MettlerToledoOPCUA

OPC UA Server for Mettler Toledo Scales

Many of the various Mettler Toldeo Scales only have an RS232 interface which makes reading the data difficult if you are trying to connect the data from the scales into an MES system such as SAP ME (Manufacturing Execution) or SAP DMC (Digital Manufacturing Cloud). The good thing is that they all support the same basic commands detailed in this document - Mettler Toledo Standard Interface Commands.

This project is written in Javascript using the Node-OPCUA and SerialPort libraries.

NodeJS was selected due to its asynchronous nature and because it can be run on Window, Linux or Mac.

The project was developed and tested using Windows 10, NodeJS 14 and a Mettler Toledo Viper BC scale.

The plan is that this will also be tested on a Raspberry PI as this would provide a low cost method of adding OPC UA and ethernet capabilites to scales.

Install Procedure:

• Connect your scales to your PC/MAC/Raspberry PI using an RS232 port (If you have one) or a USB to serial adapter
• Install nodejs 14
• Clone all the files from here into your own directory
• Install the dependencies using

npm install node-opcua
npm install serialport
node mtServer portName baudRate

where portName is the port where the scales are connected (eg Com5 for Windows machines) and baudRate is the baudRate your scales are configured for (eg 9600 or 19200)

The OPC UA Server exposes the following tags

• DecodedResponse- String- Translation of the respose code from the scales into a more friendly message
• RawRespose- String- The raw data directly from the scales
• ReadStableWeight- Boolean- Writing 1 to this tag will trigger the scales to read the STABLE weight
• ReadWeightImmediate- Boolean- Writing 1 to this tag will trigger the scales to read the weight regardless if it is stable
• ReadWeightImmediateRepeat- Boolean- Stream the weight data constantly until you send another command to stop
• Reset- Boolean- Reset scales (replies with the serial number)
• SerialNumber- String- Serial number of the connected scales
• SerialPortConnected- Boolean- 1 when scales are connected (still work in progress)
• SoftwareVersion- String- Software version of the scales
• Tare- Boolean- Writing 1 to this tag will Tare the scales
• TareWeight- Float- The Tare weight
• TareWeightUOM- String The unit of measure for the tare weight
• Weight-Float- The weight from the scales
• WeightStable- Boolean- 1 = weight is stable, 0 = dynamic weight
• WeightUOM- String- Unit of measure for the weight
• Zero- Boolean- Writing 1 to this tag will zero the scales

This is the intial release where I have created my own OPC information model for the data but I plan to migrate that to to support the OPC UA Companion Specification for Weighing