With reference to pneumatically operated control valves: (a) State FOUR reasons for fitting a valve positioner (4) (b) Explain valve hysteresis, stating how it affects the process (2) (c) State the immediate action to be taken to restore control upon failure of the positioner bellows (2) (d) State the difference between fail safe and fail set (2)
Control system
UKM Tuticorin 
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