entire span of measurement) % of span being used as a proportional band Berry’s Commissioning Handbook




Tuning Control Loops Download this Document for FreePrintMobileCollectionsReport Document This is a private document.

Info and Rating Flow sensors field instrument instrumentaion Dineshlp You like this.Unlike · Admin

Ads by Google

Time Mark Liquid Level Controls At Midwest Equipment Discount Pricing, Shop Online www.MidwestEquipment.com

Level & Flow Sensors Competitive Costs, Budget Friendly Reliable Products,Discounts & More! www.thomasprod.com

Flow and Level Sensors Liquid control, versatile solutions, low cost devices www.icos.com.br

Sign Up for an Ad- Free Scribd Remove all ads. Never see ads on Scribd again. No Thanks

Share & Embed Related Documents PreviousNext 1.

13 p. 13 p. 13 p.


2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

136 p. 136 p. 136 p. 32 p. 32 p. 73 p. 73 p. 73 p. 73 p. 73 p. 73 p. 73 p. 73 p. 12 p. 4 p. 73 p. 8 p. 1 p. 3 p. 1 p. 13 p. 1 p. 16 p. 1 p. 5 p. 56 p. 15 p. 2 p. 19 p.

More from this user PreviousNext 1.

2.

3.

4.

5.

357 p. 2 p. 1 p. 8 p. 32 p. 15 p. 1 p. 4 p. 4 p. 4 p. 8 p. 52 p. 18 p. 13 p. 20 p.


6.

14 p. 1 p. 28 p. 7 p. 6 p. 10 p. 2 p. 7 p. 11 p. 3 p.

7.

8.

9.

Recent Readcasters

Add a Comm ent

Submit 

Upload a Document

About Press Blog Partners Branded Reader Web Stuff


Scribd Store Support FAQ Developers / API Jobs Terms - General Copyright Follow Us! scribd.com/scribd twitter.com/scribd facebook.com/scribd

Tuning Control Loops

Recommend Documents