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modbus RS-485 Modbus Controller - Modbus Master Controller
5 Year Warranty

Monitor up to 32 modbus devices/sensors as well as a 1-Wire Bus for Temperature and Humidity Monitoring



Up to 32 Modbus RS-485 devices

Up to 16 temp/humidity sensors


Email Alerts



BASIC Interpreter








In Stock


Modbus Master Controller

Web Enabled

Up to 32 modbus RS-485 sensors.

Cellular capable

Monitor remote locations or bypass local networks. Cloud included.

On-device task builder logic

Easily create custom on-device logic, no scripting necessary.

Dual-SIM technology

Intelligent SIM card connects to strongest available signal.


Share real-time sensor states with other ControlByWeb devices.

Logging and Graphing

Log and graph sensor states over time. On-device or on the cloud.

Email/Text Alerts

Customizable email/text alerts based on sensor states.

Modbus Master RS-485 contoller Cloud gateway device

Ideal for connecting incompatible ControlByWeb devices to the cloud.

Industrial Internet of Things (IIoT)

IIoT applications require remote communications, efficient wiring, and reliable performance. Our X-404 Modbus Master RS-485 Controller facilitates all three with our cellular module, multi-drop modbus wiring, and rock-solid performance. Our new cloud makes remote monitoring and control in IIoT applications easier than ever with simplified setup and deployment.

Fluid Level Monitoring

Use the X-404 modbus controller to monitor fluid levels through the module's Modbus protocol.

Remote Monitoring RS-485 Sensors

The X-404 modbus control module functions as a web-based, cloud compatible Modbus master controller and monitor for third-party RS-485 modbus sensors and devices. In this illustration, the X-404 is connected to the MPX Float Sensor, as well as the MND Modbus Display for local level monitoring. The X-404 can also be connected to pressure sensors, like the PT-500 for other level monitoring options. Reap the benefits of modbus integration with easy setup, reliability, and daisy-chaining capabilities.


The X-404 module is designed to automatically program modbus sensors when connected, without using an external power supply or separate programming module. All ControlByWeb devices, with their various combinations of inputs and outputs, can function as a Modbus/TCP slave device controlled by the X-404 controller.

Email/Text Alerts

Configure the X-404 to send email/text alerts when the level reaches user-defined high/low paramaters. Enable logging to record the history of sensor states.

X-404 modbus Master RS-485 Controller connects to many different sensors

The X-404 modbus controller monitoring fluid levels through Modbus

Cell Modem Optional

Keep all the same functionality of the X-404, but with cellular connectivity on the X-404C. Easily monitor remote locations that lack Internet infrastructure, or protect access to your devices with a connectivity failover. The ControlByWeb Cloud access is included with a cellular data plan. Learn more about the ControlByWeb Cloud.

Flexible Communications


The X-404 connects to IP networks and control systems using TCP/IP communication over Ethernet. This is ideal for local monitoring and can also be used for remote monitoring by visiting the device IP address on the Internet through port forwarding. Port forwarding also allows peer-to-peer communication between devices.


Remote locations without an Internet connection are now easier to monitor with the cell-enabled X-404C model. Our cellular data plans include a ControlByWeb Cloud subscription to streamline access to the device setup, task builder, and control pages. The cellular model connects to the strongest available network. Check coverage map.


The ControlByWeb Cloud simplifies monitoring, control, and data logging. It provides access to your controller, but keeps logic on the device so you are not dependent on network connectivity. Get the best of both worlds with our reliable platform. A cloud subscription is included with your X-404C cellular data plan at no additional cost.

X-404C Modbus Controller & The ControlByWeb Cloud

The new X-404C version adds a cellular modem and native compatibility with the ControlByWeb Cloud. The cloud subscription and cellular data work together and are required to access the device setup and control pages. The subscription (device seat) is included when you purchase an annual data plan. This powerful pair makes remote monitoring and control simpler and easier than ever.

With the cloud, you can manage multiple locations and many devices with a single login. Parent-child account hierarchy makes data organization easy for end users and customer management a breeze for resellers and systems integrators.

The ControlByWeb Cloud is compatible with all our 400 Series (X-400, X-405, X-410, etc.) and Wi-Fi modules. To connect with the cloud, an Internet connection is required.

  • Easier Access
  • Data-Logging
  • Logic Stored on Device, Not the Cloud
  • Security Layers
  • Single Password Authentication
  • Parent-Child Accounts
  • Connect Non-Compatible Devices
  • Connect Unlimited End Points


  • Connect up to 32 modbus devices/sensors
  • 1-Wire Bus for up to 16 sensors (temperature, humidity, etc.)
  • Optional cellular module for remote locations or cellular failover
  • Monitor,log, and control up to 32 remote modules, or up to 64 I/O
  • ControlByWeb cloud compatibility
  • User Permissions: Admin, Manager, User
  • Tasks
    • 50 Scheduled
    • 50 Conditional
    • 20 Override Schedules
  • Send email alerts based on user-defined conditions (supports encrypted email servers, such as Gmail)
  • Real-Time Clock with NTP server synchronization
  • Automatic daylight savings and leap year adjustment
  • No software required
  • Customizable web-based Control Page
  • BASIC script support for advanced flexibility
  • Configurable logging
  • Graphing (logged data)
  • HTTPS/TLS encrypted
  • Static or DHCP IP address configuration
  • Modbus, SNMP, Remote Service, IP Filtering
  • Field updatable
  • Rugged DIN-Rail/wall-mountable enclosure
CE listed RoHS compliant Made in the USA

X-404 Part Numbers (Differences highlighted in green)

X-404-I Networking: Ethernet
Temp: Up to 16 sensors.
Modbus: Up to 32 devices/sensors
Task builder, email daily log file, add 64 I/O on up to 32 Remote I/O Modules 9-28 VDC
X-404C-I-CA Networking: Ethernet and/or Cellular
Temp: Up to 16 sensors.
Modbus: Up to 32 devices/sensors
All X-404 features plus cellular modem. 9-28 VDC
X-404 Modbus Master RS-485 Controller X-404 Modbus Controller
Starting at: $399.99 In stock

Buy Now

More Information:


Where to Buy

Click "Buy Online" to view part numbers and pricing. X-404 is available in the USA and internationally, and can be purchased either from us or an Authorized Distributor.

Warning: May contain chemicals, including Nickel (metallic), known to the State of California to cause cancer and reproductive harm. -



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