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Guru

Join Date: Oct 2007
Location: Sour Lake, TX 30°08'59.68"N 94°19'42.81"W
Posts: 671

06/26/2009 11:58 AM

This is an input module (1746-ITV16) for an Allen Bradley SLC-500 plc. As we can see, the external switches are connecting the respective input to ground (DC negative). I recognize the symbols on the left side, they are, simply, normally open contacts. Those on the right side are, also, normally open.

Can anybody tell me what is the symbol for right side contacts? Why it shows three connection (pins)? I didn't find what this symbol represents, all over the google coverage, so if anybody can illumine me, I would be in debt forever....

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Guru

Join Date: Oct 2007
Location: Sour Lake, TX 30°08'59.68"N 94°19'42.81"W
Posts: 671
#1

### Re: Allen Bradley I/O Module

06/26/2009 6:11 PM

Found it!

Sorry to bother, I'm in debt to nobody

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Guru

Join Date: May 2006
Location: Reading, Berkshire, UK. Going under cover.
Posts: 9687
#2

### Re: Allen Bradley I/O Module

06/26/2009 7:50 PM

Well done - have a GA for answering your own question so succinctly !

[Note that AB don't use the convention of "+ve at the top, -ve at the bottom", so you have to look out for the "+" or "-" in front of the ±DC.

Note also that the 16 inputs are all of the same type - you don't need to use 0,2,4.. for one type, and 1,3,5.. for the other (the types being solid state vs contact)].

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Guru

Join Date: Oct 2007
Location: Sour Lake, TX 30°08'59.68"N 94°19'42.81"W
Posts: 671
#3

### Re: Allen Bradley I/O Module

06/27/2009 8:30 AM

That's the pinnacle of irony refinement: to reward me being on the brink of stupidity

In Texas miles, you must be very close to the place where G.B. Shaw lived and created.

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Anonymous Poster
#4

### Re: Allen Bradley I/O Module

08/05/2009 1:46 AM

Dear Indel,

the module seems to be 24v dc sourcing , Please will you explain the concept of the contacts as in diagram how the circuit will work?

Regards

Guru

Join Date: May 2006
Location: Reading, Berkshire, UK. Going under cover.
Posts: 9687
#5

### Re: Allen Bradley I/O Module

08/05/2009 4:53 AM

Maybe this will help explain it:

Looking at the drawing on the left: when the switch is made, current flows from the external 24V sensor supply, through a current limiting resistor, through the LED part of the input optocoupler, then out of the PLC input terminal and through the switch contacts to 0V.

It's called a sourcing input because the input terminal supplies current to the sensor.

The drawing on the right shows the same set-up as on the left, but with the sensor supplied from within the PLC. In either case, it is called a sourcing input.

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