CR200/CR200X Series Dataloggers - Campbell Scientific

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Section 4. Sensor Support 4.3.1 Measurements Requiring AC Excitation Some resistive sensors require AC Excitation. These include electrolytic tilt sensors, soil moisture blocks, water conductivity sensors, and wetness sensing grids. The use of DC excitation in these sensors can result in polarization, which will cause erroneous measurement, shift calibration, or lead to rapid sensor decay. Other sensors, e.g., LVDTs (Linear Variable Differential Transformer), require and AC excitation because they rely on inductive coupling to provide a signal. DC excitation will provide no output. CR200(X) bridge measurements cannot reverse excitation polarity to provide AC excitation and avoid ion polarization. Sensors requiring AC excitation should not be used with the CR200(X). Other Campbell Scientific dataloggers (e.g. CR800 series, CR1000, CR3000) are compatible with sensors that require AC excitation. 4.4 Pulse Count Measurement FIGURE. Switch Closure Pulse Sensor p. 42 is a generalized schematic showing connection of a pulse sensor to the CR200(X). The CR200(X) features two dedicated pulse input channels, P_SW and P_LL, and two digital I/O channels, C1and C2, for measuring pulse output sensors. Activated by the PulseCount () instruction, dedicated 16-bit counters on P_SW, P_LL, C1 and C2 are used to accumulate all counts over the user specified scan interval. The value which is output for each scan is the difference in the last known counter value and the new counter value. Since the last count is maintained for each scan, even if the counter rolls over between scans the correct count will be recorded. If the time between scans is such that the counter exceeds 65,536 pulses during a scan, then the counter will roll over twice resulting is an erroneous measurement. PulseCount () instruction parameters specify the pulse input type, channel used, and pulse output option. Note: The PulseCount instruction must be executed once before the pulse or control port is ready for input. This may be of particular concern for programs with long scan intervals. For example, the PulseCount () instruction will not yield a valid output until the turn of the second hour if the PulseCount () instruction is used within a program with a scan interval of 1 hour. Figure 29: Switch Closure Pulse Sensor 42
Section 4. Sensor Support Note: The PulseCount () instruction should not be used in a conditional statement or subroutine. To ensure all pulses are detected, it must be executed each scan. Execution of PulseCount () within a scan involves determining the accumulated counts in each dedicated 16-bit counter since execution of the last PulseCount (). PulseCount () parameter (POption) determines if the output is in counts (POption = 0) or frequency (POption = 1). Counts are the preferred output option for measuring number of tips from a tipping bucket rain gage, or the number of times a door opens. Many pulse sensors, such as anemometers and flow meters, are calibrated in terms of frequency (Hz or counts / second), and are usually measured with the frequency option. Resolution of the pulse counters is one count. Resolution of frequency is (1/scan interval). For example, the frequency resolution of PulseCount() returning a result every 1 second is 1 Hz. The resultant measurement will bounce around by the resolution. For example, if you are scanning a 2.5 Hz input once a second, in some intervals there will be 2 counts and in some 3. If the pulse measurement is averaged, the correct value will be the result. Accuracy is limited by a small scan interval error of ±(3 ppm of scan interval + 10 µs) plus the measurement resolution error of ± 1 Hz. The sum is essentially ± 1 Hz. Extending a 1 second measurement interval to 10 seconds, either by increasing the scan interval or by averaging, improves the resulting frequency resolution from 1 Hz to 0.1 Hz. Averaging can be accomplished by the Average () instruction or by computing a running or spatial average through programming. 4.4.1 Pulse input Channels Read More! Review pulse counter specifications p. 35. Review pulse counter programming in CRBASIC Help for the PulseCount () instruction. 43
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OPERATOR’S MANUAL CR200/CR200X Se
Page 4 and 5: Assistance Products may not be retu
Page 6 and 7: Table of Contents 4.4 Pulse Count M
Page 8 and 9: Table of Contents 11.4.3 SDI-12 Pow
Page 10 and 11: Table of Contents Index ...........
Page 12 and 13: Table of Contents CRBASIC EXAMPLE 1
Page 14 and 15: Section 1. Introduction Table 1. CR
Page 16 and 17: Section 2. Quickstart Tutorial 2.1.
Page 20 and 21: Section 2. Quickstart Tutorial Figu
Page 24 and 25: Section 2. Quickstart Tutorial Exam
Page 26 and 27: Section 2. Quickstart Tutorial 2. A
Page 34 and 35: Section 2. Quickstart Tutorial 22
Page 36 and 37: Section 3. Overview Figure 25: Feat
Page 38 and 39: Section 3. Overview Period Average:
Page 40 and 41: Section 3. Overview 3.1.3.4 Power T
Page 42 and 43: Section 3. Overview 3.1.5.1 Firmwar
Page 44 and 45: Section 3. Overview Advantages of P
Page 46 and 47: Section 3. Overview Table 3. Intern
Page 48 and 49: Section 3. Overview 36
Page 50 and 51: Section 4. Sensor Support 4.1.3 Swi
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Page 56 and 57: Section 4. Sensor Support FIGURE. P
Page 58 and 59: Section 4. Sensor Support 4.6 SDI-1
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Page 62 and 63: Section 5. Measurement and Control
Page 64 and 65: Section 5. Measurement and Control
Page 66 and 67: Section 6. CR200(X) Power Supply Au
Page 68 and 69: Section 7. Grounding 7.1.1 Lightnin
Page 70 and 71: Section 7. Grounding Examples: •
Page 72 and 73: Section 8. CR200(X) Configuration F
Page 74 and 75: Section 8. CR200(X) Configuration T
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Page 78 and 79: Section 8. CR200(X) Configuration
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Page 82 and 83: Section 9. Programming in the Logge
Page 84 and 85: Section 9. Programming 9.5 Structur
Page 86 and 87: Section 9. Programming Variable nam
Page 88 and 89: Section 9. Programming CRBASIC EXAM
Page 90 and 91: Section 9. Programming DataTable ()
Page 94 and 95: Section 9. Programming Consider the
Page 96 and 97: Section 9. Programming Scan () dete
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Section 9. Programming 92
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Section 10. CRBASIC Programming Ins
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Section 11. Programming Resource Li
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Section 12. Memory and Data Storage
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Section 13. Telecommunications and
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Section 14. PakBus Overview • Rou
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Section 14. PakBus Overview 14.4.6
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Section 14. PakBus Overview 14.5.3
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Section 15. Alternate Telecoms Reso
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Section 15. Alternate Telecoms Reso
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Section 16. Support Software 16.4 P
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Section 16. Support Software 146
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Section 17. Care and Maintenance Fi
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Section 17. Care and Maintenance 15
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Section 18. Troubleshooting 18.1.1.
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Section 18. Troubleshooting Table 2
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Section 18. Troubleshooting 18.3.3
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Section 18. Troubleshooting 18.3.3.
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Section 18. Troubleshooting 160
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Appendix A. Glossary baud rate sett
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Appendix A. Glossary Earth Ground u
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Appendix A. Glossary modem/terminal
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Appendix A. Glossary period average
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Appendix A. Glossary the table is e
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Appendix A. Glossary VAC Volts Alte
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Appendix A. Glossary 14
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Appendix B. Status Table and Settin
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Appendix C. Serial Port Pin Outs 22
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Appendix D. ASCII / ANSI Table Dec
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Appendix D. ASCII / ANSI Table Dec
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Appendix F. Sensors and Peripherals
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Index Debugging • 151 Declaration
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Index O Offset • 86 Ohm • 6 Ohm
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Index U UPS • 11 User Program •
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CR200/CR200X Series Dataloggers - Campbell Scientific

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