Application for the Web-IO Digital:
Web-IO Digital - Supply voltage and input/output circuit
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Web-IO Digital 2 x Input, 2 x Output, Model #57637

In the wiring example shown inputs, outputs and the Web-IO itself are powered from the same source. Alternately the inputs and outputs can be supplied with up to 30V if the Web-IO is supplied separately with max. 24V.
Web-IO Digital 12 x Input, 12 x Output, Model #57630

In the wiring example shown the outputs are supplied separately. This makes output voltages of up to 30V possible. Of course the outputs can instead be supplied by the same source as the Web-IO. The maximum voltage in this case is 24V. The inputs are current sinking and may alternately be driven using active signals between -30 and +30V.
Web-IO Digital 12 x Input, 6 x Relay Type #57634

The inputs of the Web-IO 57634 are technically identical to those of the 57630. The outputs however use potential-free contacts.