PLC外文翻译S7200的特性.docx

1、PLC外文翻译S7200的特性大学 毕业设计（外文翻译材料）2012年6月Features of the S7-200The S7-200 provides several special features that allow you to customize how the S7-200 functions to better fit your application.The S7-200 Allows Your Program to Immediately Read or Write the I/OThe S7-200 instruction set provides instructi

2、ons that immediately read from or write to the physical I/O. These immediate I/O instructions allow direct access to the actual input or output point, even though the image registers are normally used as either the source or the destination for I/O accesses.The corresponding process-image input regi

3、ster location is not modified when you use an immediate instruction to access an input point. The corresponding process-image output register location is updated simultaneously when you use an immediate instruction to access an output point.TipThe S7-200 handles reads of analog inputs as immediate d

4、ata, unless you enable analog input filtering. When you write a value to an analog output, the output is updated immediately.It is usually advantageous to use the process-image register rather than to directly access inputs or outputs during the execution of your program. There are three reasons for

5、 using the image registers: The sampling of all inputs at the start of the scan synchronizes and freezes the values of the inputs for the program execution phase of the scan cycle. The outputs are updated from the image register after the execution of the program is complete. This provides a stabili

6、zing effect on the system. Your program can access the image register much more quickly than it can access I/O points, allowing faster execution of the program. I/O points are bit entities and must be accessed as bits or bytes, but you can access the image register as bits, bytes, words, or double w

7、ords. Thus, the image registers provide additional flexibility.The S7-200 Allows Your Program to Interrupt the Scan Cycle If you use interrupts, the routines associated with each interrupt event are stored as part of the program. The interrupt routines are not executed as part of the normal scan cyc

8、le, but are executed when the interrupt event occurs (which could be at any point in the scan cycle).Interrupts are serviced by the S7-200 on a first-come-first-served basis within their respective priority assignments. The S7-200 Allows You to Allocate Processing Time for Run Mode Edit and Executio

9、n Status You can configure a percentage of the scan cycle to be dedicated for processing a run mode edit compilation or execution status. (Run mode edit and execution status are options provided by STEP 7-Micro/WIN to make debugging your program easier.) As you increase the percentage of time that i

10、s dedicated to these two tasks, you increase the scan time, which makes your control process run more slowly. The default percentage of the scan dedicated to processing run mode edits and execution status is set to 10%. This setting was chosen to provide a reasonable compromise for processing the co

11、mpilation and status operations while minimizing the impact to your control process. You can adjust this value by 5% increments up to a maximum of 50%. To set the scan cycle time-slice for background communications: 1.Select the View Component System Block menu command and select Background Time. 2.

12、In the Background tab, use the drop down box to select the communications background time.3.Click OK to save your selection.4. Download the modified system block to the S7-200.Figure 1 Communications Background TimeThe S7-200 Allows You to Set the States of Digital Outputs for Stop Mode The output t

13、able of the S7-200 allows you to determine whether to set the state of the digital output points to known values upon a transition to the STOP mode, or to leave the outputs in the state they were in before the transition to the STOP mode. The output table is part of the system block that is download

14、ed and stored in the S7-200. 1. Select the View Component System Block menu command and select Output Table. Click on the Digital tab. 2. To freeze the outputs in their last state, select the Freeze Outputs checkbox.3.To copy the table values to the outputs, enter the output table values by clicking

15、 the checkbox for each output bit you want to set to On (1) after a run-to-stop transition. The default values of the table are all zeroes. 4. Click OK to save your selections.5. Download the modified system block to the S7-200.Figure 2 Digital Output TableThe S7-200 Allows You to Configure the Valu

16、e of Analog Outputs The Analog Output Table allows you to set analog output points to known values after a RUN-to-STOP transition, or to preserve the output values that existed before the transition to STOP mode. The Analog Output table is part of the system block that is downloaded and stored in th

17、e S7-200 CPU. 1. Select the View Component System Block menu command and select Output Table. Click on the Analog tab. 2. To freeze the outputs in their last state, select the Freeze Outputs check box.3. The Freeze Values table allows you to set the analog outputs to a known value (-32768 to 37262),

