Measurement Computing SWITCH AND SENSE 8/8 - Manual (Page 12)

3-1
Chapter 3
Functional Details
The Switch & Sense 8/8 expands the capabilities of desktop personal computers by providing 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 3-2 on page 3-2).
In addition, two terminals are provided for the differential input signals associated with each of the eight
isolated inputs.
External components
The Switch & Sense 8/8 has the following external components, as shown in Figure 3-1.
! Direct current (dc) power connector
! External power LED
! Status LED
! USB connector /cable
STATUS
LED
EXTERNAL POWER
LED
USB connector/cable
Direct Current
power connection
(7.5 to 20 V)
Figure 3-1. Switch & Sense 8/8 external components (rear view)
Direct current (dc) power connector and +9 V power supply
The Switch & Sense 8/8 requires between +7.5 V and +20 V of external power. Your computer can configure
the Switch & Sense 8/8 without external power. However, 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 500 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 Switch & Sense 8/8 to provide external power to
this connector.