R4IVB02: 2-Channel 4–20 mA Analog Input Module with RS485 Modbus RTU

R4IVB02 is a compact, two-channel analog input acquisition module designed for industrial sensor monitoring, process measurement, and remote data collection. Featuring a 12-bit analog-to-digital converter (ADC), an RS485 interface, and Modbus RTU communication, it enables compatible controllers and computers to collect analog measurements through a standard serial network.

The R4IVB02 is available in several hardware configurations, including voltage-input and current-input versions, with different power supply requirements. The current-input version is particularly suitable for industrial transmitters using 0–20 mA or 4–20 mA signals, while the voltage-input version supports compatible 0–5 V and 0–10 V signals.

Unlike larger industrial I/O systems, the R4IVB02 uses a compact PCB and screw-terminal connections, making it a practical choice for OEM equipment, embedded monitoring systems, and cost-sensitive automation projects.

Its documented support in the GitHub project ha-modbus-manager also provides a useful starting point for developers who want to integrate the current-input version into Home Assistant.

2. Key Features

  • Two analog input channels: Acquire two independent voltage or current signals, depending on the selected hardware version.

  • 4–20 mA current measurement: Suitable for compatible industrial transmitters and process sensors.

  • 0–20 mA measurement: Supports compatible current-output devices within the specified input range.

  • Voltage-input options: Available in 0–5 V and 0–10 V configurations.

  • 12-bit ADC: Converts analog signals into digital measurement data.

  • RS485 communication: Supports serial networking for distributed monitoring and automation.

  • Modbus RTU protocol: Compatible with supported PLCs, computers, industrial gateways, and embedded controllers.

  • Flexible power supply: Available in 4–5.5 V DC and 6–25 V DC versions.

  • Configurable communication: Supports Modbus read functions 03 and 04 and write functions 06 and 16, as documented by the manufacturer.

  • Calibration support: The manufacturer recommends calibration when measurement error exceeds its stated threshold.

  • Screw-terminal wiring: Simplifies field connections compared with small pin-header-only modules.

  • Compact design: Approximately 41.5 × 20 × 6 mm.

  • Multi-device networking: Supports up to 247 devices in Modbus command mode, subject to addressing and electrical network requirements.

3. Technical Specifications

Parameter Specification
Model R4IVB02
Module type Two-channel analog input acquisition
Number of channels 2
Current-input range 0–21 mA
Supported current signals 0–20 mA / 4–20 mA
Voltage-input versions 0–5 V / 0–10 V
ADC resolution 12-bit
Manufacturer-stated measurement accuracy Approximately 0.5%
Calibration guidance Calibrate if error exceeds 1%
Power supply options DC 4–5.5 V or DC 6–25 V
Operating current Approximately 10–13 mA
Communication interface RS485
Communication protocol Modbus RTU
Read function codes 03 / 04
Write function codes 06 / 16
Connection type Screw-terminal block
Dimensions Approximately 41.5 × 20 × 6 mm
Weight Approximately 6.5 g

Specifications depend on the selected hardware variant. Confirm the exact input type, measurement scaling, power supply, and register map in the applicable R4IVB02 manual. The manufacturer's published listing should be consulted for the precise measurement increment of the current-input version.

4. How the R4IVB02 Works

The R4IVB02 measures an external analog signal, converts it into digital data through its ADC, and makes the measurement available to a Modbus RTU master over RS485.

A typical monitoring system consists of:

  1. An industrial sensor or transmitter.

  2. The Eletechsup R4IVB02 analog input module.

  3. An RS485-to-USB adapter, PLC, or Modbus gateway.

  4. Host software for measurement display, data logging, or automation.

For example, two 4–20 mA transmitters can be connected to the two current-input channels. A computer or PLC can then periodically read the corresponding Modbus registers to obtain the measured values.

The software can convert these readings into meaningful engineering units, such as pressure in bar, temperature in degrees Celsius, or liquid level in metres, according to the connected sensor's calibration range.

The R4IVB02 is an input acquisition module, not a current output generator. It reads external signals rather than generating 4–20 mA control outputs.

5. GitHub Integration: Home Assistant and Modbus RTU

GitHub provides a practical software reference for integrating the R4IVB02 into monitoring applications.

Repository: arturmietek/ha-modbus-manager

This open-source project provides a Modbus RTU integration for Home Assistant, including a shared device library and YAML device definitions. Its documented device library includes eletechsup_r4ivb02.yaml, identified as an Eletechsup R4IVB02 two-channel current input device for 4–20 mA signals.

This is useful for developers who want to display industrial sensor readings on a home automation dashboard without writing an entire Modbus integration from scratch.

Potential Home Assistant Applications

The R4IVB02 can be used with compatible hardware and software configurations to support:

  • Monitoring 4–20 mA industrial transmitters.

  • Displaying sensor readings on a Home Assistant dashboard.

  • Recording historical measurement data.

  • Triggering automations when readings exceed configured thresholds.

  • Combining industrial measurements with other Modbus devices in one monitoring system.

For example, a compatible pressure transmitter can be connected to one input channel. The software can read the measurement and present it as a Home Assistant sensor entity, with the pressure value calculated from the transmitter's specified range.

The second channel can monitor another compatible current-output sensor.

