ADLINK PCI-7258 - Manual (Page 29)

Operation Theory • 21
The PhotoMos relay incorporates the advantages of both a semiconductor
and an electro-mechanical relay. The PhotoMos relay utilizes the MOSFET
as a switch instead of the mechanical contact. Thus the contact resistance
remains stable through the life of the relay. Furthermore, dithering problems
is eliminated.
The PCI-7258 is equipped with 32 PhotoMos relays, which are all form A
type. The load voltage can either be AC or DC. The basic wiring diagram is
shown in figure 5 below.
Figure 6: PhotoMos relay wiring diagram
If an inductive load is connected, the spike voltage may exceed the relay’s
maximum rating. To protect the components, user should add a diode in the
circuit. A typical protection circuit is shown below.
Figure 7: Protection circuit for an Inductive load