Measurement Computing USB-PDISO8 - Manual (Page 11)

Chapter 3
Functional Details
The USB-PDISO8 provides SPDT relay control and isolated inputs in a plug-and-play package. Screw
terminals provide easy field wiring to the three output lines for each of the eight on-board relays (see Figure 3-3
on page 3-3).
In addition, two terminals are provided for the differential input signals associated with each of the eight
isolated inputs.
Internal components
The USB-PDISO8 has the following internal components, as shown in Figure 3-1.
ƒ
Two (2) USB connectors
ƒ Two (2) external power connectors
ƒ USB LED
ƒ PWR LED
ƒ Two (2) screw terminal banks
PWR LED
USB LED
Digital input screw terminal connectors Relay screw terminal connectors
USB IN
POWER
OUT
POWER IN
USB
OUT
Figure 3-1. USB-PDISO8 components
Direct current (dc) power connector and +9 V power supply
The USB-PDISO8 requires between 6.5 V and 12.5 V of external power. An external power connection is
required to activate the relays and to run tests in InstaCal.
The USB specification allows high power devices to draw up to 725 mA. When all eight relays are energized,
the collective current draw exceeds the maximum allowed for high power USB devices. Therefore, external
power is required.
Use the +9-volt (V) DC power supply cord shipped with the USB-PDISO8 to provide external power to this
connector.
3-1