Файл: Industrial Control (Students guide, 1999, v1.1 ).pdf

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We'll discuss operation and major blocks in our code. At the top of the code is the initialization information:

'******************************************************

This data defines the time to set the RTC, how long the interval between logging should be, and how many samples should be logged. Stop_Reset is defines whether to stop logging (1) or reset (0) and start over destroying the old data when the maximum samples are collected.

The pushbutton has several purposes:

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1.On-Power up or Reset of the BS2, a message will appear informing you to hold down the pushbutton to initialize the clock and logging (the LED will light for this also). If the button is held down, the value of time in the initialization section will be used to set the RTC and logging will be reset to the start. Recovery data will be written to EEPROM for the next reset.

2.During logging, if the pushbutton is pressed, the data will be ‘dumped’ or downloaded. We will be using StampPlot Lite to capture and plot the data as it is dumped. The data is NOT destroyed and the logger will continue to log new data.

3.At the end of a data dump, if the pushbutton is held down, the data logger will reset the log to the start destroying old data and resetting the start time of logging.

If the BASIC Stamp 2 is reset and the button is NOT held down, the program will read recovery data of current memory location and start time from the EEPROM. The RTC time will NOT be reset. It should be maintaining proper time through the reset UNLESS power was lost. Figure 7.7 is the flowchart of the initialization of the program.

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Figure 7.7: Logging Initialization Routine

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Figure 7.8: Control and Saving Routines

Time Control routine (Figure 7.8) is used to determine if it is time to save new data to memory. This is contingent on the memory location for samples being less than the number of samples specified.

TimeControl: ' Check if time for reading IF (Time = LTime) AND (MemAddr-4 < Samples) THEN SaveData

RETURN

The Save Data routine is called from Time Control when it is time to write a new sample to memory. The current DataIn (value read from the ADC) is stored in the current memory address, and the memory address is incremented for the next cycle. The next interval time is calculated (and later BCD adjusted). If the

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maximum number of samples is reached, depending on the Stop_Reset value, data logging will either ceased (see Time Control) or logging will start over.

Note that the raw DataIn value from the ADC is stored and not the temperature-calculated value. This allows the data to be stored in one byte instead of two as a word. The stored value will be converted into temperature when it is ‘dumped’ to the PC.

Figure 7.9 illustrates the flow of the DumpData routine. When the pushbutton is pressed, Dump Data configures StampPlot for plotting, and creates a loop reading through the logged values, converting them to temperatures, and sending the values for plotting and the message window. Note that the log time is set to the start time, and the timing interval is added to the log time each loop iteration to determine the original time the data was logged.

Once the loop is complete, the log time is set back to the current time and the user is requested to hold down the pushbutton to reset the logging to start (the LED will light for indication also).

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Figure 7.9: Data Dump Routine Flowchart

Once DumpData is complete, the control time will be updated to the time of the next sample, and logging will continue from the point it left off, allowing downloading without affecting the stored data. Figure 7.10a is a screenshot of our collected data dumped to StampPlot Lite.

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Figure 7.10a: Sample Data Dump of Logged Data

The format of the message data is suitable for importing into a spreadsheet for graphing, as seen in Figure 7.10b. A portion of the saved message file is as follows:

Point,Time,Temperature

0,22:51,787

1,22:56,787

2,23:01,787

3,23:06,787

4,23:11,783

5,23:16,783

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Figure 7.10b: Imported Message Data to Excel

We set the incubator outside of a window and recorded outdoor temperatures.. Outdoor temperature can be tricky due to effects of wind cooling, sunlight heating, and thermal layers in the canister trapping heat. We had quite a few spikes in readings. Can you do better?

Our plot shows temperatures from 22:51 to 22:51 the next night. Note the rise and falls in temperature during the day. The expected high for the day was 88F, and we came pretty close!

Of course, we are not restricted s temperature range 70F-120F. Refer back to Experiment #4. Software range values are determined by the span and offset voltage settings to the ADC0831.

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Questions and Challenges:

1.Perform Logging of a System: Determine a temperature that you want to log over a long period of time. This may be outdoors, the room temperature (does the heating/cooling change during evening hours?), or maybe some other slow changing system (a water tank in the sun?).

1)Determine the range of expected values for temperature. Set the span and offset variables and potentiometers appropriately.

2)Determine the length of time you need to collect the data (one day? the weekend?). Based on a maximum of 50 samples, calculate the interval time needed for logging.

3)Ready to program? If you are going to move your BOE, make sure it is running on a battery that will last throughout the logging!

4)We also want to check the accuracy of the RTC in this experiment, so when the program is ready to download:

a)Open the Windows clock and pick an upcoming time.

b)Set the start time to this upcoming time (remember to use 24-hour time) Time = $1530

c)5 seconds before the initializing time, download the file to the BS2 and hold the circuit pushbutton down until the LED goes off or debug window instructs you to release it.

d)Use the Debug Window or StampPlot to note the BS2 and the PC Times.

BS2: _________ PC: __________ Difference: ________

e)Let your data record! After the 1st sample is done, you may test the data dump by pressing the push-button.

f)After you are finished recording data, run and connect StampPlot Lite, press the push-button to dump the data.

g)Use the Debug Window or StampPlot to note the BS2 and the PC Time.

BS2:_________ PC: __________ Difference: ________

h) Extrapolate the time-error for 24 hours: _________

Did the data conform to your expectations?

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2.Discuss the 'system' you monitored and conclusions of your results.

3.How much time error was calculated over a 24-hour period? How could this error be compensated for in software?

4.Why is it important to limit the amount of data that can be stored in the BS2?

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Appendix A: StampPlot Lite

Downloading and Installing StampPlot Lite

StampPlot Lite may be downloaded from the Stamps in Class web site at http://www.stampsinclass.com. The program is installed by double-clicking on the setup.exe icon and accepting the default directories.

To download StampPlot Lite, click on the “Downloads” button on our web site and scroll down to the “Industrial Control” section.

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