Measurement Computing USB-1608HS-2AO - Manual (Page 18)

USB-1608HS-2AO User's Guide Functional Details
18
Wire- and cable-type interconnects have some amount of associated series resistance. To calculate the total
series resistance, multiply the overall length by the manufacturer's specified resistance per unit length (Ω). If the
series resistance becomes large enough, a voltage drop error occurs along the wire when supplying current to
the load resistance. The remote sensing feature compensates for the voltage drop error that occurs along the
wire.
Connecting the USB-1608HS-2AO when using the remote sensing feature
To connect the USB-1608HS-2AO for remote sensing, connect two separate output wires—one from the
VDACn_F (force) output terminal, and one from the VDACn_S (sense) input terminal—to the high side or
positive input terminal of the field device (load). The "n" in the terminal name refers to the number of the
analog output terminal (0 or 1).
For best results, these two wires should have identical length and gauge. The use of a twisted pair is highly
recommended.
In this configuration, the sense wire detects the voltage at the end of the force wire, and compensates for the I*R
loss along the wire due to the wire resistance.
R
load
should not exceed the specified 1000 Ω, and the R
series
should not exceed its specified limit of 75 Ω.
V
compliance
= ((R
load
+ R
series
) * AOUT)/R
load
Connecting the USB-1608HS-2AO when not using the remote sensing feature
If you are not using the remote sensing feature, connect a single output wire or cable from the VDACn_F
(force) output terminal(s) to the load, and leave the VDACn_S (sense) terminals unconnected.
The voltage output range for each channel is ±10 V. The current output is a maximum of ±10 mA per channel.
Analog ground terminals
The 10 analog ground (AGND) connections provide a common ground for all analog input channels, output
channels, and the analog trigger (TRIG_IN).
Refer to the pinout diagram on page 14 for the location of the AGND terminal pins.
Digital input terminals (DI0 to DI7) and digital output terminals (DO0 to DO7)
You can connect up to eight digital input lines to screw terminals DI0 through DI7.
You can connect up to eight digital output lines to screw terminals DO0 to DO7.
Refer to the pinout diagram on page 14 for the location of these pins.
(75 max)
R
Series
VDAC_F
(
n
Force)
VDAC_S
(
n
Sense)
R
(1000 max)
Load