0 to 24vdc to drive a discreet input to a plc.

Thread Starter

Jeff.M

Joined Dec 6, 2022
26
What is the source of the "0"? And what voltage does it have when it is not zero?? Are you able to edit the program on the PLC? Is there a 24 volt source available?
There are quite a few simple ways to achieve what is asked, but just asking that without any of the surrounding information is quite useless, really it is.
If that zero is an open switch to common, then the very simple thing will be to add a pull-up to 24 volts resistor.

That is all the advice you get until the questions are answered.
Thanks for the reply. I don't have the answer. All I was told is the circuit needs 24vdc when it senses paper instead
of 0 when it senses paper. The problem is they can't get the correct sensor so there trying to make this one work.
Thanks,

JM
 

MisterBill2

Joined Jan 23, 2018
18,167
REALLY!! We are not told anything about either the source of the voltage signal or the type of input. Is it sinking or sourcing or just voltage sensitive? Nor are we informed about the signal, is it a switch to ground? Or switched to +24 volts? or switched between the two? three quite different possible formats. And the ways to deal with them are different.
 

MisterBill2

Joined Jan 23, 2018
18,167
If the switching source can source 20 milliamps then possibly a resistive opto-relay can be assembled so the +24 lights up LEDs and pulls the input low with a resistive type photocell, and when the switch output is low the input would be pulled up to 24 by a pullup resistor.
 

vu2nan

Joined Sep 11, 2014
345
Would the PLC need a pullup, meaning could it be programmed into the PLC?
The PLC input by itself does not need a pull-up resistor. But the sensor, as described by the OP, does. Should the pull up resistor be internal to the sensor the external one wouldn't be required.

Nandu.
 

WBahn

Joined Mar 31, 2012
29,976
Thanks for the reply. I don't have the answer. All I was told is the circuit needs 24vdc when it senses paper instead
of 0 when it senses paper. The problem is they can't get the correct sensor so there trying to make this one work.
Thanks,

JM
Who wrote/maintains the code in the PLC?
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
Thats a great circuit but there is a problem. There is no voltage from the PLC. The circuit I need has to supply
the 24vdc.
Thanks again.
Is that simply because the input is sink input instead of source?
If so no extra circuit needed.
Again, PLC input module details would help!!
 

MisterBill2

Joined Jan 23, 2018
18,167
It seems that the TS is also burdened by a lack of information.
If the sensor information is available it may be possible to suggest a work-around connection that will solve the problem.
And that "four terminal" option i suggested is not complex or complicated, but it certainly demands an understanding of how it works.
 

Thread Starter

Jeff.M

Joined Dec 6, 2022
26
Thanks so much for your help.
The NPN version will work but it needs to sink at least .1A @24VDC. The circuit I built only sinks approximately 5ma. Is
there a circuit I can build that would meet these requirements?
Thanks in advance for your time and help.

Jeff.M
 

sghioto

Joined Dec 31, 2017
5,376
The NPN version will work but it needs to sink at least .1A @24VDC. The circuit I built only sinks approximately 5ma.
Can you post your circuit to verify?
I think it would be better to use the PNP version I posted in #25.
 
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Thread Starter

Jeff.M

Joined Dec 6, 2022
26
That is the circuit I used and when the input switched to 24
vdc the input to the PLC wouldn't go below 12.8vdc.
Thanks again,

Jeff M.
 
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