Campbell NL115 Manual download pdf (Page 35)

Section 5. Data Retrieval

Data stored on CF cards can be retrieved through a communication link to the datalogger

or by removing the card and carrying it to a computer.

5.1 Via a Communication Link

Data can be transferred to a computer via a communications link using one of

Campbell Scientific’s datalogger support software packages (e.g., PC200,

PC400, LoggerNet). There is no need to distinguish whether the data is to be

collected from the CPU memory or a CF card. The software package will look

for data in the CPU memory and then the CF card.

The datalogger manages data on a CF card as final storage table data,

accessing the card as needed to fill data collection requests initiated with the

Collect button in datalogger support software. If desired, binary data can be

collected using the File Control utility in datalogger support software. Before

collecting data this way, stop the datalogger program to ensure data are not

written to the CF card while data are retrieved. Otherwise, data corruption and

confusion will result.

5.1.1 Fast Storage/Data Collection Constraints

When LoggerNet collects data from ring tables that have filled, there is the

possibility of missing records due to the collection process. LoggerNet uses a

“round-robin” collection algorithm that collects data from multiple tables in

small blocks as it sequences around to all of the tables. Collection starts at the

oldest data for each table. When a ring table has filled, the oldest data is being

overwritten by current data.

With filled ring tables, as collection begins LoggerNet queries the datalogger

for the oldest data starting with the first table. When this data block is returned

LoggerNet goes to the next table and so on until all of the tables are initially

collected. By the time LoggerNet makes the second pass requesting more data

from the tables, the possibility exists that some of that data may have been

overwritten, depending on how fast the datalogger is storing data (i.e,, data

storage rate, number of table values, and number of tables).

Normally, LoggerNet gets ahead of the storing datalogger and the remaining

data is collected without gaps; however, if the datalogger is storing data fast

enough, it is possible to get into an always-behind-scenario, where LoggerNet

never catches up and the datalogger repeatedly overwrites uncollected data.

The possibility of missing records is greater when collecting data via IP. This

is due to the high demand of IP on processor time. The risk is greatest with a

CR1000 datalogger using IP, because of its slower processor speed relative to

the CR3000.

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Campbell NL115 Manual Page 35