This is a board I made and put into service. It had a pot input and 4-20mA out. Many of these are in use and work well.
With a bit of work, the pot could be replaced with the ADXL 354 I think.

 

The use of A-to-D and D-to-A converters allow this system to convey both power and an analog signal (rather than just a binary signal) over a single twisted pair. Data is bidirectional.



Details:
http://cappels.org/dproj/Binary_Sig...naling_And_Power_Over_Pair_of_Conductors.html

 

Allow me to jump in here with some actual knowledge in the vibration monitoring field....

This is definitely an application for an industrial condition monitoring accelerometer. Many companies made these, with PCB Piezotrontics being the grand daddy of them all. Industrial accelerometers have integrated electronics, which PCB calls "ICP". The integrated electronics provide a low impedance AC signal from the accelerometer on a single shielded cable which also supplies constanant-current DC power to the accelerometer.

A very brief explanation of ICP operation:

A constant current power supply provides 2 – 5 mA with a compliance voltage of 24 volts. The ICP electronics in the accelerometer biases this current to approximately 12VDC. The AC signal from the accelerometer rides on this 12v bias with a maximum swing of about 7 volts at full scale – the AC signal modulates the 12v bias from around 5 volts to 17 volts. At the instrumentation end of the cable, a 10uF electrolytic capacitor blocks the DC signal and provides the AC signal for analysis.

Industrial accelerometers come in a range of sensitivities, frequency range, shapes and styles. For most machinery monitoring applications, a sensitivity of 100mV/g is suitable. An accelerometer with a sealed, integrated cable would probably be best for this application. Does the environment require an intrinsically safe installation? If so, there are many hoops to jump through.


A few examples:

https://www.ctconline.com/products/...elerometers/100-mv-g-standard-size/?prd=AC102

https://www.ctconline.com/products/...elerometers/100-mv-g-standard-size/?prd=AC104

https://www.pcb.com/industrial-sensors/accelerometers/low-cost-icp

 

The open question is what do you do with the signal at the other end. This can range from a single level to look at, in which case, an accelerometer with internal integration to provide an overall signal proportional to vibration velocity might be the best answer.

 

The solution was given in post #20, a loop powered transducer, eituher 4-20 mA or 10-50 mA, depending on how much power the sensor electronics require. That scheme has been around for MANY YEARS and it works very well. It is a fully mature technology, available from many suppliers.
The requirement is that the loop power supply have a high enough voltage to support the sensor electronics. The benefit is that it works even if the external wiring resistance changes, so the accuracy is maintained.