Measurement Computing WebDAQ 504 User manual

WebDAQ 504
Internet Enabled Vibration/Acoustic Data Logger
User's Guide
October 2017. Rev 1
© Measurement Computing Corporation

2
HM WebDAQ 504
Trademark and Copyright Information
Measurement Computing Corporation, InstaCal, Universal Library, and the Measurement Computing logo are
either trademarks or registered trademarks of Measurement Computing Corporation. Refer to the Copyrights &
Trademarks section on mccdaq.com/legal for more information about Measurement Computing trademarks.
Other product and company names mentioned herein are trademarks or trade names of their respective
companies.
© 2017 Measurement Computing Corporation. All rights reserved. No part of this publication may be
reproduced, stored in a retrieval system, or transmitted, in any form by any means, electronic, mechanical, by
photocopying, recording, or otherwise without the prior written permission of Measurement Computing
Corporation.
Notice
Measurement Computing Corporation does not authorize any Measurement Computing Corporation product for
use in life support systems and/or devices without prior written consent from Measurement Computing
Corporation. Life support devices/systems are devices or systems that, a) are intended for surgical implantation
into the body, or b) support or sustain life and whose failure to perform can be reasonably expected to result in
injury. Measurement Computing Corporation products are not designed with the components required, and are
not subject to the testing required to ensure a level of reliability suitable for the treatment and diagnosis of
people.

3
Table of Contents
Preface
About this User's Guide .......................................................................................................................5
What you will learn from this user's guide .........................................................................................................5
Conventions in this user's guide .........................................................................................................................5
Where to find more information .........................................................................................................................5
Hazardous voltages.............................................................................................................................................5
Hazardous locations.......................................................................................................................................................... 5
Chapter 1
Introducing the WebDAQ 504 ..............................................................................................................6
Powered by Raspberry Pi®..................................................................................................................................6
Integrated operating system and web service .....................................................................................................6
Ethernet interface................................................................................................................................................6
Functional block diagram ...................................................................................................................................7
Unpacking...........................................................................................................................................................7
Chapter 2
Setting up the WebDAQ 504.................................................................................................................8
Connecting to a local area network.....................................................................................................................8
Connecting to a network with DHCP enabled .................................................................................................................. 8
Connecting directly to a PC .............................................................................................................................................. 8
Connecting the external power adapter ..............................................................................................................8
Detecting the device on the network...................................................................................................................9
Accessing the WebDAQ web interface............................................................................................................................. 9
Configuring the WebDAQ for wireless communication ..................................................................................10
Configuring the network router for communication across networks ..............................................................10
Security.............................................................................................................................................................10
Restoring factory default settings .....................................................................................................................11
Chapter 3
Functional Details ...............................................................................................................................12
Front panel components....................................................................................................................................12
Screw terminal .................................................................................................................................................................12
BNC connectors...............................................................................................................................................................12
Rear panel components.....................................................................................................................................13
External power connector ................................................................................................................................................14
Power button....................................................................................................................................................................14
Function button................................................................................................................................................................14
LED status indicators.......................................................................................................................................................14
SD card slot......................................................................................................................................................................15
Factory reset button .........................................................................................................................................................15
Ethernet connector ...........................................................................................................................................................15
Ground connector ............................................................................................................................................................15
USB connectors ...............................................................................................................................................................16
Analog input circuitry.......................................................................................................................................16
Overvoltage protection.....................................................................................................................................................16
AC/DC coupling ..............................................................................................................................................................16
Common-mode bias current.............................................................................................................................................16
Data rates .........................................................................................................................................................................17
Anti-aliasing filters ...........................................................................................................................................17
Passband ..........................................................................................................................................................................17
Stopband ..........................................................................................................................................................................18
Alias-free bandwidth........................................................................................................................................................18

