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Usage Information
Using Relay Outputs
This section describes how to obtain the safest and most reliable use of
the PDISO-8 with certain applications.
The relay output contacts are rated for a maximum of 3A at 28VDC or
125VAC (resistive). You should reduce these ratings for inductive loads. If
switching currents are approaching maximum ratings, add a snubber
network to minimize arcing and extend contact life. Figure 4-5 shows a
snubber network across a relay contact.
Source
Voltage
R
Snubber
Figure 4-5. Adding a Snubber Network Across Relay Contacts
Five outputs are organized as Form C (change over) contacts. The
remaining three outputs are plain Form A (normally open) contacts.
Although high voltage can be switched directly by the PDISO-8 installed
in your computer, you are urged to do high-voltage switching only with a
complete understanding of the risks and hazards involved. These risks
include electric shock from accidental contact with the board inside the
computer, and possible damage to the computer through inadvertent
shorts between live circuitry to the system board (caused by foreign
objects or screw drivers, and so on). If you cannot be absolutely certain of
avoiding these situations, you are safer limiting the relay outputs of the
PDISO-8 to switching control voltage circuits (5 to 24V slave relays or
contactors for switching line power circuits).
Relay
Load
C
Snubber Values:
I 2
----- - µF
C
=
10
Where
I = Load Current
E = Source Voltage
4-5
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