IAP Technique-Hand Station in Engineering Units

If you want to know how to configure a hand station in engineering units this is the page for you.

Summary

This technique uses an integral only controller with its output connected to its PV input connection. The user can then enter a SP and the controller will generate an output value in % that corresponds to the SP.

This will not happen instantaneously but will be governed by the integral action tuning constant. Normally this is acceptable and in most cases is even desirable.

Why use this technique

The most frequent application of this technique is for cases where a manually set signal is required for input to a control scheme and the input must be in engineering units. Using the standard Auto Manual algorithm requires the signal to be set in % and this is not very often intuitive.

Typical applications are:

Operator set constraint control

Implementation

The technique requires the building of a regulatory controller (UCN or AM) with the following specific parameter configurations:

PVEUHI	The high range value
PVEULO	The low range value
PVALGID	PID
CTLEQN	EqD (integral action only)
CTLACTN	Reverse
T1	see below
NOCINPTS	1
CISRC(1)	*.OPEU
NOCOPTS	0
OPEUHI	same value as PVEUHI
OPEULO	same value as PVEULO

Note the use of *.OPEU . That is what is actually entered as the configuration item. It means "my OPEU signal". Also the OPEUHI and OPEULO values have to be provided. Normally this are automatically set (except for PID-ERFB algorithm) by making them equal to the input range of the entity to which the controller is connected. Since there is no output connection in this case they need to be entered manually.

The value of T1 should be chosen according to how fast you want the output to attain the user entered value. Note that this loop cannot become unstable so even the maximum integral action (T1 = 0.03) will not cause problems. Typically values of 0.05 through 0.2 are suitable for most situations.

To use this in a scheme just pull in the .OPEU parameter from this controller into your scheme.

Alternatives

It is possible to use a numeric, an auto manual regulatory controller or a regulatory PV but there are several advantages that an integral only controller has over all of these.

I only Reg C

Numeric

Auto Man Reg C

Reg PV

Set in engineering units

Range limiting

Ability to ramp

Initialisation

Small resource usage

	I only Reg C	Numeric	Auto Man Reg C	Reg PV
Set in engineering units
Range limiting
Ability to ramp
Initialisation
Small resource usage