Industrial Modbus SCADA

Build a lightweight SCADA system to monitor and control PLCs, VFDs, and other Modbus devices. Read holding registers for process values, write coils for remote control, log all data to PostgreSQL, and visualize on a real-time dashboard with gauges and charts.

Flow Architecture

=== READ PATH (Monitoring) ===

[Inject: 1s poll] --> [Modbus Read] --> [Function: Scale Values] --> [PostgreSQL: INSERT] --> [Chart]
                     (HR 40001-40010)    (raw to eng. units)          (readings table)          |
                                                |                                          [Gauge]
                                                v
                                         [Debug: Values]

=== WRITE PATH (Control) ===

[Dashboard Button] --> [Function: Build Command] --> [Modbus Write]
  "Start Pump"          (coil address + value)        (write coil)

What You'll Need

Modbus Register Map

The register map defines how raw Modbus values map to real-world process values. This example uses a typical PLC/process controller layout. Adjust addresses and scale factors based on your actual device documentation.

Step-by-Step Setup

# Test Modbus TCP connectivity
ping 192.168.1.100

# For RTU, find the serial port
ls /dev/ttyUSB*
# Typically: /dev/ttyUSB0

# Test with modbus-cli (optional)
# pip install modbus-cli
modbus --host 192.168.1.100 --port 502 read 40001 10

-- Create database
CREATE DATABASE scada_monitor;

-- Connect and create table
\c scada_monitor;

CREATE TABLE readings (
    id SERIAL PRIMARY KEY,
    timestamp TIMESTAMPTZ DEFAULT NOW(),
    temperature DECIMAL(5,1),
    pressure DECIMAL(5,2),
    flow_rate DECIMAL(6,1),
    tank_level DECIMAL(4,1),
    motor_speed INTEGER,
    motor_current DECIMAL(5,2),
    voltage DECIMAL(5,1),
    power INTEGER,
    run_hours INTEGER,
    status_word INTEGER
);

-- Create index for time-based queries
CREATE INDEX idx_readings_timestamp
  ON readings (timestamp DESC);

-- Optional: auto-delete old data (keep 90 days)
CREATE EXTENSION IF NOT EXISTS pg_cron;
SELECT cron.schedule('cleanup-old-readings',
  '0 3 * * *',
  $$DELETE FROM readings WHERE timestamp < NOW() - INTERVAL '90 days'$$
);

Function Node: Scale Raw Values

This function converts raw Modbus register values to engineering units using the register map configuration:

// Scale raw Modbus register values to engineering units
// Input: msg.payload = array of 10 raw UINT16 values from registers 40001-40010

var raw = msg.payload;

// Register map: [index, name, scale_divisor, unit, signed]
var registerMap = [
    [0, "temperature",   10,   "C",     true ],
    [1, "pressure",      100,  "bar",   false],
    [2, "flow_rate",     10,   "L/min", false],
    [3, "tank_level",    10,   "%",     false],
    [4, "motor_speed",   1,    "RPM",   false],
    [5, "motor_current", 100,  "A",     false],
    [6, "voltage",       10,   "V",     false],
    [7, "power",         0.1,  "W",     false],
    [8, "run_hours",     1,    "hours", false],
    [9, "status_word",   1,    "",      false]
];

var scaled = {};

registerMap.forEach(function(reg) {
    var idx = reg[0];
    var name = reg[1];
    var scale = reg[2];
    var unit = reg[3];
    var signed = reg[4];

    var value = raw[idx];

    // Handle signed INT16
    if (signed && value > 32767) {
        value = value - 65536;
    }

    // Apply scaling
    if (scale >= 1) {
        scaled[name] = Math.round((value / scale) * 100) / 100;
    } else {
        scaled[name] = Math.round(value / scale);
    }

    scaled[name + "_unit"] = unit;
});

// Decode status word bits
var statusWord = raw[9];
scaled.status = {
    running:  !!(statusWord & 0x01),
    fault:    !!(statusWord & 0x02),
    ready:    !!(statusWord & 0x04),
    auto:     !!(statusWord & 0x08),
    remote:   !!(statusWord & 0x10)
};

scaled.timestamp = new Date().toISOString();
msg.payload = scaled;

return msg;

Configuration Details

Complete Flow JSON

Copy and import this flow into EdgeFlow via Menu → Import.

