Earth Ground And Shielding - Recognition Systems HANDKEY II Manual

general two hours of battery operation can be expected. While operating on
battery backup due to loss of main input power, the battery output voltage is
constantly monitored by internal circuitry. If the battery voltage reaches
approximately 9.5 volts the HandReader automatically shuts down. This is done
to prevent full exhaustion of the battery. A yellow indicator on the top panel
illuminates to indicate that the HandReader is running off of battery power. This
indicator extinguishes when main input power is restored.
Shunt J7 which is located immediately in front of the DIP switches on the main
logic board (see Figure 5-1 on page 25) enables or disables battery operation on
those HandReaders equipped with optional battery backup. If a HandReader
does not have the optional battery backup package installed, J7 is not used. On
HandReaders equipped with the battery backup option, J7 allows service
personnel a mechanism for disabling battery backup operation before removal of
main input power. To fully power down a HandReader equipped with battery
backup, remove or reposition shunt J7 so that the two pins protruding up from
the main logic board are not connected to each other. This effectively opens the
circuit, removing the battery from any internal circuitry. Main input power can
then be removed and the HandReader will fully shut down. Once the HandReader
has fully shut down, shunt J7 may be reinstalled. The design of the power
supply is such that main input power must be reapplied to re-enable the battery
protection mechanism. If shunt J7 is not properly installed, the internal backup
battery will not be charged, and in the event of a main input power loss, the
HandReader will shut down.
The HandReader with the battery backup option uses a 12 volt 800 ma/hour
sealed lead acid battery to provide backup battery power. This battery is located
immediately inside the rear panel of the HandReader and plugs into jack J4 on
the keypad control circuit board located in the top of the chassis.
Earth Ground Recognition Systems recommends that all HandReaders be grounded with a
and Shielding solid, reliable earth ground connection. This connection establishes a common
ground return point used to protect internal semiconductor devices from
ElectroStatic Discharge (ESD) and from external signal line transients. It also
provides a common signal level reference point between externally networked
HandPunchs. Recognition Systems recommends that the earth ground source
be identified by a qualified electrician familiar with electrical codes as well as
wiring and grounding techniques.
This is an extremely important and often overlooked aspect of hard-wired serial
communication systems. If the sending and receiving stations do not agree on
the ground reference for the signal voltages, communication errors or a total
inability to communicate may be observed. If the voltages are very different, it is
even possible to damage the units.
HandKey II Manual
Page 11