Campbell Scientific CSAT3 CSAT3 3-D Sonic Anemometer - Page 68

Appendix D. SDM Communications and Long Signal Cables D.2 CR3000 Example Connect all the SDM devices to the datalogger with the cable in question. Download the example CRBasic SDM search program to the datalogger. This program will test the SDM communications between a CRBasic datalogger and a CSAT3, LI-7500, or both a CSAT3 and LI-7500. After the program compiles, use the CRBasic keyboard and set the menu items "Test CSAT3?" and "Test LI-7500?" to the appropriate values. To start the test, set the menu item "Start Test?" to "Yes". The test is complete when the menu item "Start Test?" is reset to "No". The test makes about 3,000 attempts to communicate with the SDM devices. With the CR3000 and CR5000 the test takes about 5 minutes to complete. With the CR1000 the test takes about 25 minutes to complete. To terminate the test before the test is complete, set the menu option "Start Test?" to "No". Collect the data table "report". Take the following case, a 100 m (328.1 ft) SDM signal and power cable is used to connect a CR3000 datalogger and a single CSAT3 anemometer. Communication between the CR3000 and CSAT3 fails at the default SDM bit period of 30 µSec. Thus, a longer SDM bit period (slower SDM clock rate) must be used. The example CR3000 SDM clock rate search program generated the data in TABLE D-1. TABLE D-1. Data from Example CR3000 SDM Clock Rate Search Program TOA5, CR3000_usb, CR3000, 1138, CR3000.Std.05.02, CPU:Sdm_cr3kv1_3.cr3, 21566, report RECORD SDM_Period All_Fail_Tot CSAT_sig_Tot CSAT_NaN_Tot IRGA_sig_Tot IRGA_NaN_Tot Number_Attempts CSAT3 LI-7500 RN uSec samples samples samples samples samples unitless Smp Smp Smp Smp Smp Smp Smp Smp Smp 0 30 2 2 0 0 20 0 2984 1 10 1 40 0 0 0 0 0 2 1 10 2 50 0 0 0 0 0 2 1 10 3 60 0 0 0 0 0 2 1 10 From the results in TABLE D-1, the shortest bit period (fastest SDM clock rate) that the SDM bus could run, without encountering communication errors, would be with a bit period of 40 µSec. However, to have a safety margin, a value of 50 µSec is used for the SDM bit period. The SDM bit period was set to 50 µSec and tested the system program. The test showed that using a SDM bit period of 50 µSec, in the SDMSpeed () instruction, did not cause the CR3000 to skip scans (Status Table), thus the SDM bit period is left at parameter 50 µSec. D.3 CR23X Example Connect all the SDM devices to the datalogger with the cable in question. Download the example CR23X SDM search program to the datalogger, after the program compiles, set Flag 3 high to begin the experiment. When Flag 2 is set low the experiment is complete. The test makes 3,600 attempts to communicate with the SDM device at a frequency of 10 Hz. The test takes 3 minutes to run. Collect the data from the datalogger and run the example SPLIT parameters files, SDM_TRAN.PAR and SDM.PAR, to sort the data. Identify the correct SDM clock parameter to use for your system configuration from the report generated by the SPLIT parameter file SDM.PAR. D-2