WebDAQ 504 User's Guide
4
Replacing the battery ........................................................................................................................................18
Updating WebDAQ firmware...........................................................................................................................19
Calibrating the hardware...................................................................................................................................19
Chapter 4
Specifications......................................................................................................................................20
Analog input .....................................................................................................................................................20
Digital input/output...........................................................................................................................................21
Network ............................................................................................................................................................22
Ethernet connection .........................................................................................................................................................22
Network interface ............................................................................................................................................................22
Network factory default settings ......................................................................................................................................22
Processor / Memory..........................................................................................................................................23
USB ports .........................................................................................................................................................23
SD memory card slot ........................................................................................................................................23
LED indicators..................................................................................................................................................23
Push buttons......................................................................................................................................................24
Ground connector .............................................................................................................................................24
Power ................................................................................................................................................................25
Mechanical .......................................................................................................................................................25
Shock and vibration ..........................................................................................................................................25
Environmental ..................................................................................................................................................25
Safety voltages..................................................................................................................................................26
Signal connector ...............................................................................................................................................26
Screw terminal .................................................................................................................................................................26
BNC connectors...............................................................................................................................................................26
EU Declaration of Conformity............................................................................................................27

5
Preface
About this User's Guide
What you will learn from this user's guide
This user's guide describes the Measurement Computing WebDAQ 504 data acquisition device and the web
interface, and lists device specifications.
Conventions in this user's guide
For more information
Text presented in a box signifies additional information related to the subject matter.
Caution! Shaded caution statements present information to help you avoid injuring yourself and others,
damaging your hardware, or losing your data.
bold text Bold text is used for the names of objects on a screen, such as buttons, text boxes, and check boxes.
italic text Italic text is used for the names of manuals and help topic titles, and to emphasize a word or phrase.
Where to find more information
Additional information about WebDAQ 504 hardware is available on our website at www.mccdaq.com. You
can also contact Measurement Computing Corporation with specific questions.
WebDAQ web interface: Open the Help page for information about using WebDAQ software; see page 9.
WiFi adapters approved for use with the WebDAQ Series: www.mccdaq.com/pdfs/manuals/wd-wifi.pdf
Knowledgebase: kb.mccdaq.com
Tech support form: www.mccdaq.com/support/support_form.aspx
Email: [email protected]
Phone: [phone] and follow the instructions for reaching Tech Support
For international customers, contact your local distributor. Refer to the International Distributors section on our
website at www.mccdaq.com/International.
Hazardous voltages
Take the following precautions if you connect hazardous voltages to the WebDAQ 504. A hazardous
voltage is a voltage greater than 42.4 Vpk or 60 VDC to earth ground.
Caution! Ensure that hazardous voltage wiring is performed only by qualified personnel adhering to local
electrical standards.
Do not mix hazardous voltage circuits and human-accessible circuits on the same device.
Make sure that devices and circuits connected to the WebDAQ 504 are properly insulated from
human contact.
Hazardous locations
The WebDAQ 504 is not certified for use in hazardous locations.

6
Chapter 1
Introducing the WebDAQ 504
The WebDAQ 504 is part of the WebDAQ Series of Internet enabled data loggers. WebDAQ 504 is a vibration
and acoustic acquisition and logging device that provides the following features:
4 simultaneously sampled analog inputs
24-bit resolution
Data rates up to 51.2 kS/s per channel
AC/DC coupling
IEPE signal conditioning
Anti-aliasing filters
Overvoltage protection
Four bidirectional, isolated DIO
10/100 Ethernet interface
Support for USB WiFi adapters for wireless connectivity
Support for USB mass storage devices and SD cards for data logging or file transfer
Powered by a +9 VDC external supply (included)
WebDAQ Series devices are designed with an integrated operating system and web interface. You
communicate with the device over a network connection using the web interface opened in a web browser.
Mobile support – access the WebDAQ 504 from any device with a web browser, such as a phone or tablet
Remote monitoring and control
Run simple to complex logging operations
Flexible task scheduling
Powered by Raspberry Pi®
The WebDAQ 504 is designed with the Raspberry Pi Compute Module, featuring a quad core processor with
speeds up to 1.2 GHz, 1GB RAM and 4 GB Flash memory.
Integrated operating system and web service
The WebDAQ 504 is a complete data acquisition system containing an embedded operating system and web
server. The operating system resides in internal flash memory, and includes a web service and device driver. All
configuration, acquisition, and data management is performed using the web interface.
Ethernet interface
The WebDAQ 504 has a built-in 10/100 BASE-T auto-negotiation, high-speed communication port. You can
access and configure your WebDAQ 504 from anywhere with access to the network to which it is connected.
A unique MAC address is assigned to each device at the factory. You configure the Ethernet connection settings
through a web interface. The default network name uses the format webdaq-xxxxxx, where xxxxxx are the
lower six digits of the factory-assigned MAC address. You can change this name with the web interface.

