Measurement Computing USB-QUAD08 - Manual (Page 27)

USB-QUAD08 User's Guide Functional Details
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Pacing
You can pace synchronous acquisition of counter data by the onboard clock or by an external clock connected
to the
XPCR external pacer input terminal.
Power
The total supply current at the +5V terminal is 480 mA, maximum, including DIO. The total supply current
shared between the +5V terminals is 20 mA, maximum.
You can use the +5V terminal to supply power to external devices or circuitry.
Caution! The +5V terminals are outputs. Do not connect to an external power supply or you may damage
the USB-QUAD08 and possibly the computer.
The maximum total output current that can be drawn from all USB-QUAD08 connections (power, analog, and
digital outputs) is 480 mA. This maximum applies to most personal computers and self-powered USB hubs.
Bus-powered hubs and notebook computers may limit the maximum available output current to 100 mA.
The total current requirements of the USB-QUAD08 is 225 mA, typical. The maximum available excess current
is the difference between the allowed current draw of the computer platform and the total output current
requirement of the device. For an application running on a computer or powered hub, the maximum available
excess current at the +5V screw terminals is calculated as follows:
Maximum excess current = 480 mA – 225 mA = 255 mA
If the current requirement of the device exceeds the current available from the computer, connect to a self-
powered hub or power the computer with an external power adapter.
Encoder power
When operating in Quadrature counter mode, the USB-QUAD08 passes an external supply of up to 50 VDC
(current rated 1.5 A @ 5 VDC) through the
ENC+ IN encoder input power terminal to the ENC+ encoder power
output terminals. Each ENC+ terminal provides power to one encoder.
When operating in normal counter mode, the ENC+ IN and ENC terminals provide no function.
Ground
The ground ( GND ) connections provide a common ground for the digital, counter, and power connections.
Caution! Ensure that the signals are connected such that there is no potential between PC ground and signal
ground.