Description

Naming

Name in LL984 Editor	Function Block Name
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Function Description

The L9_PID2 function block implements an algorithm that performs proportional-integral-derivative operations. The algorithm tunes the closed loop operation in a manner similar to traditional pneumatic and analog electronic loop controllers. It uses a rate gain limiting (RGL) filter on the PV as it is used for the derivative term only, thereby filtering out higher-frequency PV noise sources (random and process generated).

Formula

Proportional Control

Proportional-Integral Control

Proportional-Integral-Derivative Control

Representation

Parameters

Input Pin	Name	Data Type	Address Range	Meaning
Top	AUTO	BOOL	–	0 = manual mode 1 = auto mode
Middle	TRACK	BOOL	–	0 = integral preload OFF 1 = integral preload ON
Bottom	REVERSE	BOOL	–	0 = output increases as E increases 1 = output decreases as E increases or output increases as E decreases

Node	Node Type	Name	Data Type	Address Range	Meaning
Top	IN/OUT	SOURCE	ARRAY[1...21] OF UINT, see Parameter SOURCE below	%MW	source first of 21 contiguous words in a source block
Middle	IN/OUT	DEST	ARRAY[1...9] OF UINT, see Parameter DEST below	%MW	destination first of 9 contiguous words used for L9_PID2 calculation NOTE: Do not load anything in these words.
Bottom	IN	INTERVAL	UINT	1... 255	solution interval Contains a number ranging from 1 ... 255, indicating how often the function will be performed. For more information see INTERVAL (Solution Interval) paragraph below.

Output Pin	Name	Data Type	Address Range	Meaning
Top	ERR	BOOL	–	1 = invalid user parameter or Loop ACTIVE but not being solved
Middle	HIGH	BOOL	–	1 = PV ≥ high limit indication
Bottom	LOW	BOOL	–	1 = PV ≤ low limit indication

INTERVAL (Solution Interval)

INTERVAL indicates that this is a L9_PID2 function block and contains a number ranging from 1 ... 255, indicating how often the function block will be performed. The number represents a time value in tenths of a second, for example, the number 17 indicates that the PID function block will be performed every 1.7 s.

Parameter SOURCE

The %MWx word entered in SOURCE is the first of 21 contiguous words. The contents of word 6 ... word 9 determine whether the operation will be P, PI, or PID.

