Does the 1400 have an ethernet port?

If so, perhaps this library? https://pypi.org/project/pycomm/

https://pypi.org/project/cpppo/

I've used PyLogix in the past, but it does not apply to Micrologix.

Having spent 3 years dealing with metal pressure sensors and hydrolysis caused damage between the load cell and metal body, I wouldn't go with this solution.

Is it possible to install an ultrasound sensor on top of the tank to measure the distance and calculate level?

Silly question, but why would you go with Modbus to talk to a Siemens PLC? Is it an old model without an ethernet port or is it used?

Unless someone has already decoded the protocol for you it may be easier to just buy a replacement. There's always the less obvious choice of recording the signals (there's only two after all) and repeat them without understanding the underlying protocol. http://scraplab.net/reverse-engineering-a-w...

The problem is that both your Pi's must know whether one is asking to use the bus or not. So you'd have to wire the chip select signal to both.

I see 6 components on that schematic.

Would a multiplexer not do the job and avoid interference between the modules?

http://e2e.ti.com/support/switches-mult ... -4-sensors
https://www.microchip.com/forums/m230553.aspx

The S7-1200 has an ethernet port... I would go through that solution. It should be possible for you to configure a UDP broadcast of the values you want and with a "simple" socket code in the Raspberry pi, catch those values. I have done similar using Java with UDP broadcasts from a Simatic...

Are you using Greg Copeland's library? Or the original Maniac Bug's? After looking into Maniac Bug's files (stupidly, as someone else found the same thing before) I found this: // Yay, we are done. // Power down powerDown(); //commented this line. // Flush buffers (Is this a relic of past experiment...