122-28176 Parallax Inc, 122-28176 Datasheet - Page 133

• Manufacturer Part Number: 122-28176
• Description: GUIDE STUDENT PROCESS CONTROL
• Manufacturer: Parallax Inc

Specifications of 122-28176

• Accessory Type: Manual
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: Propeller Education (PE) Kit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant

Increasing the count sample time leads to greater accuracy and resolution. The best
resolution occurs when the count is obtained over a full 60 seconds giving a very accurate
value for RPM. What problem does this introduce? If the BASIC Stamp is controlling or
monitoring the system, will a 60 second pause in control be a detriment? A process
control system may require fast sample times to ensure reliable control.
Test the response and resolution of measuring the fan's RPM by changing the Sample
Time in StampPlot (and tabbing off). Complete Table 4-3 by entering the specified
Sample Time in StampPlot and completing the table for 2 values of RPM. Calculate the
resolution - the change in RPM per count. An example entry is completed for you:
Figure 4-22 shows a plot using various sample times. Note the amount of change in
RPM resolution for the various sample times. A small change in counts resulted in a very
large change for RPM.
Time, ms
Sample
10000
1000
1000
2000
5000
500
200
100
50
Resolution= (change in RPM)/(change in Count) = (8100−8040)/(135−134) = 60
This waveform was captured using the circuit in the next activity. Effects of loading
lowered the metered voltage significantly due to the high impedance output of the circuit
(RC = 1MΩ) and the impedance input of the oscilloscope used for waveform capture.
Count
135
Table 4-3: Resolution and Sample Time
RPM
8100
Count
134
RPM
8040
Resolution
in RPM
60