Better PID Control with FF than 4- 20 mA 1 1 Successful - - PowerPoint PPT Presentation

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Jan 27, 2023 328 likes •458 views

Better PID Control with FF than 4- 20 mA 1 1 Successful Implementation & Improved Operation Video A study made by Industrial Systems and Control (ISC) in Glasgow A spin-off company from University of Strathclyde

SLIDE 1

1 1

Successful Implementation & Improved Operation

Better PID Control with FF than 4- 20 mA

SLIDE 2

2 2

Successful Implementation & Improved Operation

Video

 A study made by Industrial Systems and Control

(ISC) in Glasgow

 A spin-off company from University of Strathclyde

http://www.controleng.com/media-library/videos/videos/video-understanding-the-user-case-for-cif.html

SLIDE 3

3 3

Successful Implementation & Improved Operation

Summary

 For fast loops the performance of fieldbus control

in the field is significantly better than 4-20 mA

 Benefits of the very highly deterministic nature of

control in the field really come into its own on fast process control loops:

– Pressure – Flow

 For pressure and flow loops the performance

improved by 10-15% over a 4-20 mA loop

SLIDE 4

4 4

Successful Implementation & Improved Operation

Summary (Cont’d)

 For slow loop (50 second or a 1 minute) the

performance benefit is less

SLIDE 5

5 5

Successful Implementation & Improved Operation

Test Results (250 ms process time)

 No performance difference between fieldbus and

4-20 mA loops for P and PD controllers

 For PI and PID fieldbus (CIF) performs better

than 4-20 mA

– 14.8% better for regular stepping disturbance – 29.3% better for stochastic disturbance – If the disturbance is varying slowly the improvement is less significant

SLIDE 6

6 6

Successful Implementation & Improved Operation

Test Results (10 second process time)

 Negligible performance difference between

fieldbus and 4-20 mA loops for P and PD controllers – for slow disturbances

 Fieldbus improvement for PI and PID

– (Most beneficial at slow controller cycle time; significant if controller is run slow to decrease load; more loops per controller)

Controller Scan Time Step Disturbance Stochastic Disturbance 250 ms 6% 5.5% 500 ms 1% 8.5% 1000 ms 8% 15%

SLIDE 7

7 7

Successful Implementation & Improved Operation

Test Results (50 second process time)

 Fieldbus improvement for PI and PID

– (Most beneficial at slow controller cycle time; significant if controller is run slow to decrease load; more loops per controller)

Controller Scan Time Step Disturbance Stochastic Disturbance 250 ms 1.5% 1.5% 500 ms 2.4% 2.5% 1000 ms 4.4% 4.8%

SLIDE 8

8 8

Successful Implementation & Improved Operation

Disturbance Rejection

 Loops affected by fast disturbances benefit the

most

 Slowly varying disturbance like ambient

temperature sees no performance benefit

 There are a lot more benefits to using control in

the field than just the determinism

– This study just looking at the control loop performance

i.e. how much the process variability can be reduced by

fieldbus

SLIDE 9

9 9

Successful Implementation & Improved Operation

Significance of the ISC Study

SLIDE 10

10 10

Successful Implementation & Improved Operation

Why Does Fieldbus Control Better than Analog?

 CIF is „jitter‟ free (constant sampling time)

– Fieldbus devices are time synchronized – Fieldbus communication and control is scheduled – A 250 ms macrocycle is 250 ms every time

 4-20 mA control loops have jitter

– Because AI and AO cards are not time synchronized with the controller – AI and AO scan is independent of control – A 4-20 mA loops has:

Varying sampling time (not ideal for PID)
Longer total loop latency (input to output)

Control Control A I A I A I A I A I A I A I A I A I A I A I A I A I A I A I A I A I A I 4-20 mA Input Card Controller Jitter

SLIDE 11

11 11

Successful Implementation & Improved Operation

Why is High Process Variability Bad?

