Please stop what you are attempting.
What you have explained is how wire a sensor into a plc input under normal conditions.
What you have is a grain elevator which changes things all together. You will need to understand the national electrical code (NEC 70) which defines hazardous work locations and wiring methods. See sections 500, and 502. you alaso need the NFPA 79, electrical standard for electrical machinery. other rules may also apply.
Your area will be most likely a Class 2, Division 1 location which means that the dust in the grain elevator is in the air in such a quantity that if you light a match or create a spark, the dust will ignite and create a fire.
To prevent this chance of ignition, you must use an intrensically safe barrier between the plc and the sensor.
You also must use rigid conduit wiring, intrensically safe sensors, conduit seals, an a host of other things to deal with.
Please study up on this and get with an engineer, safety authority, electrical authority, or local plc rep for his help with safety devices.
I do not know your electrical requirements there, but a grain elevator makes a big mess when it explodes. I saw the mess after one wxploded.
regards,
james.