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SECTION 2 - TECHNICAL DESCRIPTION
40-145 - GUIDANCE ON POWER HANDLING (PXI CHASSIS)
The PXI standard recommends that each slot consumes less than 25 Watts to ensure that the chassis does not
overheat. Some chassis may be capable of handling more than 25W per slot.
For the 40-145 there are three main contributing factors to the power consumption of the module:
Fixed power from the PXI interface and relay controllers
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Relay coil power
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Power loss from the signal being switched due to path resistance.
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Applications vary considerably as to how many relays may be closed and what current each contact carries. Users
should consider how much power the module is likely to dissipate from all sources.
For the 40-145 fitted with SPST normally open relays, Figure 2.1 below provides guidance. It assumes that all
contacts carry the same current and that every path has the resistance value shown on the data sheet. If your
application is likely to load large numbers of contacts with currents over 0.7 Amps you should consult the graph to
find the number of closures we recommend. In most applications this is of no concern since many contacts may be
unused or are relatively lightly loaded.
Figure 2.1 Plot of recommended number of closures of SPST (normally open) relays (vertical)
versus carry current (horizontal, Amps). This assumes a contact resistance of 300mΩ and a
chassis capable of supporting the minimum 25W per slot recommended in the PXI standard.
An example is shown in Figure 2.2 for the 40-145 fitted with SPST normally closed relays where the path resistance
is also assumed to be 300mΩ in a chassis with 25W capacity per slot.
Figure 2.2 Plot of recommended number of closures of SPST (normally closed) relays (vertical)
versus carry current (horizontal, Amps). This assumes an average contact resistance of 300mΩ
and a chassis capable of supporting the minimum 25W per slot recommended in the PXI standard.
Page 2.2
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HIGH DENSITY RELAY MODULES 40-145/146/148
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