Hi, I am trying to read an analog input from the Siemens S7 1212C PLC. I can read and write the digital i/o just fine and I get the correct analog voltage to show in the Siemens TIA software with a norm_x and scale_x instruction. When I read the output from the scale_x function at address %MD100 with Node-RED s7 (ST-One) node, I get a number that seems unrelated to the real value. I suspect that it is encoded somehow. Does anyone here know how to convert this to a meaningful number?
For example, I feed the PLC with 3V at it's analog input. The Siemens TIA software shows at %MD100 a value of 2.987196, which is close enough. When I read this address with Node-RED, it shows me a number like this: 1077882425. The datatype on the PLC for this address is "Real".
Anyone any idea?
I have found the solution. Even when the address is %MD100 in the Siemens software, to read the floating point number in Node-RED you have to read MR100. That will show the correct analog input value.
