Keri Systems SB-293 - Manual (Page 22)

Technical Reference Manual – PXL-250 and SB-293 Keri Systems, Inc.
Page 22 P/N: 01836-004 Revision 5.5
The TWAIN drivers that control communication between many digital cameras
and the badging software are not compatible with the Windows NT 4.0 operating
system. Alternate methods of digital image transfer may be necessary.
6.0 System Cautions
6.1 Earth Ground
You should make a quality earth ground connection to the PXL-250 controller to
ensure the best possible operating conditions for the controller. Without a quality earth
ground connection, the access control system may appear to operate correctly, but will
be extremely susceptible to transients and electromagnetic interference on data and
power lines. An earth ground brings all electrically neutral lines to the earth's surface
potential (essentially to a zero potential) providing three primary benefits to the PXL-
250 controller.
1. An earth ground protects the PXL-250 controller from electrical transients such as
power surges and lightning strikes (also providing a degree of safety for an
operator).
2. An earth ground provides a path to ground for electrical interference minimizing
data and communication problems for the reader data and network communication
lines.
3. Through a feature on the PXL-250 controller the shield for the entire RS-485
network is automatically grounded at one point on the master controller
minimizing communication problems.
Here are some possible sources for an earth ground.
• copper shrouded ground rod
• cold water pipe (must be a metal pipe - not PVC)
• steel building framing member (if the building's frame is embedded in the earth)
• electrical system ground (at the breaker/fuse box)
• telephone system ground
6.2 Electromagnetic Interference
Electromagnetic interference is electromagnetic energy radiated by an electrical
device that may affect the operation of other electrical devices. The PXL-250
controller can be sensitive to electromagnetic interference (EMI), affecting the
controller's performance. To ensure the best operating conditions for the controller,
please review and consider the following suggestions.
6.2.1 Power Supplies
Switching power supplies are known sources of EMI and cannot be used as the VDC
source for the PXL-250 controller or for any proximity reader.