ADLINK USB-1903 - Manual (Page 46)

32 Installing the USB-1900 Series Module
If the USB-1900 Series module cannot be detected, the power
provided by the USB port may be insufficient. The USB-1900
Series module is exclusively powered by the USB port and
requires 400 mA @ 5 V.
3.2 Device ID
A rotary control on the rear of the module (as shown) controls
device ID setting and can be set from 1 to 8. The device ID allows
dedicated control of the USB-1900 Series module irrespective of
the connected USB port. When more than one USB module of the
same type is connected, each must be set to a different ID to avoid
conflicts and errors in operation.
Figure 3-2: Device ID Selection Control