18、 on a RUN-to-STOP transition. 4. Click OK to save your selections.5. Download the modified system block to the S7-200.Figure 3 Analog Output TableThe S7-200 Allows You to Define Memory to Be Retained on Loss of Power You can define up to six retentive ranges to select the areas of memory you want to

19、 retain through power cycles. You can define ranges of addresses in the following memory areas to be retentive: V, M, C, and T. For timers, only the retentive timers (TONR) can be retained. The default setting for the first 14 bytes of M Memory is to be non-retentive. Only the current values for tim

20、ers and counters can be retained: the timer and counter bits are not retentive. Tip Changing the range MB0 to MB13 to be retentive enables a special feature that automatically saves these locations to the permanent memory on power down.To define the retentive memory: 1.Select the View Component Syst

21、em Block menu command and select Retentive Ranges. 2. Select the ranges of memory to be retained following loss of power and click OK.3. Download the modified system block to the S7-200.Figure 4 Retentive MemoryThe S7-200 Allows You to Filter the Digital Inputs The S7-200 allows you to select an inp

22、ut filter that defines a delay time (selectable from 0.2 ms to 12.8 ms) for some or all of the local digital input points. This delay helps to filter noise on the input wiring that could cause inadvertent changes to the states of the inputs. The input filter is part of the system block that is downl

23、oaded and stored in the S7-200. The default filter time is 6.4 ms. As shown in Figure 4, each delay specification applies to groups of input points. To configure the delay times for the input filter: 1. Select the View Component System Block menu command and select Input Filters. Click on the Digita

24、l tab. 2. Enter the amount of delay for each group of inputs and click OK. 3. Download the modified system block to the S7-200. Tip The digital input filter affects the input value as seen by instruction reads, input interrupts, and pulse catches. Depending on your filter selection, your program cou

25、ld miss an interrupt event or pulse catch. The high speed counters count the events on the unfiltered inputs.The S7-200 Allows You to Filter the Analog Inputs The S7-200 allows you to select software filtering on individual analog inputs. The filtered value is the average value of a preselected numb

26、er of samples of the analog input. The filter specification (number of samples and deadband) is the same for all analog inputs for which filtering is enabled. The filter has a fast response feature to allow large changes to be quickly reflected in the filter value. The filter makes a step function c

27、hange to the latest analog input value when the input exceeds a specified change from the current value. This change, called the deadband, is specified in counts of the digital value of the analog input. The default configuration is to enable filtering for all analog inputs except AIW0 and AIW2 on C

28、PU 224XP. 1. Select the View Component System Block menu command and select Input Filters. Click on the Analog tab. 2. Select the analog inputs that you want to filter, the number of samples, and the deadband. 3. Click OK.4. Download the modified system block to the S7-200.Figure 5 Analog Input Filt

29、er Tip Do not use the analog filter with modules that pass digital information or alarm indications in the analog words. Always disable analog filtering for RTD, Thermocouple, and AS-Interface Master modules. Tip AIW0 and AIW2 on the CPU 224XP are filtered by the analog to digital converter, and usu

30、ally will not need the additional software filter.The S7-200 Allows You to Catch Pulses of Short DurationThe S7-200 provides a pulse catch feature which can be used for some or all of the local digital input points. The pulse catch feature allows you to capture high-going pulses or low-going pulses

31、that are of such a short duration that they would not always be seen when the S7-200 reads the digital inputs at the beginning of the scan cycle. When pulse catch is enabled for an input, a change in state of the input is latched and held until the next input cycle update. This ensures that a pulse

32、which lasts for a short period of time is caught and held until the S7-200 reads the inputs.You can individually enable the pulse catch operation for each of the local digital inputs.To access the pulse catch configuration screen:1. Select the View Component System Block menu command and select Pulse Catch Bits.2. Click the corresponding check box and click OK.3. Download the modified system block to the S7-200.Figure 6 Pulse CatchFigure 7 show