The inputs and outputs of a card are controlled by software.
If a relay is adressed a contact is either opened or closed. By that it is responsible to take into account, that the external current is not chosen to high, because in that case the switching contacts of the relay are overloaded. Every relay has two own connections, so that the switching between currents with different potentials and also the switching of alteranting voltage is possible.
In contrast to a relay, the controlling signal is light. Opto couplers can only switch DC circuits and record DC processes (opto inputs and outputs), but their special merits are high switching speed and a relatively wide voltage range (see technical data). All opto couplers have one common earthing. TTL conductions work bidirectional, they are inputs and outputs. Therefore, they can both record data and control external devices.
Relay cards are very useful for the power switching. They are very flexible by choosing the used voltages and can also be used for currents higher than 1 A ore more. To switch surrent circuits on or off, which work with a alternating voltage of 25 V it is recommandable to use a 230 V card. With this card the 230 V are leaded direct to the PC. If this is not the result you can alternatively use a normal relay-, opto- coupler- or TTL- card, if you connect an extern relay with the corresponding current supply.
Opto coupler cards are used if a galvanical separation of circuits is needed or sensible (for example to avoid trouble when transmitting data over long dinstances). Without special drivers, they can only be used for low currents. The opto coupler card which records external switching processes fastest and most precisely is best suited.
Relays are used as switches.
If a relay is connected by our cards, the switching contact is either opened or closed, so that a connected current circuit (with external power supply) is opened or closed. Please note, that the extern current must not be to big, otherwise the switching contacts of the relay is overloaded. There are two different types of relays. The switch-on relays close and the switch-over relays open or close one switching circuits each.
Switches depending on current which realize by their design a galvanical separation to the computer. Opto couplers switch very fast, but are restricted in the usability by a voltage range of 30 V direct current.
'Galvanically separated' means that the separated components have no electrical conductions to each other. A galvanical separation to the computer guarantees that voltages of the module cannot break into the computer.
All opto couplers are combined in 8 part groups. That means that 8 opto couplers have one common earthing. On reason for that is to avoid unnecessary sources of interference.