IAP Example-Adaptive Gain Control

If you want to know how to configure an AM or UCN adaptive gain strategy based on secondary controller status then this is the page for you.

Application

Consider a master flow controller cascaded onto three stream flow controllers. The gain of the master controller will need to be changed depending upon the number of stream controllers in cascade.

This is because if three stream controllers are in cascade the system has three times the gain as the case where one stream controller is in cascade.

Implementation

The master flow controller is configured as per normal except that the gain option needs to be changed to allow for a modulating gain factor. Thus set:

GAINOPT	EXT
KLIN	"value of gain for a single stream controller in cascade"
KEXT	initially 1 (will be set by adaptive gain strategy)

and the stream flow controllers are configured as per normal (adaptive gain effects the primary controller not the secondaries).

The adaptive gain is performed by a regulatory PV entity processing a summer algorithm. The specific configuration will be:

PVALGID	CALCULATOR
PISRC(1)	FC101A.CASMODFL
PISRC(2)	FC101B.CASMODFL
PISRC(3)	FC101C.CASMODFL
C1, C2, C3, C4	all 1
C	1
D	-4

The reason for D=-4 is that the summer algorithm is:

PVCALC = C * (C1*P1 + C2*P2 + C3*P3) + D

thus when there are two secondaries in cascade (P1 and P3):

PVCALC = 1 * ( 1*1 + 1*0 + 1*1) + (-4) = 2

and when there is one secondary in cascade PVCALC = 3.

This is because when there are three secondaries in cascade the gain of the system is three times as much as when there is one secondary in cascade. Thus the gain of the master controller needs to be one third as much as the case of the single secondary in cascade to maintain the overall gain of the system.

To get the adaptive gain to the master controller a logic slot entity will be needed (in the case of a UCN type configuration) or a general output connection (in the case of an AM type configuration).

In either case the PV of the regulatory PV is pushed to the KEXT parameter of the master controller.

Alternatives

It is possible to configure an adaptive gain for the situation above in a single logic entity. However as the number of secondaries increase the complexity of the logic required increases enormously. You will not get a count of how many secondaries are in CAScade mode either which may be important.