Tank level in STL

TopicTank level in STL

Title

The tank's volume from its level transmitter

ExampleW06.1

Step1 / 4

Mode

Given

An S7-300 reads a horizontal cylindrical tank's level transmitter at PIW 256 and works out the volume, network by network, in the STL listing below. For each raw value, fill in the corrected value in MW 20, the level $h$ , the wetted area $A$ and the volume $V$ .

$r = 1.0\ \text{m}$ , tank length $4.0\ \text{m}$
raw $0$ to $27648$ is empty to full
zero-point offset $200$

Each network in turn, three raw values

PIW 256	MW 20	$h$ m	$A$ m²	$V$ l
6712	6912
13624	13824
20536	20736

Correct the zero point

Network 1 adds the offset with

+I

13624 + 200 = 13824

. An INT sum past

32767

would wrap and set OV, which latches M 1.2.

Sim

The tank listing, running

Set the level transmitter's raw value and the switches, then step a statement or run a whole scan. The trace shows the accumulators, AR 1, the status word and every byte each statement writes.

ORGANIZATION_BLOCK OB 1
TITLE = Horizontal cylindrical tank: level to volume
// Tank radius r = 1.0 m, length 4.0 m.
// PIW 256: level transmitter, 0..27648 = empty..full (-27648..27648 if I 0.1 = bipolar).
// MD 60..72: four volume set-points in litres, written by the HMI.
BEGIN
NETWORK
TITLE = 1 Zero-point correction
L PIW 256 // raw level from the analog module
L 200 // zero-point offset found at commissioning
+I // INT add: wraps past 32767 and sets OV
T MW 20 // corrected raw level
A OV // did the addition overflow?
S M 1.2 // latch: offset overflow alarm
NETWORK
TITLE = 2 Scale to metres with FC105
CALL FC 105
IN :=MW20
HI_LIM :=2.000000e+000 // full = tank diameter, 2.0 m
LO_LIM :=0.000000e+000 // empty = 0.0 m
BIPOLAR:=I0.1
RET_VAL:=MW22 // W#16#0008 = input out of range
OUT :=MD24 // level h in metres
NETWORK
TITLE = 3 Wetted cross-section: A = r2 acos(d/r) - d sqrt(2rh - h2)
L 1.000000e+000 // r = 1.0 m
T MD 12
L MD 12
L MD 24
-R // d = r - h
T MD 44
L MD 12
/R // d / r
ACOS // half the wetted angle, rad
L MD 12
SQR // r squared
*R
T MD 48 // r2 acos(d/r)
L MD 12
L 2.000000e+000
*R // 2r
L MD 24
*R // 2rh
L MD 24
SQR // h squared
-R
ABS // clears -0.0 when h = 0 or h = 2r
SQRT // half the chord
L MD 44
*R // d sqrt(2rh - h2)
T MD 52
L MD 48
L MD 52
-R // wetted area A, m2
T MD 28
NETWORK
TITLE = 4 Volume in litres
L MD 28
L 4.000000e+000 // tank length 4.0 m
*R
L 1.000000e+003 // m3 to litres
*R
T MD 32 // volume V, litres
NETWORK
TITLE = 5 Level band: how many set-points has V passed?
L 0
T MW 36 // band := 0
LAR1 P#60.0 // AR1 -> first set-point, MD 60
L 4 // four set-points
NEXT: T MW 38 // loop counter
L MD 32 // volume
L MD [AR1,P#0.0] // set-point under AR1
>R
JCN SKIP
L MW 36
L 1
+I
T MW 36 // band := band + 1
SKIP: +AR1 P#4.0 // next set-point
L MW 38
LOOP NEXT
L MW 20
L 10
*I // tenths of a count, 32 bits, for the trend log
T MD 40
NETWORK
TITLE = 6 Alarms, latched until I 0.0 acknowledges
A I 0.0 // acknowledge button
R M 1.0
R M 1.1
R M 1.2
L MW 22 // RET_VAL from FC105
L 0
<>I
S M 1.0 // latch: level signal out of range
L MW 36 // level band
L 4
>=I
S M 1.1 // latch: above the high-high set-point
O M 1.0
O M 1.1
O M 1.2
= Q 4.1 // common alarm lamp
NETWORK
TITLE = 7 High-volume lamp (exam trap)
A I 0.2 // pump running: opens a logic string ...
L MD 32
L 1.000000e+004
>R // ... but a compare writes RLO outright
= Q 4.0 // so Q 4.0 = (V > 10 000 l), whatever I 0.2 is
END_ORGANIZATION_BLOCK

PIW 256 (INT)

Scan 1 · statement 113 of 113

Statement111 BE

ACCU 110000.016#461C_4000

ACCU 26283.185516#45C4_597C

AR 1P#76.0

/FC0
RLO0
STA1
OR0
OS0
OV0
CC01
CC10
BR?