WebDAQ 504 User's Guide Introducing the WebDAQ 504
7
Functional block diagram
Device functions are illustrated in the block diagram shown here.
Figure 1. WebDAQ 504 functional block diagram
Unpacking
As with any electronic device, you should take care while handling to avoid damage from static
electricity. Before removing the board from its packaging, ground yourself using a wrist strap or by simply
touching the computer chassis or other grounded object to eliminate any stored static charge.

8
Chapter 2
Setting up the WebDAQ 504
Connecting to a local area network
The WebDAQ requires a TCP/IP connection to a network or the Ethernet port of a computer. A standard
Ethernet cable is shipped with the device.
The WebDAQ IP address type is set by default for DHCP/Link-Local. When connected to a network, the device
first attempts to receive an IP address from a DHCP server. If this fails, a link-local address is used. Use of a
static address requires configuration via the web interface. The IP address identifies the WebDAQ 504 on the
network, and is used to access the web interface.
Connecting to a network with DHCP enabled
Connect one end of the Ethernet cable to the connector on the WebDAQ rear panel, and connect the other end
to a 10Base-T or 100Base-TX compatible Ethernet port, hub, or switch.
Once the device is detected, DHCP assigns an address. A different address may be assigned each time the
hardware is connected to the network.
Connecting directly to a PC
Connect one end of the Ethernet cable to the connector on the WebDAQ rear panel, and connect the other end
directly to the Ethernet port on a PC.
The WebDAQ attempts to communicate with the host PC using 169.254.100.100 – the link-local address stored
on the device. The host PC may accept this address or use a different address. The link-local address is valid
only for communications between the WebDAQ 504 and the host PC to which it is connected.
WiFi support
After successfully configuring a wired connection, you can use the web interface to configure the WebDAQ for
wireless communication. Refer to "Configuring the WebDAQ for wireless communication" on page 10 for more
information.
Connecting the external power adapter
Connect the network cable before connecting to external power
Connecting to the external supply before installing on a network results in the device attempting to auto-
negotiate a network address before one is available.
A 9 volt, 1.67 amp external power adapter is included with each shipment (MCC p/n PS-9V1AEPS230V).
Connect the adapter cord to the power connector labeled EXT PWR on the device rear panel, and plug the
AC adapter into an electrical outlet.
The POWER LED on the rear panel turns yellow as the hardware starts up, and green when it is ready for use.

