Need to monitor four temperature points and read the actual resistance values of PT100 or PT1000 sensors using one industrial communication interface?

Eletechsup PTDNC04 is a 4-channel RTD acquisition module designed to collect both temperature and resistance measurements from PT100/PT1000 sensors and transmit the data through RS485 Modbus RTU.

Unlike a temperature-only monitoring device, the PTDNC04 provides access to both calculated temperature values and measured sensor resistance values, making it useful for applications that require additional measurement diagnostics, sensor evaluation or custom data processing.

1. Key Features of the PTDNC04

• 4 independent acquisition channels: Collect measurements from up to four compatible PT100/PT1000 sensors.

• PT100 and PT1000 support: Compatible with 2-wire and 3-wire sensor configurations.

• Temperature and resistance measurement: Read temperature values and corresponding RTD resistance values through Modbus registers.

• RS485 Modbus RTU: Integrate with compatible PLCs, industrial PCs, HMI systems and embedded controllers.

• Wide temperature range: Version A supports -40°C to +220°C; Version B supports -40°C to +500°C. Choose the version that matches the required measurement range.

• Configurable serial communication: Baud rates from 1200 to 115200 bps, with 9600 bps as the default.

• Multi-module networking: Configure device addresses for multi-module systems; the manufacturer specifies support for up to 247 addresses, with an RS485 repeater recommended when connecting more than 16 modules.

• Temperature and resistance correction: Dedicated registers allow correction values to be written when calibration adjustments are required.

2. Real Modbus Register Map

The PTDNC04 documentation provides separate register groups for temperature and resistance acquisition.

Register address	Function	Data unit
0x0000–0x0003	CH0–CH3 temperature values	0.1°C
0x0020–0x0023	CH0–CH3 PT100/PT1000 resistance values	0.1Ω
0x0040–0x0043	Temperature correction values	0.1°C
0x0060–0x0063	Resistance correction values	0.1Ω

For example, a temperature register value of 255 represents 25.5°C. A resistance register value of 1000 represents 100.0Ω.

The module supports Modbus function code 03 for reading registers and function codes 06 and 16 for writing supported parameters. Confirm the documented register behavior and signed-data handling before implementing your software.

3. Why Read Resistance as Well as Temperature?

Reading resistance values can provide useful information beyond the displayed temperature.

RTD Sensor Diagnostics

Engineers can compare measured resistance with expected PT100/PT1000 characteristics to help investigate wiring problems, sensor mismatches or unexpected readings.

Custom Temperature Conversion

Applications that need additional processing can retrieve the resistance measurement and apply their own conversion or validation logic, provided the measurement characteristics and calibration requirements are understood.

Calibration and Measurement Verification

Separate temperature and resistance correction registers provide a way to adjust readings when appropriate. Calibration should be performed using a suitable reference instrument and a documented procedure.

Multi-Point Temperature Monitoring

Four channels allow measurements at different locations to be collected by one Modbus slave, reducing the need for four separate communication interfaces at the controller.

4. Practical Industrial Applications

Industrial equipment monitoring: Measure temperatures at several points in a machine, enclosure or test fixture.

Heating and thermal process monitoring: Acquire RTD measurements for compatible heating equipment and temperature-control systems.

Laboratory and test equipment: Record multiple temperature points and examine resistance values during experiments or sensor evaluation.

HVAC and environmental monitoring: Collect temperature readings from several locations for use in a compatible monitoring or building-management system.

Warehouse and equipment-room monitoring: Bring several RTD measurements into a PLC, industrial computer or data logger through RS485.

Custom automation systems: Combine PTDNC04 readings with software alarms, trend logging, HMI displays or higher-level control logic.

The suitability of each application depends on the selected sensor, installation environment, required accuracy and electrical design.

5. Integrating PTDNC04 with a PLC or Industrial PC

A typical system consists of:

PT100/PT1000 sensors → PTDNC04 → RS485 bus → Modbus RTU master → HMI, SCADA or data-logging application.

To integrate the module:

1. Select the appropriate temperature-range version.

2. Wire each sensor according to the documented 2-wire or 3-wire configuration.

3. Connect the module's RS485 interface to a compatible Modbus master.

4. Configure the serial parameters and device address.

5. Read temperature registers 0x0000–0x0003.

6. Read resistance registers 0x0020–0x0023 when resistance data is needed.

7. Apply the documented scaling and implement communication-error handling.

The PTDNC04 uses a default serial configuration of 9600 baud, no parity, 8 data bits and 1 stop bit.

6. Important Engineering Considerations

The specified module measurement accuracy is 1%. This should not be confused with the nominal accuracy of an individual PT100/PT1000 sensing element. The complete measurement system also depends on sensor tolerance, wiring, installation, calibration and operating conditions.

For the best results:

• Select the narrower measurement range that comfortably covers your application.

• Follow the manufacturer's wiring instructions for 2-wire or 3-wire sensors.

• Keep RS485 wiring and grounding appropriate for the installation.

• Verify the resistance and temperature register scaling.

• Recalibrate if the measured deviation requires correction.

• Ensure that the selected sensor probe and cable are rated for the actual environment.

7. Choose the Eletechsup PTDNC04 for Multi-Channel RTD Acquisition

If your project needs four-channel PT100/PT1000 measurement, RS485 communication and access to both temperature and resistance values, the PTDNC04 offers a compact acquisition solution for industrial monitoring, laboratory testing and custom automation.

Official product page:
https://eletechsup.com/products/ptdnc04-pt1000-4ch-modbus-wide-range-temperature-sensor

Technical protocol:
https://ww.naturnahleben.ch/manuals/PTDNC04%20PT1000%204CH%20Modbus%20Wide%20Range%20Temperature%20Sensor%20Collector%20RS485/PTDNC04%20Manual/PTDNC04%20Modbus%20Rtu%20Command.pdf

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