{
  "name": "Industrial Modbus SCADA",
  "nodes": [
    {
      "id": "inject_poll",
      "type": "inject",
      "name": "Poll 1s",
      "interval": 1,
      "intervalUnit": "s",
      "repeat": true,
      "x": 120,
      "y": 180
    },
    {
      "id": "modbus_read",
      "type": "modbus-read",
      "name": "Read Holding Registers",
      "server": "modbus_tcp_server",
      "functionCode": "3",
      "startAddress": 0,
      "quantity": 10,
      "x": 340,
      "y": 180
    },
    {
      "id": "modbus_tcp_server",
      "type": "modbus-tcp-config",
      "name": "PLC",
      "host": "192.168.1.100",
      "port": 502,
      "unitId": 1,
      "reconnectTimeout": 5000
    },
    {
      "id": "func_scale",
      "type": "function",
      "name": "Scale to Eng. Units",
      "code": "var raw = msg.payload;\nvar registerMap = [[0,'temperature',10,'C',true],[1,'pressure',100,'bar',false],[2,'flow_rate',10,'L/min',false],[3,'tank_level',10,'%',false],[4,'motor_speed',1,'RPM',false],[5,'motor_current',100,'A',false],[6,'voltage',10,'V',false],[7,'power',0.1,'W',false],[8,'run_hours',1,'hours',false],[9,'status_word',1,'',false]];\nvar scaled = {};\nregisterMap.forEach(function(reg) { var value = raw[reg[0]]; if (reg[4] && value > 32767) value -= 65536; scaled[reg[1]] = reg[2] >= 1 ? Math.round((value / reg[2]) * 100) / 100 : Math.round(value / reg[2]); });\nvar sw = raw[9]; scaled.status = { running: !!(sw & 1), fault: !!(sw & 2), ready: !!(sw & 4) };\nscaled.timestamp = new Date().toISOString();\nmsg.payload = scaled;\nreturn msg;",
      "x": 580,
      "y": 180
    },
    {
      "id": "pg_insert",
      "type": "postgresql",
      "name": "Log to PostgreSQL",
      "host": "localhost",
      "port": 5432,
      "database": "scada_monitor",
      "user": "edgeflow",
      "password": "YOUR_PASSWORD",
      "query": "INSERT INTO readings (temperature, pressure, flow_rate, tank_level, motor_speed, motor_current, voltage, power, run_hours, status_word) VALUES ($1,$2,$3,$4,$5,$6,$7,$8,$9,$10)",
      "queryParams": "payload.temperature,payload.pressure,payload.flow_rate,payload.tank_level,payload.motor_speed,payload.motor_current,payload.voltage,payload.power,payload.run_hours,payload.status_word",
      "x": 820,
      "y": 140
    },
    {
      "id": "gauge_temp",
      "type": "gauge",
      "name": "Temperature",
      "group": "SCADA Dashboard",
      "label": "Temperature",
      "unit": "°C",
      "min": -40,
      "max": 150,
      "property": "payload.temperature",
      "x": 820,
      "y": 220
    },
    {
      "id": "gauge_pressure",
      "type": "gauge",
      "name": "Pressure",
      "group": "SCADA Dashboard",
      "label": "Pressure",
      "unit": "bar",
      "min": 0,
      "max": 25,
      "property": "payload.pressure",
      "x": 820,
      "y": 290
    },
    {
      "id": "chart_trend",
      "type": "chart",
      "name": "Trend Chart",
      "group": "SCADA Dashboard",
      "chartType": "line",
      "label": "Process Trends",
      "x": 820,
      "y": 360
    },
    {
      "id": "debug_values",
      "type": "debug",
      "name": "Scaled Values",
      "x": 820,
      "y": 430
    },
    {
      "id": "btn_start",
      "type": "button",
      "name": "Start Pump",
      "group": "SCADA Dashboard",
      "label": "Start Pump",
      "color": "#10b981",
      "x": 120,
      "y": 500
    },
    {
      "id": "btn_stop",
      "type": "button",
      "name": "Stop Pump",
      "group": "SCADA Dashboard",
      "label": "Stop Pump",
      "color": "#ef4444",
      "x": 120,
      "y": 570
    },
    {
      "id": "func_write_start",
      "type": "function",
      "name": "Coil ON",
      "code": "msg.payload = { address: 0, value: true };\nreturn msg;",
      "x": 340,
      "y": 500
    },
    {
      "id": "func_write_stop",
      "type": "function",
      "name": "Coil OFF",
      "code": "msg.payload = { address: 0, value: false };\nreturn msg;",
      "x": 340,
      "y": 570
    },
    {
      "id": "modbus_write",
      "type": "modbus-write",
      "name": "Write Coil",
      "server": "modbus_tcp_server",
      "functionCode": "5",
      "x": 580,
      "y": 535
    }
  ],
  "connections": [
    { "from": "inject_poll", "to": "modbus_read" },
    { "from": "modbus_read", "to": "func_scale" },
    { "from": "func_scale", "to": "pg_insert" },
    { "from": "func_scale", "to": "gauge_temp" },
    { "from": "func_scale", "to": "gauge_pressure" },
    { "from": "func_scale", "to": "chart_trend" },
    { "from": "func_scale", "to": "debug_values" },
    { "from": "btn_start", "to": "func_write_start" },
    { "from": "btn_stop", "to": "func_write_stop" },
    { "from": "func_write_start", "to": "modbus_write" },
    { "from": "func_write_stop", "to": "modbus_write" }
  ]
}

Expected Output

The function node outputs scaled engineering values every second:

{
  "payload": {
    "temperature": 42.5,
    "temperature_unit": "C",
    "pressure": 3.82,
    "pressure_unit": "bar",
    "flow_rate": 125.3,
    "flow_rate_unit": "L/min",
    "tank_level": 67.8,
    "tank_level_unit": "%",
    "motor_speed": 1480,
    "motor_speed_unit": "RPM",
    "motor_current": 12.45,
    "motor_current_unit": "A",
    "voltage": 398.2,
    "voltage_unit": "V",
    "power": 8650,
    "power_unit": "W",
    "run_hours": 12847,
    "run_hours_unit": "hours",
    "status": {
      "running": true,
      "fault": false,
      "ready": true
    },
    "timestamp": "2026-02-12T14:30:00.000Z"
  }
}

Troubleshooting