Hallo, i want ask something. how to read temperature from thermocouple 4-20mA? i use modbus rtu protocol to this. output value from sensor in node red like the picture in bellow. how to fix it? thanks before guys
Depends on which ADC (Analogue Digital Converter) card / method you are using to read the values. MCP3008, others. Are there direct Node-RED nodes.
I use WidgetLords cards and have been very pleased (no affiliation) with direct support for Raspberry Pi and Node-RED. They have multiple 4-20 ma cards for IO.
Some cards will need additional resistors or other changes specifically to read thermocouples / thermistors.