14
PowerLab Owner’s Guide
must be no more than 5 metres (16 feet) in length. Thus, no device can
be more than 30 metres (98 feet) from the computer.
USB lets one plug in and remove devices while the computer is on. It
re-enumerates (provides addresses for) devices as they are connected
and disconnected, rather than requiring fixed ID numbers.
USB still has some restrictions. Since all the devices on a USB tree
have a common communication pathway, if you have many devices
with a lot of information to transfer, they compete for capacity
(bandwidth). Using a video camera and a scanner at the same time as
a PowerLab may limit the sampling rates considerably (in Chart) or
increase delay times between sweeps (in Scope).
USB has two sorts of cables, which it should not be possible to
interchange. Low-speed cables are cheaper, and suitable for mice and
so on. They are either captive (one end is permanently fixed to the
device) or use a custom connection, not a standard USB one. All
detachable USB cables are high speed, with fully shielded twisted-
pair cables, and standard USB connections: a narrow rectangular A
plug at one end and a squarer B plug with a bevelled top at the other.
All devices that can act as hubs have high-speed connections. The
PowerLab needs a high-speed connection, and is provided with a
suitable cable.
Connecting the PowerLab Using USB
Use the USB cable supplied with your PowerLab to connect the USB
port on its back panel to the USB port on the computer, or to an active
USB hub connected to the computer. USB ports and cables should be
marked with a trident-like icon (some might have the letters ‘USB’
instead). USB cables are directional, and can only be connected one
way: the narrow rectangular A plug connects to a hub (including the
computer), and the squarer B plug with the bevelled top connects to a
USB device, such as the PowerLab.
Connecting Macintosh or Windows computers should be much the
same in this case: just look for the icons. If the connection is to a USB
card installed in the computer, there might not be any icons on the
card. The narrow rectangular sockets for the USB A plug are
distinctive, though. Any USB icons on the plugs should be on top.
Summary of Contents for PowerLab 2/20
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