VTI Instruments EX1200 Series, Руководство пользователя

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EX1200 Switching Overview 13
322H
S
ECTION
2
S
WITCHING
O
VERVIEW
G
ENERAL
P
URPOSE
S
WITCHING
When selecting switch cards for a test system, the following should be taken into consideration:
 Power Specifications
 Minimum Contact Rating
 Switching Time
 Bandwidth
The relay must be able to accommodate both the voltage, current, and total power that will be
switched and all of these specifications should be checked before making a selection. The
minimum contact rating and switching time specifications are important in systems where relays
will be opened and closed many times throughout the test. The faster the switch performs, the
faster the test will finish. The bandwidth specification indicates the frequencies the switch is able
to switch. Interchannel isolation and crosstalk are also affected by the frequency of the signals
being switched.
P
OWER
S
WITCHING
The EX1200-200x high-power switch cards provide high-power switching in a small form factor.
The EX1200-2001 and the EX1200-2002 are the only switch modules in their class with the
ability to switch up to 16 A. As such, the high-power cards are an ideal solution for applications
such as: ac line power switching, switching of dc or power supplies, controlling or driving relays
for industrial machines (robotics, numerical control machines), automotive engine control, and
solenoid switching. These switch cards also include a front panel interrupt line which will open all
relays in the module to provide safety. They can also be used in the setup phase of a scanlist to
switch power to and from a DUT before reading data into a multiplexer to the DMM.
M
ATRIX
/M
ULTIPLEXER
S
WITCHING
Matrix and multiplexer cards allow the user the ability to combine multiple in the same chassis to
create larger switching systems: For matrix cards, multiple cards can be combined by connecting
either rows or columns of the relay together. For example, by placing six EX1200-4128’s in a
chassis and connecting all four rows of each module to the EX1200 backplane, a 4 x 768 can be
formed is a 1U rack with no external wiring.
To improve bandwidth specifications, it is important to utilize the stub breaking relays that are
incorporated into most matrix and multiplexer cards. These relays typically separate banks of
relays from each other or isolate the switch card from the DMM backplane. By keeping these
relays open, the length a signal must travel, and the amount of resistance it will encounter, can be
reduced, increasing the path’s bandwidth. Examples of these relays are shown in
323H
Figure 2-1.