Typical Integration Workflow

  1. Connect the R4IVB02 to a suitable RS485 adapter or gateway.

  2. Supply the correct voltage for the selected hardware version.

  3. Configure the module's Modbus slave address and serial communication settings.

  4. Install or configure the Home Assistant Modbus integration.

  5. Use the repository's R4IVB02 device definition as a reference.

  6. Verify the register addresses, measurement scaling, and returned values against the manufacturer's manual.

  7. Compare the software readings with a calibrated reference instrument.

GitHub device library: https://github.com/arturmietek/ha-modbus-manager

6. Python Integration for Custom Monitoring Applications

For developers building their own monitoring software, the R4IVB02 can be integrated with Python through a compatible Modbus RTU library.

The GitHub project ul-gh/cheap_modbus_rtu provides another software reference for working with Eletechsup Modbus devices.

A generic PyModbus example is shown below:

from pymodbus.client import ModbusSerialClient

client = ModbusSerialClient(
    port="/dev/ttyUSB0",
    baudrate=9600,
    parity="N",
    stopbits=1,
    bytesize=8,
    timeout=1
)

if client.connect():
    # Illustrative example only.
    # Verify the actual register address,
    # function code and scaling in the manual.
    response = client.read_input_registers(
        address=0,
        count=2,
        device_id=1
    )

    if not response.isError():
        print("Raw measurements:", response.registers)
    else:
        print("Modbus read failed")

    client.close()

This example demonstrates the general communication workflow, not a verified, ready-to-run R4IVB02 register-reading script. The register address, quantity, slave ID, baud rate, and function code must be checked against the module's documentation. Depending on the register map, the measurements may require function code 03 or 04.

After retrieving the raw values, the application must apply the correct scaling and conversion rules before treating them as engineering measurements.

With suitable software, the readings can be saved to a database, displayed on a dashboard, or forwarded to a supervisory control system.

7. Practical Applications

Industrial Pressure Monitoring

Many industrial pressure transmitters use a 4–20 mA output because current-loop signalling is suitable for long cable runs and industrial environments.

The R4IVB02 current-input version can acquire compatible transmitter signals and transfer the readings to a PLC, computer, or monitoring gateway.

For a linear pressure transmitter with a 0–10 bar range, the current-to-pressure relationship can be calculated as:

[
P=\frac{I-4}{16}\times 10
]

where (P) is pressure in bar and (I) is the measured current in milliamps. This formula assumes the transmitter maps 4 mA to 0 bar and 20 mA to 10 bar.

Liquid-Level and Flow Monitoring

Compatible current-output level and flow transmitters can be connected to the module for remote measurement. Software can convert the acquired current into a liquid-level or flow-rate value according to the transmitter's rated range.

Temperature and Process Monitoring

Where a temperature transmitter provides a compatible 4–20 mA or 0–20 mA output, the R4IVB02 current-input version can acquire its signal.

The module should not be assumed to accept a bare thermocouple or PT100 sensor directly. Such sensors generally require suitable signal conditioning or a transmitter compatible with the selected input version.

Smart Home and Building Automation

Through RS485 and compatible Home Assistant software, the module can connect industrial current-output sensors to a broader building monitoring system.

Possible projects include water-system monitoring, tank-level measurement, equipment status monitoring, and custom environmental sensing.

OEM Equipment and Embedded Systems

Its small PCB size and screw-terminal connections make the R4IVB02 useful for custom electronic equipment, compact control boxes, and embedded data acquisition systems that require two analog input channels.

8. Why Choose Eletechsup R4IVB02?

The R4IVB02 combines two analog input channels, a 12-bit ADC, RS485 communication, and Modbus RTU support in a compact, cost-conscious design.

Its main advantages include:

  • Two-channel acquisition for compatible industrial signals.

  • Current-input versions for 0–20 mA and 4–20 mA transmitters.

  • Separate voltage-input configurations for 0–5 V and 0–10 V signals.

  • Multiple supply-voltage options.

  • Screw-terminal connections for practical installation.

  • Public GitHub references for Home Assistant and Python-based integration.

  • Suitability for embedded monitoring and OEM applications.

Before purchasing, engineers should confirm the exact variant, supply voltage, sensor wiring, input range, register mapping, accuracy, and any electrical isolation requirements.

Conclusion

The Eletechsup R4IVB02 is a compact two-channel analog acquisition module designed for current and voltage measurement in industrial monitoring, embedded control, and remote data acquisition applications.

Its 4–20 mA current-input version is particularly useful for compatible industrial transmitters, while RS485 and Modbus RTU make the module accessible to PLCs, computers, and software-based monitoring systems.

The public GitHub project ha-modbus-manager provides a practical reference for integrating the current-input version into Home Assistant. Python Modbus libraries offer another path for developers creating customized measurement and data-logging applications.

For engineers seeking an economical two-channel analog input interface, the R4IVB02 offers a compact solution for bridging industrial sensors and software-based monitoring systems.

Official product information: Eletechsup R4IVB02

GitHub — Home Assistant Modbus integration: https://github.com/arturmietek/ha-modbus-manager

GitHub — Python Modbus RTU library: https://github.com/ul-gh/cheap_modbus_rtu

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