Siemens Simatic S7-200 CPU 210, System Manual

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4-16
S7-200 Programmable Controller, CPU 210
C79000-G7076-C235-01
4.7 Using the Analog Adjustment Potentiometer
As shown in Figure 4-15, your CPU 210 provides one analog adjustment potentiometer
(located under the access cover of the module). You can adjust this potentiometer to
increase or decrease values which are stored in bytes of Special Memory (SMW2). Your
program can use this read-only value for a variety of functions, such as updating the current
value for a timer or a counter, entering or changing the preset values, or setting limits.
You use a small screwdriver to make the adjustments: turn the potentiometer clockwise (to
the right) to increase the value, and counter-clockwise (to the left) to decrease the value.
Analog Adjustment
potentiometer
M L+ 0.0 0.1 0.2 0.3
DC
OUTPUTS
↓
M L+ 24V DC
Figure 4-15 Analog Adjustment Potentiometer
SMW2 stores the digital value that represents the position of the analog adjustment
potentiometer.
The CPU 210 samples the analog adjustment potentiometer at least three times a second
and has a range from 0 to 255. The new value of the analog adjustment potentiometer is
written to SMW2 at the beginning of the next scan.
The analog adjustment potentiometer on the PDS 210 has a nominal range of 0 to 255, with
a guaranteed range of 10 to 200.
Figure 4-16 shows a sample program that uses the value entered with the analog adjustment
potentiometer.
STL
Network 1
LD
I0.0
MOVW SMW2, MW0
Network 2
LDN
M2.0
TON T0, 0
Network 3
LDW>=
T0, MW0
= M2.0
Read the analog adjustment
value and store that value in
MW0
.
Start timer T0.
LAD
Turn on
M2.0
when
T0
reaches the value entered
with the analog adjustment.
M2.0
T0
>=I
MW0
M2.0
/
Network 1
MOV_W
EN
IN OUT SMW2 MW0
I0.0
TON
IN
PT
T0
+0
Network 2
Network 3
Figure 4-16 Sample Program for Using the Analog Adjustment
Basic Concepts for Programming the CPU 210