wiring inputs (sourcing)

[whippee2]

Hello all, Just another question from a rookie. I am wiring up a compact logix for a new grain elevator installation at work. My question is: how do i connect a sensor to a digital input card. the card will be sourcing so i have connected +24vdc to the common terminal of the card. Now with the two core cable to the sensor, do I connect one core to the input terminal (the correct channel that is), and the other core to -24vdc?

Thanks again
Whippee

 

[Mickey]

It would help if you provide us with the catalog number of your input card.
And a link to the manual of your sensor ( or snap shot of its wiring diagram)

 

[James Mcquade]

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.

 

[whippee2]

ye I am aware of the safety requirements when working in these conditions. Anyhow I spoke again to the engineer yesterday and I asked hime about these levels sensors and he corrected himself and said we will be using the input card in a sinking situation. Therefore I wired my -24vdc to the common terminal, +24vdc will go out to the sensor and the return wire will connect into the appropriate input terminal.
Thanks for the replies.
Ye when I was inducted to work in this grain mill, we watched a video and saw some grain elevators explode, quite the mess for extremely dangerous. I was speaking with the operators and they told me up until just a few years ago they were all smoking in the mill. Pretty lucky nothing happened, I would say.

Whippee