WebDAQ 504 User's Guide Setting up the WebDAQ 504
9
Detecting the device on the network
WebDAQ uses the "zeroconf" zero-configuration protocol to announce its presence on a local area network.
Zeroconf uses a device name which can be accessed from other computers on the network.
Zero-configuration networking is helpful to find your WebDAQ hardware on the network
The easiest way to add zeroconf support to Windows is to install Bonjour Print Services. Bonjour software is
Apple's implementation of zero-configuration networking, and is readily available as a free download – open a
browser window and search for Bonjour Print Services.
Zeroconf is built into popular applications such as Apple ITunes®and instant messaging software, so your
computer may already support it.
Many Linux systems will have the avahi version of zeroconf installed by default, so it’s likely zeroconf is
available if you’re running Linux.
Accessing the WebDAQ web interface
To access the WebDAQ web interface, open a browser* window and enter http://webdaq-xxxxxx.local, where
xxxxxx is the last 6 digits of the MAC address. This address is on a label at the bottom of the WebDAQ.
If your network is configured for the zeroconf protocol, the WebDAQ web interface opens.
If the web interface does not open or an error is returned, install a device discovery tool such as Bonjour
Print Services. Refer to the note about zero-configuration networking above.
The WebDAQ web interface shown in Figure 2. Note that this figure shows a WebDAQ Schedule that includes
two jobs.
Figure 2. WebDAQ web interface
Use the WebDAQ web interface to configure hardware and acquisition options, schedule and run jobs, and to
view and manage data. The Help window provides details about all components on the web interface.
Once a connection is established and you can communicate to the device, you can change the configuration for
other network scenarios.
* The latest version of Chrome, Firefox, Safari, UC Browser, or Opera recommended. Compatible with IE v11
with the latest Windows Updates installed. Not recommended for use with other IE versions or the Edge
browser.

WebDAQ 504 User's Guide Setting up the WebDAQ 504
10
Configuring the WebDAQ for wireless communication
Once communication is established on a wireless network, you can connect a WiFi adapter to the USB port and
use the web interface to configure the WebDAQ for communication over a wireless network. With the
WebDAQ connected through the wired connection, perform the following procedure.
1. Connect anapproved WiFi adaptorto the USB port on the WebDAQ rear panel.
Alist of WiFi adapters approved for use with WebDAQ Series hardware is available on our website at
www.mccdaq.com/pdfs/manuals/wd-wifi.pdf.
2. Open the WebDAQ web interface in a browser window and gotothe Device window, Network tab.
3. Select WiFi.Once the list ofavailable networks updates, select the wireless network that you want to
connect to, andenter the password, ifany.
If the connection issuccessful, the selected wireless network will show above this list with a checkmark
next to it.
You can click onthe selected network toopen a WiFi Network Settings dialog where you can forget the
current network orconfigure the IP address type (DHCP/Link-Local or Static).
4. Disconnect the Ethernet cable from the LAN connection.
Wait a few seconds, and refresh the browser window.
Changing to a wireless network may require a reboot
If a connection can't be established after changing the network, you may need to reboot the operating system
and restart the WebDAQ using the Power button.
Configuring the network router for communication across networks
To communicate with the WebDAQ over the internet from a computer connected to a different network, you
must change the network configuration of the network router.
Caution! This procedure should only be performed by a network administrator or computer professional.
Incorrect settings can significantly disrupt a network.
In the following procedure, the WebDAQ is installed on the host LAN, the computer is installed on the client
LAN, and it is assumed that you have successfully connected the device to a local network.
1. Determine the IP address of the WebDAQ – open the Device window from the web interface, and note the
IP Address value on the Network Settings tab.
2. Configure your router so that the address determined above is a static address. The procedure for
accomplishing this varies between routers; refer to your router documentation for instructions.
3. Configure the firewall/router to forward an unused port to port 80 on the WebDAQ at the IP address
configured for the device.
Note the static IP address assigned to the router – this is referred to as the WAN address.
4. To access your WebDAQ from a remote location, enter the WAN address followed by the port selected
above preceded by a colon in the web browser.
The format of the address entered in the browser is: 000.000.000.000:00000 (WAN address of router:port
selected for the WebDAQ).
Security
Use the web interface to set the level of access to the website and to change the administrator password.
High: access to the web page requires a password.
Medium: access to the web page is permitted for any user, and data can be read by any user, but changes to
the device configuration or files require a password.
Off: full access is permitted for all users; no password is required.
By default, security access is set to "Off", and the administrator password is set to "admin".

