Simple ladder logic question

RickGilbert

Member
Join Date
May 2005
Posts
7
Hi all,
I'm new to the forum and novice at ladder logic programming so bare with me. Quite simply, I need help converting a normally closed contact input (from a PIR motion detector) to a normally open input.

I'm using WinTrilogi version 3.5.

Can anyone help?
 
Quite simply use a NO contact from your sensor if you have it or, in your program, use a ----] [----- or --------]/[-------- to suit the needs of your program. The two instructions above will let you have a true condition if the input is on, or if it is off.
 
The sensor contacts for the motion detector are normally closed.
Basically I need to convert the normally closed contacts from the Motion detector to a normally open contact in the program.
How do I accomodate this into the software?
 
Last edited:
If they are normally closed then power is ALWAYS going thru it unless it is triggered. If you want to trigger an action when the sensor OPENS then use -|/|- in the ladder, this instruction will not be true UNTIL the NC sensor OPENS.When doing this dont concentrate on the sensor/switch/device, just look at whether you need to know if input is ON or OFF and create the ladder accordingly.
 
Example

Here is an example. The contact in the starter is Normally Closed. In normal state the input I:0.0/1 is turned on, and its NC contact shown is open. The coil for the alarm B3:0/13, which could be an output or an internal coil, is off. The contact for this coil, B3:0/13 is open. This is the state shown.

When the starter trips the contact at the starter opens, the input I:0.0/1 at the PLC turns off, and the contact in the rung for Starter OK closes. This turns on the coil for B3:0/13 and its NO contacts will close.
 
rsdoran said:
If they are normally closed then power is ALWAYS going thru it unless it is triggered. If you want to trigger an action when the sensor OPENS then use -|/|- in the ladder, this instruction will not be true UNTIL the NC sensor OPENS.When doing this dont concentrate on the sensor/switch/device, just look at whether you need to know if input is ON or OFF and create the ladder accordingly.

Thanks for the help rsdoran. Yes, I do want to activate a relay when the NC contacts of the sensor OPEN. My confusion is coming from imagining current flowing from the motion detector through a NC contact and ALWAYS activating the relay which isn't what I desire. I need the relay to activate when the contacts of the motion detector open. Will using -|/|- in the ladder accomplish this? I hope my question isn't confusing. The concept of a NC sensor opening to activate a relay is a bit confusing.

Thanks for the help.
 
I dont like the relay thing but it works. Think about this, if you used your NC sensor to turn on a relay but wanted to trigger something...lets say turn on a light...when the sensor "opened". You would wire the light thru a NC contact on the relay...ie
Code:
---|/|-------------------------( )----
That same method applies to programming.

I see a new gif
Comingsoon.gif
.

See if this helps too: http://www.patchn.com/xio_xic_explained.htm
 
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This deal with a physical NO or NC switch and a virtual NO or NC contact in PLC (ie XIO or XIC in AB) confused me thoroughly at first.

Here is what I did to figure it out and keep it straight in my head.

Took a NC stop pushbutton wired it to input 0 (NC contact) and input 1 (NO) contact. Did same for NO start switch NC on input 3 and NO on input 4.
Input 0 was connected to output 0, 1 to 1 etc.

Then did scenarios
1. All power off how many and WHICH led on inputs and outputs lit
2. PLC power only same question
3. Now supply power to inputs same question
4. supply power to outputs -- same question

NOW push the stop button which ones turn on and off
Now push the start button same question.

That is how I figured it out.

Dan Bentler
 
Dan,
In this quote, you are still a little confused:
This deal with a physical NO or NC switch and a virtual NO or NC contact in PLC (ie XIO or XIC in AB) confused me thoroughly at first.

Normally Open contact symbol is not equal to the XIO function.
Normally Closed contact symbol is not equal to the XIC function.

NO = XIC (memory trick: "What you C is what you get")
NC = XIO (memory trick: "What you C is Opposite of what you get")
 
Agree with Lance

very simple think of it as it is stated...

XIC = Examine if closed.
XIO = Examine if open.

Nothing more... don't over complicate it...
 
Curses Fouled Up Again

Lancie1 said:
Dan,
In this quote, you are still a little confused:


Normally Open contact symbol is not equal to the XIO function.
Normally Closed contact symbol is not equal to the XIC function.

NO = XIC (memory trick: "What you C is what you get")
NC = XIO (memory trick: "What you C is Opposite of what you get")

Lancie

It was late at nite and I TRIED to ensure I was not indentifying XIC with XIO or saying XIC is,,,,,,, XIO is ,,,,,,,,.
Sigh It is going to be so nice to be perfetc.

Tanx for memory trick.

Dan
 

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