HP 82479A Owner's Manual page 121

Defining A Data Logging Problem
system. Frequent data transmission on the loop can drain the batteries in some peripherals faster than the
trickle charge rate.
For an extended data acquisition run, printer and/or disc drive power consumption may be the limiting
factor. Both the HP 222 5B ThinkJet Printer and the HP 9114A Disc Drive use more power in continuous
operation than the a.c. trickle charger can provide.
Typically, the HP 2225B ThinkJet Printer will run continuously for two to three hours on a full battery
charge. The a.c. trickle charger will extend this period only slightly.
The HP 9114A Disc Drive can operate intermittently for about six hours assuming the following
conditions:
1) The battery starts with a full charge
2) The loop is powered down between disc accesses.
3) The period between disc accesses is five minutes (minimum).
Depending on how much data is written to the disc at each access, an a.c. trickle charger may allow the
system to run for longer periods of time.
If you need to operate a data acquisition system where there is no a.c. power, you can use the HP 3421A
Option 214 12-Volt Power Assembly to extend the period of operation. The option 214 assembly can be
used to power the HP 3421A Data Acquisition/Control Unit from an external battery, and to trickle
charge peripherals such as the HP 9114A Disc Drive and the HP 2225B ThinkJet Printer.
As the interval between loop activity periods gets longer, the overall duration of an experiment can
increase, especially if a.c. trickle chargers or the option 214 are able to restore some or all of the lost
power to the batteries. The LII5 program uses three techniques to reduce the overall system power
consumption requirements:
o Loop power down: The event scheduler in the L.[1z program may, as an option, issue a loop power
down command between clusters of scanning activity. If multiple groups are scheduled to scan at
the same time, they will run in order with no intermediate loop power down. Note that the
digital output channels on the option 050 digital cards are not latched, so they will clear when the
HP 3421A receives a loop power down command.
o Internal data storage: If the data being acquired will fit in a sufficiently small file, the disc drive
does not need to be in the system at all. The HP-71 can store the data file in RAM.
o Buffered data storage: If the data file will not fit in the available RAM, a disc drive must be
used. Rather than write each scan to the disc as it is acquired, a file called ElLIFFEF is created
in HP-71 memory. All group scans are written to this file until there is no memory left in the
HP-71. At that time, all scans are written out to the disc. This technique greatly increases the
interval between actual disc writing activity, depending on the amount of available memory in
the HP-71.
You can also conserve power by connecting the disc drive to a second loop using the HP 82402A Dual
HP-IL Adapter and two HP 82401 A HP-IL Interfaces. Connect the HP 3421A and any other devices
required for measurement on loop 1. Connect the disc drive on loop 2. With this configuration the disc
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