WebDAQ 504 User's Guide Setting up the WebDAQ 504
11
To change the security level or password, open the web interface and go to the Device window, Security tab.
Use the device Reset button to restore security settings to factory default values.
Restoring factory default settings
To restore network configuration and security settings to the factory default values, use a paper clip to press the
CONFIG RESET button. When pressed, the default network and security settings are written to the device and
the WebDAQ is rebooted.
Factory default
Parameter Specification
IP address
192.168.0.101
subnet mask
255.255.255.0
Gateway
192.168.0.1
DHCP setting
DHCP + link-local enabled
Security level
Off
User name
admin (case-sensitive)
Password
admin (case-sensitive; editable)
You can change the network settings, security level, and password with the web interface. The user name
"admin" cannot be changed.

12
Chapter 3
Functional Details
Front panel components
Front panel components are shown in Figure 3.
Figure 3. Front panel
1
Screw terminal
2
BNC connectors
Screw terminal
Connect up to four digital I/O lines (DIO0 to DI03) to the detachable screw terminal. Refer to Figure 4 for signal
locations.
Figure 4. Screw terminal pinout
The digital ground (GND) terminals provide a common ground for the digital bits.
Digital connections
The digital I/O lines are electrically isolated from the analog circuit. Each bit is individually configurable for
input or output, and features Schmitt trigger inputs and open drain outputs. All DIO channels are pulled high to
5 V.
Using the web interface, any digital bit can be configured as a trigger to start or stop an acquisition. Any digital
bit can also be configured to trigger an alarm, and be driven high or low when an alarm occurs.
BNC connectors
Connect up to four analog inputs to the BNC connectors (AI0+/AI0–to AI3+/AI3–). All analog inputs are
simultaneously sampled at rates of up to 51.2 kS/s per channel. A diagram of a typical BNC connector is shown
in Figure 5.
Figure 5. BNC connector, typical
The center pin of the connector (AI+) provides the DC excitation (when enabled) and positive input signal
connection. The shell of the connector (AI–) provides the excitation return path and AC ground reference.

WebDAQ 504 User's Guide Functional Details
13
Use the web interface to individually configure each input for voltage or Integrated Electronic Piezoelectric
(IEPE) sensor measurements. IEPE sensor types include acceleration, sound pressure, velocity, and force.
Voltage channels can be configured for AC or DC coupling. IEPE channels are automatically configured for
AC coupling. An internal excitation source current is automatically enabled for IEPE sensor types.
Analog signal connections
You can connect ground-referenced or floating signal sources to the WebDAQ 504. Use a floating connection
to minimize ground noise.
If you make a ground-referenced connection between the signal source and the WebDAQ 504, make sure the
voltage on the AI– shell is in the common-mode range to ensure proper operation. The AI- shell is protected
against accidental contact with overvoltages within the overvoltage protection range. Refer to the Specifications
chapter on page 20 for more information about operating voltages and overvoltage protection.
Figure 6 shows a diagram for connecting a grounded signal source to the WebDAQ 504.
Figure 6. Connecting a grounded IEPE sensor
Figure 7 shows a diagram for connecting a floating signal source to the WebDAQ 504.
Figure 7. Connecting a floating IEPE sensor
Rear panel components
Rear panel components are shown in Figure 8.
Figure 8. Rear panel
1
External power connector
4
LED status indicators (4)
7
Ethernet connector
2
Power button
5
SD card slot
8
Ground connector with
grounding screw
3 Function button 6 Factory reset button 9 USB connectors

