Campbell Scientific CR6 CR6 Measurement and Control System - Page 209
TableFile, Status, Retrieve, Collect, Custom Collect, TableName.FieldName
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Section 7. Installation memory is pre-allocated). When using TableFile() with Option 64, program compile times can be lessened by reducing the number of records or data-output interval that will be included in each file. For example, if the maximum file size specified is 2 GB, the datalogger must scan through and pre-allocate 2 GB of CF card memory. However, if smaller files are specified, then compile times are reduced because the datalogger is only required to scan through enough memory to pre-allocate memory for the smaller file. Q: Why does a freshly formatted card cause long compile times? A: Program compile times take longer with freshly formatted cards because the cards use a FAT32 system (File Allocation Table with 32 table element bits) to be compatible with PCs. To avoid long compile times on a freshly formatted card, format the card on a PC, then copy a small file to the card, and then delete the file (while still in the PC). Copying the file to the freshly formatted card forces the PC to update the info sector. The PC is much faster than the datalogger at updating the info sector. FAT32 uses an "info sector" to store the free cluster information. This info sector prevents the need to repeatedly traverse the FAT for the bytes free information. After a card is formatted by a PC, the info sector is not automatically updated. Therefore, when the datalogger boots up, it must determine the bytes available on the card prior to loading the Status table. Traversing the entire FAT of a 16 GB card can take up to 30 minutes or more. However, subsequent compile times are much shorter because the info sector is used to update the bytes free information. Q: Which memory card should I use? A: Campbell Scientific recommends and supports only the use of xyz brand micro SD cards. These cards are industrial-grade and have passed Campbell Scientific hardware testing. Following are listed advantages these cards have over less expensive commercial-grade cards: • less susceptible to failure and data loss • match the datalogger operating temperature range • faster read/write times • better vibration and shock resistance • longer life spans (more read/write cycles) Q: Can closed files be retrieved remotely? A: Yes. Closed files can be retrieved using the Retrieve function in the datalogger support software File Control (p. 496) utility, FTP, HTTP, or e-mail. Although open files will appear in the CRD: drive directory, do not attempt to retrieve open files. Doing so may corrupt the file and result in data loss. Smaller files typically transmit more quickly and more reliably than large files. Q: Can data be accessed? A: Yes. Data in the open or most recent file can be collected using the Collect or Custom Collect utilities in LoggerNet, PC400, or RTDAQ. Data can also be viewed using datalogger support software or accessed through the datalogger using data table access syntax such as TableName.FieldName (see CRBasic Editor Help). Once a file is closed, data can be accessed only by first retrieving 209
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