 High process variability causes alarms

– So operators shift the setpoint away from ideal to avoid these alarms (“comfort margin”)

This reduces efficiency:

– Lower throughput – Higher consumption of energy and other utilities

20 40 60 80 100 120 5 10 15 PV Setpoint Hi Alarm 20 40 60 80 100 120 5 10 15

High variability: causes alarms... ...so operators shift the setpoint

SLIDE 12

12 12

Successful Implementation & Improved Operation

Low Process Variability with Fieldbus

 Low process variability

– Setpoint can be set closer to ideal

This increases efficiency:

– Higher throughput – Lower consumption of energy and other utilities

– More uniform product: greater quality/yield

20 40 60 80 100 120 5 10 15 PV Setpoint Hi Alarm

High variability: causes alarms...

20 40 60 80 100 120 5 10 15

1 1

Better PID Control with FF than 4- 20 mA

2 2

Video

 A study made by Industrial Systems and Control

(ISC) in Glasgow

 A spin-off company from University of Strathclyde

3 3

Summary

 For fast loops the performance of fieldbus control

in the field is significantly better than 4-20 mA

 Benefits of the very highly deterministic nature of

control in the field really come into its own on fast process control loops:

– Pressure – Flow

 For pressure and flow loops the performance

improved by 10-15% over a 4-20 mA loop

4 4

Summary (Cont’d)

 For slow loop (50 second or a 1 minute) the

performance benefit is less

5 5

Test Results (250 ms process time)

 No performance difference between fieldbus and

4-20 mA loops for P and PD controllers

 For PI and PID fieldbus (CIF) performs better

than 4-20 mA

– 14.8% better for regular stepping disturbance – 29.3% better for stochastic disturbance – If the disturbance is varying slowly the improvement is less significant

6 6

Test Results (10 second process time)

 Negligible performance difference between

fieldbus and 4-20 mA loops for P and PD controllers – for slow disturbances

 Fieldbus improvement for PI and PID

– (Most beneficial at slow controller cycle time; significant if controller is run slow to decrease load; more loops per controller)

Controller Scan Time Step Disturbance Stochastic Disturbance 250 ms 6% 5.5% 500 ms 1% 8.5% 1000 ms 8% 15%

7 7

Test Results (50 second process time)

 Fieldbus improvement for PI and PID

– (Most beneficial at slow controller cycle time; significant if controller is run slow to decrease load; more loops per controller)

Controller Scan Time Step Disturbance Stochastic Disturbance 250 ms 1.5% 1.5% 500 ms 2.4% 2.5% 1000 ms 4.4% 4.8%

8 8

Disturbance Rejection

 Loops affected by fast disturbances benefit the

most

 Slowly varying disturbance like ambient

temperature sees no performance benefit

 There are a lot more benefits to using control in

the field than just the determinism

– This study just looking at the control loop performance

fieldbus

9 9

Significance of the ISC Study

10 10

Why Does Fieldbus Control Better than Analog?

 CIF is „jitter‟ free (constant sampling time)

– Fieldbus devices are time synchronized – Fieldbus communication and control is scheduled – A 250 ms macrocycle is 250 ms every time

 4-20 mA control loops have jitter

– Because AI and AO cards are not time synchronized with the controller – AI and AO scan is independent of control – A 4-20 mA loops has:

Control Control A I A I A I A I A I A I A I A I A I A I A I A I A I A I A I A I A I A I 4-20 mA Input Card Controller Jitter

11 11

Why is High Process Variability Bad?

 High process variability causes alarms

– So operators shift the setpoint away from ideal to avoid these alarms (“comfort margin”)

– Lower throughput – Higher consumption of energy and other utilities

High variability: causes alarms... ...so operators shift the setpoint

12 12

Low Process Variability with Fieldbus

 Low process variability

– Setpoint can be set closer to ideal

– Higher throughput – Lower consumption of energy and other utilities

– More uniform product: greater quality/yield

High variability: causes alarms...

Low variability: setpoint need not be changed