WebDAQ 504 User's Guide Functional Details
14
External power connector
Connect the external AC adapter that shipped with the device to the connector labeled EXT PWR on the rear
panel. The power supply provides 9 VDC, 1.67 A power to the WebDAQ.
If using a different power supply than what was shipped with the hardware, ensure that the supply has a positive
center pin.
Power button
The button labeled POWER turns the WebDAQ device on and off.
Press briefly to turn the device on.
Press for approximately 1 second to begin shutting down the operating system and WebDAQ hardware;
release the button when the POWER LED blinks yellow. The operating system automatically powers off
the WebDAQ device at the end of the shutdown procedure.
If the WebDAQ device stops responding for any reason, you may press the power button and hold it for
approximately 4 seconds to force the device to power off. Any unsaved changes may be lost when
powering down using this method.
Function button
The button labeled FUNC has two functions; it can be used to eject external media or to start/stop an acquisition.
Eject external media (default): Pressing the button unmounts all removable media so they can be safely
removed from the device.
Start or stop an acquisition (requires configuration with the web interface): When configured, pressing
this button starts an acquisition, or stops an acquisition that is currently running.
Use the web interface to safely unmount removable media, when present.
When removable media is plugged into the WebDAQ, the operating system opens it for writing. To safely
remove the media, you must unmount it first.
When a job is configured to log data to external media, pressing FUNC while the job is running will not eject
the media.
The MEDIA LED is steady green when all media is unmounted and safe to remove, and off when all media is
removed.
LED status indicators
The WebDAQ has four LEDs on the rear panel that indicate the status of power and host communications. The
following table defines the LED states during normal operation.
LED states – normal operating mode
Label State Description
1: POWER
Steady yellow
Device is booting up
Steady green
Device boot is successful
Blinking yellow
Device is shutting down
Off
Device is off
2: STATUS
Blinking yellow
Device is configuring hardware
Steady green
Hardware configuration is complete
Flashing green
100 ms on/2s off)
Waiting for a scheduled start condition to be met
Blinking heartbeat
Scheduled start condition is met; waiting for job start condition to be met.
Blinking green
Data is being acquired (job start condition is met)
Off
No error detected.

WebDAQ 504 User's Guide Functional Details
15
Label State Description
3: ERROR
Blinking yellow
Error condition is detected. This LED blinks even when the software is
configured to ignore the error
Error state is cleared when the next schedule starts.
Off
No error detected
4: MEDIA
Blinking yellow
A job is configured to log to external media, but the job hasn't started yet;
pushbutton will not let you eject media
Steady yellow External media is inserted into the SD card slot or USB storage port
Blinking green
Currently logging to an external SD card or USB storage device
Steady green
Media has been made safe for removal using the function button, but has not
been removed
WebDAQ LEDs behave differently when software is being updated on the device. The following table defines
the LED states during a software update.
LED states – software update mode
LED State Description
All LEDs
Solid yellow
Software update is starting
POWER
Blinking yellow
Software update is running
STATUS
Blinking green
Update file is located; device is being updated
Blinking yellow
Update file cannot be located; insert media with update file
ERROR
Blinking green
Update is successful; device will reboot in approximately 5 seconds
Blinking yellow
Update failed; user must retry
Refer to Updating WebDAQ firmware on page 19 for more information about WebDAQ firmware.
SD card slot
The SD slot accepts SD (Secure Digital), SDHC, SDXC, MMC, and TransFlash memory cards. Memory cards
can be ejected using the web interface or the hardware FUNC button, unless the button is configured to
start/stop an acquisition.
When removable media is plugged into the WebDAQ, the operating system opens it for writing. Use the FUNC
button (page 14) or web interface to unmount the SD card before removing.
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
formatted 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 acquisition stops. Before starting a
logging session of this type, reformat the media using a different file system such as NTFS. Refer to
the WebDAQ help FAQ for more information about file formats.
Factory reset button
The recessed button labeled CONFIG RESET restores network and alarm settings to factory default values.
When pressed, the default settings are written to the device and the WebDAQ is rebooted. Refer to page 11 for a
list of the default settings that are restored.
Ethernet connector
The WebDAQ has one 10 Base-T/100 Base-TX, auto-negotiation, high-speed communication port. The port
connector is an RJ-45, eight-position connector. The Ethernet port accepts shielded or unshielded twisted pair
cable. The maximum communication distance without using a repeater is 100 m (328 ft).
Ground connector
The WebDAQ ships with a screw in the connector labeled #6-32. To ground the WebDAQ chassis, attach a ring
lug to a 14 AWG (1.6 mm) wire. Connect the ring lug to the grounding screw on the WebDAQ rear
panel. Attach the other end to a safety ground.