A ? is left by FC105: Siemens doesn't publish what the block leaves there, so the trace doesn't guess until a statement writes it.

Writtennothing

Operand	Value
MW 20	13824
MW 22	W#16#0000
MD 24	1.0
MD 28	1.5707964
MD 32	6283.1855
MW 36	2
MD 40	L#138240
Q 4.0	0
Q 4.1	0
M 1.0	0
M 1.1	0
M 1.2	0

Line	Statement	ACCU 1	RLO
9	L PIW 256	13624	0
10	L 200	200	0
11	+I	13824	0
12	T MW 20	13824	0
13	A OV	13824	0
14	S M 1.2	13824	0
17	CALL FC 105	?	?
26	L 1.000000e+000	1.0	?
27	T MD 12	1.0	?
28	L MD 12	1.0	?
29	L MD 24	1.0	?
30	-R	0.0	?
31	T MD 44	0.0	?
32	L MD 12	1.0	?
33	/R	0.0	?
34	ACOS	1.5707964	?
35	L MD 12	1.0	?
36	SQR	1.0	?
37	*R	1.5707964	?
38	T MD 48	1.5707964	?
39	L MD 12	1.0	?
40	L 2.000000e+000	2.0	?
41	*R	2.0	?
42	L MD 24	1.0	?
43	*R	2.0	?
44	L MD 24	1.0	?
45	SQR	1.0	?
46	-R	1.0	?
47	ABS	1.0	?
48	SQRT	1.0	?
49	L MD 44	0.0	?
50	*R	0.0	?
51	T MD 52	0.0	?
52	L MD 48	1.5707964	?
53	L MD 52	0.0	?
54	-R	1.5707964	?
55	T MD 28	1.5707964	?
58	L MD 28	1.5707964	?
59	L 4.000000e+000	4.0	?
60	*R	6.2831855	?
61	L 1.000000e+003	1000.0	?
62	*R	6283.1855	?
63	T MD 32	6283.1855	?
66	L 0	0	?
67	T MW 36	0	?
68	LAR1 P#60.0	0	?
69	L 4	4	?
70	T MW 38	4	?
71	L MD 32	6283.1855	?
72	L MD [AR1,P#0.0]	1000.0	?
73	>R	1000.0	1
74	JCN SKIP	1000.0	1
75	L MW 36	0	1
76	L 1	1	1
77	+I	1	1
78	T MW 36	1	1
79	+AR1 P#4.0	1	1
80	L MW 38	4	1
81	LOOP NEXT	3	1
70	T MW 38	3	1
71	L MD 32	6283.1855	1
72	L MD [AR1,P#0.0]	3000.0	1
73	>R	3000.0	1
74	JCN SKIP	3000.0	1
75	L MW 36	1	1
76	L 1	1	1
77	+I	2	1
78	T MW 36	2	1
79	+AR1 P#4.0	2	1
80	L MW 38	3	1
81	LOOP NEXT	2	1
70	T MW 38	2	1
71	L MD 32	6283.1855	1
72	L MD [AR1,P#0.0]	10000.0	1
73	>R	10000.0	0
74	JCN SKIP	10000.0	1
79	+AR1 P#4.0	10000.0	1
80	L MW 38	2	1
81	LOOP NEXT	1	1
70	T MW 38	1	1
71	L MD 32	6283.1855	1
72	L MD [AR1,P#0.0]	12000.0	1
73	>R	12000.0	0
74	JCN SKIP	12000.0	1
79	+AR1 P#4.0	12000.0	1
80	L MW 38	1	1
81	LOOP NEXT	0	1
82	L MW 20	13824	1
83	L 10	10	1
84	*I	L#138240	1
85	T MD 40	L#138240	1
88	A I 0.0	L#138240	0
89	R M 1.0	L#138240	0
90	R M 1.1	L#138240	0
91	R M 1.2	L#138240	0
92	L MW 22	0	0
93	L 0	0	0
94	<>I	0	0
95	S M 1.0	0	0
96	L MW 36	2	0
97	L 4	4	0
98	>=I	4	0
99	S M 1.1	4	0
100	O M 1.0	4	0
101	O M 1.1	4	0
102	O M 1.2	4	0
103	= Q 4.1	4	0
106	A I 0.2	4	1
107	L MD 32	6283.1855	1
108	L 1.000000e+004	10000.0	1
109	>R	10000.0	0
110	= Q 4.0	10000.0	0
111	BE	10000.0	0

Worked examples

The tank's volume from its level transmitter

Correct the zero point

The tank listing, running