DeviceNet to PROFINET Gateway for Solar Welding Pressure Control

Project Background: Upgrading a TOPCon Solar Stringer Line

A major photovoltaic module manufacturer in East China recently expanded its production capacity with a new 2 GW TOPCon solar cell stringer workshop. The facility houses 16 high-speed stringer machines that require precise control over the dynamic contact pressure between the soldering ribbon and the solar cell. The target pressure is 0.85 MPa with a tolerance of ±0.05 MPa. Any deviation beyond this range can increase the rate of cold solder joints and micro-cracks by 0.3%, directly impacting module efficiency and long-term reliability.

The existing stringers were originally equipped with DeviceNet-based pressure sensors (model 836P-D2NMGC18M) from Rockwell Automation/Allen-Bradley. These sensors communicate via the DeviceNet protocol and have been in service since 2008. The new Manufacturing Execution System (MES) and the plant’s central controller, a Siemens SIMATIC S7-1200 1215C DC/DC/DC PLC (6ES7 215-1HG40-0XB0), exclusively support PROFINET. Replacing all 16 sensors with PROFINET-compatible models would have been costly and time-consuming. Instead, the engineering team opted for an industrial protocol conversion gateway that acts as a DeviceNet master and a PROFINET slave, enabling seamless data exchange between the legacy sensors and the modern PLC.

System Components and Network Topology

The solution revolves around a compact yet powerful gateway that bridges the two industrial networks. Below are the key hardware and software elements:

Step-by-Step Implementation

1. Hardware Wiring and Power

The DeviceNet trunk cable (red = CAN_H, black = CAN_L, bare shield) was connected to the gateway’s 5-pin terminal block. Because the gateway already includes an internal 120 Ω termination resistor, no external resistor was needed. The 24 VDC power supply was sourced from the existing machine’s power module, ensuring a common ground with a measured ground resistance of 0.8 Ω. On the PROFINET side, a shielded CAT6 cable linked the gateway to a Siemens Scalance XC206 switch. The IP addresses were assigned as follows: gateway 192.168.10.112, PLC 192.168.10.10, subnet 255.255.255.0.

2. TIA Portal Configuration

The gateway’s GSDML file (version 2.3) was imported into TIA Portal V19. After adding the device to the PROFINET network, the device name was set to “DNTM_PN_01” and the update cycle was configured for 4 ms (RT mode, as the S7-1200 does not support IRT). The I/O mapping was defined as follows:

After compiling and downloading, the online status showed LinkStatus=Up and IOState=DataExchange with no errors.

3. Gateway Configuration via USB

Using the gateway’s configuration software (connected via USB-C debug port), the DeviceNet master mode was activated. A network scan detected only the sensor at MAC ID 12. The EDS file for the 836P sensor was imported, which automatically parsed the 6-byte I/O assembly: bytes 0–3 for the single-precision floating-point pressure value, byte 4 for status, and byte 5 for alarm bits. The polling cycle was set to 5 ms, and the fail-safe mode was configured to “hold last value.” The data was mapped to PROFINET input offsets 0–5. After downloading, the gateway’s RUN LED turned solid green and the DN LED flashed at 1 Hz, indicating normal data exchange.

4. Closed-Loop Pressure Control in PLC

A function block (FB1 “Pressure_Control”) was created and called every 8 ms. The logic performs the following steps:

• Reads the REAL value from the gateway input area and scales it to the physical range (0–1.6 MPa).
• Compares the measured pressure with the setpoint (0.85 MPa). If the deviation exceeds 0.05 MPa, the analog output (±10 V) adjusts the servo valve to regulate the cylinder pressure of the soldering head.
• If the deviation persists for 5 consecutive samples, an HMI alarm is triggered, the batch number is recorded, and the event is uploaded to the MES via OPC UA.

5. Noise Immunity and Diagnostics

To ensure reliable communication in the electrically noisy environment of a stringer machine, several measures were taken:

• Armored DeviceNet cable was used, with the shield grounded at the gateway end only. The communication cable was routed at least 20 cm away from high-current 50 Hz heating power lines.
• The gateway’s error counters and retry statistics were monitored. During commissioning, one machine exhibited a 3% message retry rate due to poor 24 V common grounding. After correcting the ground, retries dropped to zero.
• TIA Portal’s device diagnostics and topology view were enabled. If a DeviceNet break occurs, the gateway sends a diagnostic record (0x8B) to the PLC, which immediately stops the machine and displays the affected station number on the HMI. This reduced the mean time to repair from 15 minutes to 3 minutes.

Performance Results and Lessons Learned

After two months of continuous operation, the system has proven to be stable and accurate. The pressure control loop maintains the target 0.85 MPa within the required tolerance, and the cold solder joint rate has remained below the threshold. The following insights were gained:

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