Campbell Scientific CR10X TD Operating System Addendum for CR510, CR10X, and C - Page 27

TD ADDENDUM-SECTION 2. INTERNAL DATA STORAGE The Timestamp and record number labels are added automatically. 2.2 DATA OUTPUT FORMAT AND RANGE LIMITS Data is stored internally in Campbell Scientific's Binary Final Storage Format (Appendix C.2). Data may be sent to Final Storage in either LOW RESOLUTION or HIGH RESOLUTION format. 2.2.1 RESOLUTION AND RANGE LIMITS Low resolution data is a 2 byte format with 4 significant digits and a maximum magnitude of +7999. High resolution data is a 4 byte format (see Section 2.2.2). TABLE 2.2-1. Resolution Range Limits of CR10 Data Minimum Resolution Zero Magnitude Low High 0.000 + 0.001 0.0000 1x10-19 Maximum Magnitude +7999. +9x10+18 The resolution of the low resolution format is reduced to 3 significant digits when the first (left most) digit is 8 or greater. Thus, it may be necessary to use high resolution output or an offset to maintain the desired resolution of a measurement. For example, if water level is to be measured and output to the nearest 0.01 ft., the level must be less than 80 ft. for low resolution output to display the 0.01 ft. increment. If the water level was expected to range from 50 to 90 feet the data could either be output in high resolution or could be offset by 20 ft. (transforming the range to 30 to 60 ft.). 2.2.2 HIGH RESOLUTION FINAL STORAGE DATA, INPUT, AND INTERMEDIATE STORAGE DATA FORMAT While low resolution output data have the limits described above, computations are done in floating point arithmetic. In high resolution Final Storage Input and Intermediate Storage, the numbers are stored and processed in a binary format with a 23 bit binary mantissa and a 6 bit binary exponent. The largest and smallest numbers that can be stored and processed are 9 x 1018 and 1 x 10-19, respectively. The size of the number determines the resolution of the arithmetic. A rough approximation of the resolution is that it is better than 1 in the seventh digit. For example, the resolution of 97,386,924 is better than 10. The resolution of 0.0086731924 is better than 0.000000001. A precise calculation of the resolution of a number may be determined by representing the number as a mantissa between .5 and 1 multiplied by 2 raised to some integer power. The resolution is the product of that power of 2 and 2-24. For example, representing 478 as .9336 * 29, the resolution is 29 * 2-24 = 2-15 = 0.0000305. A description of Campbell Scientific's floating point format may be found in Appendix C. 2.3 DISPLAYING STORED DATA ON KEYBOARD/DISPLAY *7 MODE. The keyboard display (or the computer in Keyboard/Display mode) can be used to examine Data Storage Tables in Final Storage table data. Key *7. The display will show: 07:nn where nn is the number of Data Storage Tables defined. Enter a table number (followed by the "A" key) to view that table. Tables are numbered in the order of the appearance of the Data Storage Table Instruction (84) in the datalogger program. Tables in the *1 program area are numbered first, followed by *2 and those in the *3 subroutines numbered last. The display will then show the first field of the newest record in the table. If the display does not change, the select table has not had any data stored in it yet. When a table is visualized the newest data record is at the bottom and the oldest is at the top. When the table is full and a new record is stored, the records shift up pushing the oldest record off the top and storing the new record at the bottom. The display (or value displayed on the computer) can be thought of as a cursor, which can be moved up and down or right and left through the data. The display shows the field number to the left of the colon and the data value to the right. The keys used to move the display/cursor are summarized in the following table: AD-2-3