Using The Analog Input Filtering Instruction Wizard - Siemens Simatic S7-200 System Manual

Additional Features of STEP 7-Micro/WIN
5.3

Using the Analog Input Filtering Instruction Wizard

You can use the Analog Input Filtering Wizard to add an averaging routine to your program.
The S7-200 analog module is a high-speed module. It can follow rapid changes in the analog
input signal (including internal and external noise). Reading-to-reading variations caused by
noise for a constant or slowly changing analog input signal can be minimized by averaging a
number of readings. As the number of readings used in computing the average value
increases, a correspondingly slower response time to changes in the input signal can be
observed. An average value computed from a large number of samples can stabilize the
reading while slowing down its response to changes in the input signal.
Basic Filtering
To accomplish basic filtering, you need to answer three questions:
1. Which analog input do you wish to filter? (AIW0, AIW2, AIW4,...)
2. To what address should the filtered value be written? (VWx, AQWx, ...)
3. In what address do you want the scratchpad area for calculations to be placed? The
filtering code requires 12 bytes of data storage for calculations. (VBx, ...)
Additional Filtering Options
You can configure several options for more information about the analog input you are
monitoring,
Configurable Sample Size
Error Conditions
Specifying Input and Output
Specify which AIW is to be the input and where the output is to be written, as shown in
Figure 5-15. You can enter either an address or a symbol name for the output.
S7-200 Instruction Wizard (Analog Input Filtering)
Figure 5-15 Specifying Input and Output in the Analog Input Filtering Wizard
5-14
This formula will implement a filtering algorithm for analog inputs. It works by
sampling the input on each scan, and then averaging the values over a given
number of scans to increase stability. This average is output as the filtered value.
The wizard will also allow you to attach error-checking code to the output, so that
module errors can be recognized and handled.
Which Analog Input would you like to filter?
The filtered output may be written to a word location in V-memory or to an Analog
Output. You may specify a direct address, or a symbol name.
Where would you like the output written?
AIW0
''Filtered Out''
< Prev
Next>
S7-200 Programmable Controller System Manual
C79000-G7076-C230-02
Cancel