Example: Analog Value Processing With Fb250 And Fb251 - Siemens SIMATIC S5-90U System Manual

Analog Value Processing
12.3

Example: Analog Value Processing with FB250 and FB251

There are eight analog inputs and one analog output on the S5-95U
factory so that if no parameters are entered, the inputs can only be read in via a direct I/O access
(L PW). If you want to read in the inputs cyclically into the PII, you must first enter parameters in
DB1 (see Section 12.1).
Example: You can use a fan to help regulate the temperature in a room. The temperature
should fluctuate between 20 and 28 degrees Celsius (68 degrees Fahrenheit and
82 degrees Fahrenheit). The fan speed depends on the room temperature. You can
input the room temperature into FB250. You can output the setpoint value for the
fan speed in FB251.
Prerequisites:
• You have wired the analog connections (see Section 3).
• You have parameterized an analog input in the default DB1 ("AI1"; see Section 12.1),
transferred DB1 to the PLC and switched the PLC from STOP to RUN.
Reading in Analog Values (FB250)
In order to read in the analog value, call up FB250 on the programmer and enter its parameters as
they are shown in the example (see Table 12-17). Figure 12-2 shows you how the function block
operates. There is an explanation of the individual parameters in Table 12-18.
FB 250 reads in the analog values of analog input channel 0 cyclically and transfers an XA value to
the output in the range specified (scaled) by the user (see Figure 12-2).
12-14
S5-90U/S5-95U
.
The inputs are preset at the
EWA 4NEB 812 6115-02b