L9P_RMPLN: Logarithmic Ramp to Set Point

Naming

Name in LL984 Editor	Function Block Name
name of legacy 984 instruction	name in other tools and editors like: Type Library Browser Data Editor Animation Tables Search Results

Function Description

The L9P_RMPLN DFB allows you to ramp up logarithmically to a target set point at a specified approach rate. At each successive call, it calculates the output until it is within a specified deadband (DB). DB is necessary because the incremental distance the ramp crosses decreases with each solve.

You need to specify:

the target set point, in the same units as the contents of the input words are specified
the sampling rate
the time constant used for the logarithmic ramp, which is the time it takes to reach 63.2% of the new set point

You should use a t that is ≥4 *Δt. This will help to ensure sufficient granularity in the output response.

You may use a flag to initialize after an undetermined down-time. The DFB will store a new sample, then wait for one cycle to collect the second sample. Calculations will be skipped for one cycle and the output will be left as is, after which the ramp will resume.

Representation

Parameters

Input Pin	Name	Data Type	Address Range	Meaning
Top	ENABLE	BOOL	–	ON = enables process control function

Node	Node Type	Name	Data Type	Address Range	Meaning
Middle	IN/OUT	PAR	ARRAY[1...16] OF UINT	%MW	see Parameter PAR below
Bottom	IN	LEN	UINT	16	length of parameter block (can not be changed)

Position	Name	Data Type	Address Range	Meaning
Top	OUT	BOOL	–	ON = operation successful
Bottom	ERR	BOOL	–	ON = operation not successful

Parameter PAR

The data type of the parameter block is ARRAY[1...16] of UINT

Word	Content	Format
1, 2	set point (input)	REAL (Floating Point)
3	output status	UINT
4	input status	UINT
5	time word	UINT
6	reserved	UINT
7, 8	time (in ms) since last solve	DINT
9, 10	solution interval (in ms)	DINT
11, 12	time constant, τ, (per second) of exponential ramp toward the target set point	REAL (Floating Point)
13, 14	deadband (DB) in engineering units	REAL (Floating Point)
15, 16	output	REAL (Floating Point)

Output Status

Control Expert-IEC bits	Function
0...7	standard output bits (flags)
8	1 = ramping up
9	1 = ramping down
10	1 = ramp complete 0 = ramp in progress
11	1 = DB or τ set to negative units
12...15	not used

Input Status

Control Expert-IEC bits	Function
0...11	not used
12...15	standard input bits (flags)