IRIS diaphragm control valve Regulation consequence

Mannheim(DE) London (GB) Milano (IT) Lyon (FR) S.Sebastian (ES) Bruxelles (BE) Graz (AT) Hilversum (NL) Stenungsund (SE)

Regulation consequence In this paragraph, we are going to express different states of regulation according to the oscillation expressed by the real value according to a W value of oxygen. According to the recorded variations, it is possible to draw some conclusions from the recorded faults/failures and analyse them in order to enhance the stability of the regulation.

BS-955-04gb

Dat. 01.01.2003

Regulation is all right The measured value remains in a required tolerance.

The quality of the regulation deteriorates over a period of time. Possible reasons: - difficulty operating of the valve or blockage - loose or worn valve mechanism - faulty positioner - regulating adjusted too slowly

Oscillation of regulation only at certain times of operation. - regulating to «re-parametered» - regulating valve with the bad BKL profile (outside stable control range) - mechanical or hydraulic fluctuations (hysteresis)

Dead measure: - bad scale or calibration - defective measuring probe - defective positioner

Emile Egger & Cie SA Cressier/NE (Suisse)

Hysteresis and its consequences

Mannheim(DE) London (GB) Milano (IT) Lyon (FR) S.Sebastian (ES) Bruxelles (BE) Graz (AT) Hilversum (NL) Stenungsund (SE)

Hydraulic hysteresis arises when hydraulic flow is disturbed. The hydraulic disturbances may be caused by breakaway edges or decentral, respectively irregular flow geometry. Mechanical hysteresis may be caused by too high static friction, floating in the mechanics or a generally unstable construction. The repeating accuracy of the control actuator can be important, too. The consequence are oscillations in the control loop – the valve is constantly adjusting. As all components of the control loop cannot work better than the valve, the quality of the whole system is reduced.

Example: hysteresis by deviation from kv value - no defined values can be aimed

0

5000

10000

15000

20000

25000

30000

35000

40000

0 10 20 30 40 50 60 70 80 90 100

stroke in %

e.g

. d

ecen

tra

lly c

losin

g v

alv

e w

ith

hyste

resis

Flo

w in

Nm

3/h

at

p1=

1.6

bar

ab

s, T

1 =

61°C

,

(p1-p

2)=

10m

ba

r

Ist-Durchfluß bei Hysterese + 15%

Soll-Durchfluß in Nm3/h

Ist-Durchfluß bei Hysterese - 15%

Hysteresis seriously disturb the entire control circuit

- in one position several flow values can appear,

caused by inconstant kv values

BS-956-04gb

Dat. 05.05.2003

actual flow with hysteresis +15%

nominal flow in Nm3/h

actual flow with hysteresis -15%

Emile Egger & Cie SA Cressier/NE (Suisse)