WebDAQ 504 User's Guide Functional Details
16
USB connectors
The two high-speed USB ports can be used for connections to a mass storage device and approved WiFi
adapter. When removable media is plugged into the WebDAQ, the operating system opens it for writing. Use
the FUNC button (page 14) 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 operation. 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
formatted 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 acquisition stops. Before starting a
logging session of this type, reformat the media using a different file system such as NTFS. Refer to
the WebDAQ help FAQ for more information about file formats.
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,
conditioned, and then sampled by a 24-bit Delta-Sigma ADC.
Figure 9. Input Circuitry for One Channel
Overvoltage protection
WebDAQ 504 provides 30 V overvoltage protection 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 automatically
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-limiting diodes when voltage inputs are
connected. 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 floating signal sources. For best accuracy, use a floating connection or use low-impedance leads when
connecting grounded signal sources; refer to the connection diagram shown in Figure 10.

WebDAQ 504 User's Guide Functional Details
17
Figure 10. Measurement Error Introduced by Common-Mode Bias Current
Data rates
The frequency of the master timebase (fm) controls the data rate (fs) of the WebDAQ 504. The internal master
timebase frequency is 13.1072 MHz.
The data rates available on the WebDAQ 504 can be calculated with the following equation:

= ÷ 256
, where nis any integer from 1 to 31.
The data rate must remain within the appropriate data rate range. Using the internal master timebase of
13.1072 MHz results in data rates of 51.2 kS/s, 25.6 kS/s, 17.067 kS/s, and so on, down to 1.652 kS/s,
depending on the value of n.
Anti-aliasing filters
The WebDAQ 504 uses a combination of analog and digital filtering to provide an accurate representation of in-
band signals while rejecting out-of-band signals. The filters discriminate between signals based on the
frequency range, or bandwidth, of the signal. The three important bandwidths to consider are the passband, the
stopband, and the alias-free bandwidth.
The WebDAQ 504 represents signals within the passband, as quantified primarily by passband flatness and
phase nonlinearity. All signals that appear in the alias-free bandwidth are either unaliased signals or signals that
have been filtered by at least the amount of the stopband rejection.
Passband
The signals within the passband have frequency-dependent gain or attenuation. The small amount of variation in
gain with respect to frequency is called the passband flatness. Digital filters adjust the frequency range of the
passband to match the data rate, so the amount of gain or attenuation at a given frequency depends on the data
rate. Figure 11 shows typical passband response for the WebDAQ 504.
Figure 11. Typical passband response

WebDAQ 504 User's Guide Functional Details
18
Figure 12 shows the passband at one data rate.
Figure 12. AC cutoff frequency response
Stopband
The filter significantly attenuates all signals above the stopband frequency. The primary goal of the filter is to
prevent aliasing. Therefore, the stopband frequency scales precisely with the data rate. The stopband rejection is
the minimum amount of attenuation applied by the filter to all signals with frequencies within the stopband.
Alias-free bandwidth
Any signal that appears in the alias-free bandwidth of the WebDAQ 504 is not an aliased artifact of signals at a
higher frequency. The alias-free bandwidth is defined by the ability of the filter to reject frequencies above the
stopband frequency, and it is equal to the data rate minus the stopband frequency.
Replacing the battery
A button cell lithium battery provides the time reference for WebDAQ hardware when the device is powered
off. The average lifespan of the battery is approximately 10 years.
Caution! The discharge of static electricity can damage some electronic components. Before removing the
WebDAQ device from its housing, ground yourself using a wrist strap or touch the computer
chassis or other grounded object to eliminate any stored static charge.
Perform the following procedure to replace the battery.
1. Power down the WebDAQ device and disconnect the power supply.
2. On the rear panel, remove the Ethernet cable, power cable, SD card, and any USB devices.
3. Remove the #6-32 ground screw.
4. Remove the nut and washer from the EXT PWR connector.
5. Remove the two front panel bezel screws and remove the front bezel.
6. Slide out the circuit board with the front panel intact.
7. Remove the battery by sliding it forward toward the slot, and replace with a 3 V button cell battery – type
BR1225, CR1225 or similar.
8. Slide the circuit board back into the enclosure.
9. Attach the front bezel and secure with the two bezel screws removed in step 5.
10. Secure the power connector with the nut and washer removed in step 4, to the power connector, attach the
ground screw, Ethernet and power cables, and any USB devices.
Set the device system clock from the Device window, Device Info tab on the web interface.

