Do-more H2 Series PLC User Manual, 1st Edition, Rev. F - H2-DM-M
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Chapter 8: Installation and Wiring
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Relay Output Guidelines
Several output modules in the Do-more I/O family feature relay outputs: D2–04TRS,
D2–08TR, D2–12TR, D2–08CDR, F2–08TR and F2–08TRS. Relays are best for the
following applications:
• Loads that require higher currents than the solid-state outputs can deliver
• Cost-sensitive applications
• Some output channels need isolation from other outputs (such as when some loads require different
voltages than other loads)
Some applications in which NOT to use relays:
• Loads that require currents under 10mA
• Loads which must be switched at high speed or heavy duty cycle
Relay outputs in the Do-more output modules are available in two
contact arrangements, shown to the right. The Form A type, or
SPST (single pole, single throw) type, is normally open and is the
simplest to use. The Form C type, or SPDT (single pole, double
throw) type, has a center contact which moves and a stationary
contact on either side. This provides a normally closed contact
and a normally open contact.
Some relay output module’s relays share common terminals,
which connect to the wiper contact in each relay of the bank.
Other relay modules have relays which are completely isolated
from each other. In all cases, the module drives the relay coil
when the corresponding output point is on.
Relay with Form A contacts
Relay with Form C contacts
