Instructions

UM-0085-B09 DT80 Range User Manual Page 96
RG
• logging preparation time – the time taken to generate a data record to be logged
• file system time – the time taken to physically write the data to the internal flash disk or external USB device.
The first three of these depend on the job and the logger settings. We can largely eliminate them by defining a job
consisting only of CVs, and switching off real time data returns (
/r).
As discussed above, there is a storage overhead associated with each data record; hence 20 records each with one
channel will require more space than one record with 20 channels. The same goes for time – there is a fixed time
overhead in preparing a data record, plus a variable time which depends on the number of channels.
The following table list some typical logging rates:
Schedule
Description
Logging rate
/r RA("B:") 1CV
log one CV to internal memory 55 records/s
/r RA("B:") 1..20CV
log 20 CVs to internal memory
40 records/s
/r RA("A:") 1CV
log one CV to 512M USB device 4 records/s
/r RA("A:") 1..20CV
log 20 CVs to 512M USB device
3 records/s
There may be some variation in performance depending on the brand and capacity of the USB device, but in general
logging to USB will be around an order of magnitude slower than logging to the internal flash memory.
Logging Options
Various data logging parameters can be changed by means of schedule options. These options are inserted in a
schedule definition just before the schedule trigger. See Schedule Options (P49) for details.
Schedule options can be used to specify:
• the logging destination. Using the
"A:" schedule option it is possible to configure a schedule to data directly to
a USB memory device. In this case the store file will be placed in the
A:\SNserial-num\JOBS\jobname\sched folder.
• the space allocated for data. This can be specified in bytes, records, or (for time-based schedules) as a time
period ("I want to store 30 days of data")
• the space allocated for alarms
• whether new data/alarm records are permitted to overwrite old records (
OV) or whether logging should stop
when the store file is full (
NOV).
For example, the following schedule definition:
RA(DATA:30D)1M 1V 2V LOGONA
will allocate a store file with space for 43,200 data records (30x24x60). No space is allocated for alarms because no
alarms are defined in this schedule.
Note1: When determining how much space to allocate for data storage, it is important to ensure that adequate free space
remains on the 128MB or 2GB internal flash memory. If you choose to retrieve logged data by either:
• unloading it to an FTP server, or
• unloading in DBD format via the web interface (dEX)
then there must be sufficient space available on the internal drive to create a temporary file prior to sending to the server. The
space required will depend on the amount of data being unloaded. If you unload the entire contents of a 10MB storefile to FTP
in DBD format then you will need 10MB of free space for the temporary file. If you unload in CSV format then the space required
will be of the order of 10MB, but may be less or more depending on the data values.
As a rule of thumb, if you plan to use one of the above unload methods then you should generally size your storefiles so that
they occupy no more than 50% of the total space on the DT80 internal drive.
Note2: It is normally better to always log data to the internal file system. Logging directly to a USB device is possible, but is subject to
the following caveats:
• The logging performance is significantly slower than for the internal drive.
• There is the potential for data corruption if the USB device is removed during a write operation. Be sure to always halt
logging and use the
REMOVEMEDIA command (see Using a USB Memory Device (P115)) to shut down the device
prior to removing it.
• The DT80's USB socket is designed for easy access, and will not necessarily retain a USB device securely over a long
period, particularly if the DT80 is wall mounted or subject to vibration.
Factors Which May Prevent Logging
When a job is loaded onto the DT80, the logger will attempt to create all required store files. If this is not possible then
the job will not be loaded.
Insufficient Space to Create Store File
When a job is entered, the DT80 attempts to create a store file of the required size. If, however, there is insufficient free
space on the selected logging drive (or it is not present at all) then an error will be reported and the job will not be loaded.