Heated-tank process control PCBA

Applications

Board architecture

The 215 × 130 mm, four-layer board uses an STM32G474RET6 controller, two MAX31865 Pt100 interfaces, an ADS1115 analog front end and MCP4728-based analog outputs. TPS26600 input protection and TMUX7412F analog protection are included. Field I/O uses 24 V; mains power stays in the external cabinet.

Electrical interfaces

Control sequence

A start request moves through filling and circulation proof before heating. The PI loop defaults to Kp = 5 and Ki = 0.02, with a 2 s zero-cross SSR window. Tune the loop to the installed tank, mixing and thermal losses. Fault reset clears the fault latch; it does not start the heater.

1. Stopped
2. Fill to 70%
3. Prove circulation
4. Enable contactors
5. Heat & hold
6. Stop / latched fault

Process settings & permissives

Flow ≥3 L/min and a continuous 1 s flow-switch proof precede heating. Pressure ≥0.30 bar, software temperature ≥90 °C, lost permissives, stale sensor data, contactor feedback faults or a 30 min fill timeout stop the process. The independent STB trips at 95 °C and uses manual reset below 90 °C.

Accessory selection

The system selection contains 71 per-unit purchasing lines and 11 factory-tool lines. Models, quantities, installation constraints and manufacturer URLs are recorded for each item. The table below exposes every line; the workbook provides the full purchasing layout. Configured probes and custom metalwork use the listed ordering specifications and matching interface drawings.

Detailed selection notes below are the Chinese engineering source. Model codes, quantities and manufacturer links are shared across languages.

Installation & wiring

Supply the board at J1 with 24 V DC and 0 V. Connect Pt100 probes to J4/J5 using equal-length three-wire leads. Supply instruments from the protected sensor branch; for AI1–AI3 leave connector pin 1 insulated, connect signal to pin 2 and return to pin 3. Low-side outputs drive the selected SSR input and intermediate relays, not mains loads.

230 V L/N → isolator Q0 → Type A RCBO QF0 → heater breaker QF1 → K1 → K2 → heater, with SSR1 in the L conductor after K2. Both contactors interrupt L and N. PE runs continuously to the cabinet, tank, pump and heater. Keep AC, 24 V, RTD and analog wiring in separate terminal groups and routes; do not bridge N to 0 V.

STB health, low-level health and pressure health feed SR1 through the independent hardware permit chain. Emergency-stop channels and contactor mirror contacts feed the restart monitor. Filling uses a normally closed valve with emergency-stop and high-level power interruption. Restoring a permit requires a deliberate reset and a separate start command.

Tank reference: 316L, inner Ø400 × 800 mm, 2 mm shell / 3 mm bottom, 25 mm insulation and 250 mm legs. H0 is the internal bottom. Heater H100; independent STB probes H160; low level H250; process Pt100 H300; working level H560; high level H680; overflow H720. Independent DN25 vent and overflow remain open, with an unsealed lid.

Use a short DN15 circulation loop, total length ≤2 m and ≤4 bends. Allow 5D upstream / 2D downstream of the flow meter. Keep the fill filter and check valve out of the low-head circulation loop. The selected pump must produce the required ≥3 L/min with the installed piping. SM6120 requires water conductivity ≥20 µS/cm; use a different measurement method for deionized water.

HMI & communication

Weintek MT8072iP V2: 800 × 480 display, 192 × 138 mm panel cutout, 24 V supply. COM2 two-wire RS485 uses 19200 baud, 8E1, slave 1 and zero-based Modbus addressing. DB9 pin 2 D+ → J15.1 A; pin 1 D− → J15.2 B; pin 5 reference → J15.3 GND_ISO. Fit 120 Ω termination only at the two bus ends; bond the cable shield at the cabinet side.

Read holding registers 0–11 with FC03. Write the temperature setpoint at PDU 256 and a single command at 257 with FC06; command 1=start, 2=stop, 3=reset. Do not use FC16. Refresh every 500 ms; after three consecutive communication timeouts show stale data and inhibit start/setpoint writes. The operator screen does not replace the independent hardware permit chain.

Sizing & calibration

Technical downloads

Download the complete KiCad, firmware, HMI, mechanical, wiring and factory documentation bundle, or choose individual files. The engineering handbook and purchasing workbook are in Chinese; interface tables use common signal names and model codes. File sizes and SHA-256 checksums are supplied for verification.

Application questions

Manufacturer references