ModBus reader

This tool is dedicated to the reading of metrics from one or several controller via Modbus TCP.

It helps to:

• optimize the reading of contiguous registers in one call (max. 123 registers)
• use the same TCP connection if the reading occur on the same second
• keep the number of TCP connections to maximum one per controller

Example of use:

// Create your ModbusReader with initial configuration
const reader = new ModbusReader([{
    name: "main_ctrl",
    address: "127.0.0.1",
    port: 502,
    slaveId: 1,
    valueItemInfos: [
        { id: "M_001", label: "Vln_avg", address: 171, type: "UINT32", unit: "V", coefficient: 1, recurrence: "* * * * * *" },
        { id: "M_002", label: "kW_tot", address: 203, type: "INT32", unit: "kW", coefficient: 1, recurrence: "* * * * * *" },
    ]
}]);
 
// Set your listener for every single value
reader.addValueListener((v) => {
    console.log(`R${v.valueItem.address} = ${v.data} (${v.valueItem.controller.name} - ${v.time.toISOString()})`);
});
 
// Start reading
reader.start();
 
// Stop reading
reader.stop();

You would be able to switch the configuration on the fly:

console.log("Ask for change");
await reader.restartWithNewConfiguration(/* new configuration */);
console.log("Changed");

Create a configuration

The ModbusReader accept a list of controller with the following attributes:

{
    name: "main_ctrl", // Name of your controller
    address: "127.0.0.1", // Address of your controller
    port: 502, // From which port you would read (refers to your Modbus device)
    slaveId: 1, // Refers to your Modbus device
    valueItemInfos: [] // List of metrics you want to read
}

Then you will need to fill the valueItemInfos attribute with a list of ValueItem objects:

{
    id: "M_001", // Reference for your use
    label: "Vln_avg", // Name of the register
    address: 171, // Where the register is placed on the device
    type: "UINT32", // What should be read (INT16, UINT16, INT32, UINT32 or FLOAT32)
    unit: "V", // Unit of what is read
    coefficient: 1, // Coefficient adjustement applied to the value
    recurrence: "* * * * * *" // Cron-based recurrence syntax with seconds
}

Current limitations

There is currently some limitations:

• If two reading operation with different recurrence occur at the same time, no optimizations in reading operation will occur.
• Reapply an heavy configuration can postpone some operations.
• Debouncing used to restrict Modbus TCP connection usage will add at least 20ms (can't be configured currently) to the scheduled time.
• The theoretical limitations of 123 registers per call can't be tweaked currently.

Contributions

This repository is open to pull requests. This project is using TypeScript, tests would be added in short future.

npm install
npm run build