USB connectors
The two high-speed USB ports can be used for connec ons to a mass storage device and approved WiFi
adapter.
When removable media is plugged into the WebDAQ, the opera ng system opens it for wri ng. Use the FUNC
bu on or web interface to unmount the USB device before removing.
Use a self-powered hub when external media requires higher current
USB-powered hard drives may use an excessive amount of current during opera on. The WebDAQ
device could shut down or experience other errors if the power requirements of a connected device
exceed the power available. Use a self-powered hub if the current requirement of external media
exceeds 500 mA.
We recommend that you connect USB-powered hard drives before powering up the WebDAQ.
Acquiring data at high speeds can generate large file sizes
If you expect to acquire a large amount of data to a single file when logging to external media, do not
use media forma ed with the FAT32 file system. FAT32 is limited to a 4 GB maximum file size. If the log
file on FAT32 media grows beyond that size, a "File too large" error is returned and the acquisi on stops.
Before star ng a logging session of this type, reformat the media using a different file system such as
NTFS. Refer to the Frequently Asked Ques ons help topic for more informa on about file systems.
Analog input circuitry
The analog input channels are referenced to chassis ground through a 50 Ω resistor. To minimize ground noise,
make sure the chassis ground is connected to earth ground. The input signal on each channel is buffered,
condi oned, and then sampled by a 24-bit Delta-Sigma ADC.
Figure 9. Input Circuitry for One Channel
Overvoltage protec on
WebDAQ 504 provides 30 V overvoltage protec on for each channel.
AC/DC coupling
Use the web interface to configure voltage channels for AC or DC coupling. Configure for DC if the signal has no
offset voltage or if the DC content of the acquired signal is not important.
AC coupling is automa cally enabled for IEPE channels to remove any DC offset from the measurement.
Common-mode bias current
The WebDAQ 504 uses common-mode bias current to bias the current-limi ng diodes when IEPE current is
turned off. When the WebDAQ 504 is using grounded signal sources, the current causes an error that is
dependent on the AI– lead impedance, and is approximately 50 ppm of range and 15 ppm of reading per Ω of
AI– impedance. The common-mode bias current causes an error only with grounded sources and is not an issue
with floa ng signal sources. For best accuracy, use a floa ng connec on or use low-impedance leads when
connec ng grounded signal sources; refer to the connec on diagram shown in Figure 10.
WebDAQ 504 User's Guide
page 14