Operation	Word 6	Word 7	Word 8	Word 9
P	ON	-	-	ON
PI	ON	ON	-	-
PID	ON	ON	ON	-

Word	Meaning	Content	Format
1	Scaled PV	loaded by the block each time it is scanned A linear scaling is done on %MWx + 13 using the high and low ranges from %MWx + 11 and %MWx + 12: scaled PV = (%MWx13 / 4095) * (%MWx11 - %MWx12) + %MWx12	UINT
2	SP	Specify the set point in engineering units. The value must be < value in word 12 and > value in word 13.	UINT
3	Mv	loaded by the block every time the loop is solved It is clamped to a range of 0 ... 4095, making the output compatible with an analog output module. The manipulated variable word may be used for further CPU calculations such as cascaded loops.	UINT
4	High Limit Indication	Load a value in this word to specify a high limit indication for PV (at or above SP). Enter the value in engineering units within the range specified in word 12 and word 13.	UINT
5	Low Limit Indication	Load a value in this word to specify a low limit indication for PV (at or below SP). Enter the value in engineering units within the range specified in word 12 and word 13	UINT
6	Proportional Band	Load this word with the desired proportional constant in the range 5 ... 500. The smaller the number, the larger the proportional contribution. A valid number is needed in this word for L9_PID2 to operate.	UINT
7	Reset Time Constant	Load this word to add integral action to the calculation. Enter a value between 0000 ... 9999 to represent a range of 00.00 ... 99.99 repeats/min. The larger the number, the larger the integral contribution. A value > 9999 stops the L9_PID2 calculation.	UINT
8	Rate Time Constant	Load this word to add derivative action to the calculation. Enter a value between 0000 ... 9999 to represent a range of 00.00 ... 99.99 min. The larger the number, the larger the derivative contribution. A value > 9999 stops the L9_PID2 calculation.	UINT
9	Bias	Load this word to add a bias to the output. The value must be between 000 ... 4095, and added directly to Mv, whether the integral term is enabled or not.	UINT
10	High Integral Windup Limit	Load this word with the upper limit of the output value (between 0 ... 4095) where the anti-reset windup takes effect. The updating of the integral sum is stopped if it goes above this value (this is normally 4095).	UINT
11	Low Integral Windup Limit	Load this word with the lower limit of the output value (between 0 ... 4095) where the anti-reset windup takes effect (this is normally 0).	UINT
12	High Engineering Range	Load this word with the highest value for which the measurement device is spanned, e.g. if a resistance temperature device ranges from 0 ... 500 degrees C, the high engineering range value is 500. The range must be given as a positive integer between 0001 ... 9999, corresponding to the raw analog input 4095.	UINT
13	Low Engineering Range	Load this word with the lowest value for which the measurement device is spanned. The range must be given as a positive integer between 0 ... 9998, and it must be less than the value in word 12. It corresponds to the raw analog input 0.	UINT
14	Raw Analog Measurement	The logic program loads this word with PV. The measurement must be scaled and linear in the range 0 ... 4095.	UINT
15	Pointer to LoopCounter Word	The value you load in this word points to the word that counts the number of loops solved in each scan. The entry is determined by discarding the most significant digit in the word where the controller will count the loops solved/scan, e.g., if the PLC does the count in word 41236, load 1236 into word 15. The same value must be loaded into word 15 in every L9_PID2 block in the logic program.	UINT
16	Maximum Number of Loops	solved in a scan If word 15 contains a non-zero value, you may load a value in this word to limit the number of loops to be solved in one scan.	UINT
17	Pointer To Reset Feedback Input	The value you load in this word points to the memory word that contains the value of feedback (F). Drop the 4 from the feedback word and enter the remaining digits in this word. Integration calculations depend on the F value being connected to Mv - i.e., as the PID2 output varies from 0 ... 4095, so should F vary from 0 ... 4095. If there is no external feedback, set this register to point to Mv (Word 3).	UINT
18	Output Clamp - High	The value entered in this word determines the upper limit of Mv (this is normally 4095).	UINT
19	Output Clamp - Low	The value entered in this word determines the lower limit of Mv (this is normally 0).	UINT
20	Rate Gain Limit (RGL) Constant	The value entered in this word determines the effective degree of derivative filtering. The range is from 2 ... 30. The smaller the value, the more filtering takes place.	UINT
21	Pointer to Integral Preload	The value entered in this word points to the memory word containing the track input (T) value. Drop the 4 from the tracking word and enter the remaining four digits in this word. The value in the T word is connected to the input of the integral lag whenever the auto bit and integral preload bit are both true.	UINT

Parameter DEST

The %MWy word entered in DEST is the first of 9 contiguous memory words used for L9_PID2 calculations. You do not need to load anything into these words.

Word	Meaning	Content	Format
1	Loop Status	12 of the 16 bits in this word are used to define loop status (see below).	UINT
2	Detected Error (E) Status Bits	This word displays L9_PID2 Detected Error Status Bits.	UINT
3	Loop Timer	This word stores the real-time clock reading on the system clock each time the loop is solved. The difference between the current clock value and the value stored in the word is the elapsed time. If elapsed time ≥ solution interval (10 times the value given in INTERVAL of the L9_PID2 block), then the loop should be solved in this scan.	UINT
4	for internal use	integral (integer portion)	INT
5	for internal use	integral-fraction 1 (1/3 000)	UINT
6	for internal use	integral-fraction 2 (1/600 000)	UINT
7	Pv x 8 (filtered)	This word stores the result of the filtered analog input (from %MWx13) multiplied by 8. This value is useful in derivative control operations.	UINT
8	Absolute Value of E	This word, which is updated after each loop solution, contains the absolute value of (SP - PV). Bit 8 in %MWy indicates the sign of E.	UINT
9	for internal use	current solution interval	UINT

Loop Status Word

Control Expert-IEC bits	Function
0	Bit 16 is set after initial startup or installation of the loop. If you clear the bit, the following actions take place in one scan: The loop status word %MWy is reset. The current value in the real-time clock is stored in word 3 of DEST (%MWy+2) Values in the fourth ... sixth words (%MWy+3,4,5) are cleared. The value in word 14 of SOURCE (%MWx+13) x 8 is stored in the sixth implied word (%MWy+6) The seventh and eighth implied words (%MWy+7,8) are cleared
1	top input status (MAN / AUTO)
2	middle input status (tracking mode) 1 = tracking 0 = no tracking
3	bottom input status (direct / reverse acting)
4	negative values in the equation
5	integral windup saturated
6	integral windup limit not set
7	rev B or higher
8	sign of E in %MWy + 7 0 = + (plus) 1 = - (minus)
9	%MWx14 word referenced by %MWx15 is valid.
10	loop in AUTO mode but not being solved
11	wind-down mod (for REV B or higher)
12	loop in AUTO mode and time since last solution ≥ solution interval
13	bottom output status (low limit exceeded)
14	middle output status (high limit exceeded)
15	top output status (parameter lockout or parameter detected error)