WebDAQ 504 User's Guide Functional Details
19
Updating WebDAQ firmware
Device firmware is bundled with the operating system, web server, and documentation in a software update
(*.swu) file. Firmware updates are posted on the Measurement Computing Firmware Updates page and are
available for download.
Use the web interface to install the *.swu update file. Open a browser window and enter http://webdaq-
xxxxxx.local/Help, where xxxxxx is the last 6 digits of the MAC address – refer to the label on the bottom of
the enclosure. Refer to the Updating WebDAQ Firmware help topic or FAQ for instructions.
Calibrating the hardware
The Measurement Computing Manufacturing Test department performs the initial factory calibration. Return
the device to Measurement Computing Corporation when calibration is required. The recommended calibration
interval is one year.

20
Chapter 4
Specifications
All specifications are subject to change without notice.
Typical for 0 °C to 50 °C unless otherwise specified.
Analog input
Table 1. Analog input specifications
Parameter Condition Specification
Number of channels
4 analog input channels
ADC resolution
24 bits
Type of ADC
Delta-Sigma (with analog prefiltering)
Sampling mode
Simultaneous
Internal master timebase
(fM)
Frequency
13.1072 MHz
Accuracy
±50 ppm max
Data rate range (fs)
1.652 kS/s min
51.2 kS/s max
Data rates (fs) (fM÷ 256)/n, where n is any integer from 1 to 31
Input coupling
AC/DC; software-selectable
AC cutoff frequency
–3 dB
0.5 Hz
–0.1 dB
4.6 Hz max
Input range
±5 V
AC voltage full-scale range
±5 Vpk min
±5.1 Vpk typ
±5.2 Vpk max
Common-mode voltage
range
AI– to earth ground ±2 V max
IEPE excitation current
Automatically enabled for IEPE
channel types
2.0 mA min
2.1 mA typ
Power-on glitch
90 μA for 10 μs
IEPE compliance voltage
(Note 1) 19 V max
Overvoltage protection,
with respect to chassis
ground
Signal source connected to AI+
and AI–
±30 V
Low-impedance source
connected to AI+ and AI– –6 V to 30 V
Input delay
(40 + 5/512)/fs+ 2.6 μs
Gain drift
0.14 mdB/°C (16 ppm/°C) typ
0.45 mdB/°C (52 ppm/°C) max
Offset drift
19.2 μV/°C typ
118 μV/°C max
Channel-to-channel
matching
Phase (f
in
in kHz)
f
in
× 0.045° + 0.04 max
Gain
0.01 dB typ
0.04 dB max
Passband
Frequency
0.45 × f
s
Flatness (f
s
= 51.2 kS/s)
±40 mdB (pk-to-pk max)
Phase nonlinearity
f
s
= 51.2 kS/s
±0.45° max
Stopband
Frequency
0.55 × f
s
Rejection
100 dB
Alias-free bandwidth
0.45 × fs
Oversample rate
64 × f
s