1260-132 User Manual
Module Specification 1-4
This is acceptable power dissipation for an individual plug-in
module. If five additional modules are likewise loaded, then the
overall carrier dissipation is approximately 70 W, which is well
within the cooling available in any commercial VXIbus chassis or
the 1256 Switching System. In practice, rarely are more than two
relays are energized simultaneously, and rarely is full rated current
run through every path. In addition, the actual contact resistance is
typically one-half to one-fourth the specified maximum, and
temperatures are normally not at the rated maximum. The power
dissipated by each plug-in should be no more than 15 W if all six
slots are used simultaneously. Consult the Power Dissipation
Section of any other 1260 Adapt-a-Switch card manuals for
additional information.
Most users of a signal-type switch, such as the
1260-132
, switch no
more than a few hundred milliamperes and are able to energize all
relays simultaneously, should they so desire.
Additionally, if fewer plug-in modules are used, more power may be
dissipated by the remaining cards. By using a chassis with high
cooling capacity, such as the Racal Instruments 1261B, almost any
configuration may be realized.
About MTBF
The 1260-132 MTBF is >300,000 hours, calculated in accordance
with MIL-HDBK-217E. Relays are included in this calculation but be
aware that relay life is strongly dependent upon operating
conditions. Factors affecting relay life expectancy are:
1. Switched voltage
2. Switched current
3. Switched power
4. Maximum switching capacity
5. Maximum rated carrying current
6. Load type (resistive, inductive, capacitive)
7. Switching repetition rate
8. Ambient temperature
The most important factor is the maximum switching capacity,
which is an interrelationship of maximum switching power,
maximum switching voltage and maximum switching current.
When a relay operates at a lower percentage of its maximum
switching capacity, its life expectancy is longer. The maximum
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