general dc input question

benji

Member

B

Join Date

Oct 2008

Location

syria , Aleppo

Posts

72

• Dec 28, 2008

• #1

do all PLCs take the tristated input as 0 logic?

 

bernie_carlton

Lifetime Supporting Member + Moderator

Join Date

Apr 2002

Location

Yakima, Washington

Posts

6,412

• Dec 28, 2008

• #2

I take your question to mean, 'Is a discrete input pin left open interpreted as the '0' state?'

'YES' for Allen Bradley SLC, Micrologix and ControlLogix. Also AutomationDirect 05, 06, 205, 405.

 

jvdcande

Member

Join Date

Apr 2002

Location

Menen

Posts

2,178

• Dec 28, 2008

• #3

That's also a yes for Siemens (S5, S7-200, S7-300/400), Omron CQM1, Mitsubishi FX and Philips PLC10 and PC20 (now Nyquist, I believe). In fact, I haven't seen any other situation so far and I've been active in this field of expertise for over 28 years now.

Kind regards,

 

BobB

Lifetime Supporting Member

Join Date

Jun 2002

Location

Sydney

Posts

4,550

• Dec 29, 2008

• #4

I cannot remember a PLC that I have used in the last 25 years that treated a discreet input pin left open differently quite frankly - have not used everything available of course but have used plenty.

 

benji

Member

OP

B

Join Date

Oct 2008

Location

syria , Aleppo

Posts

72

• Dec 29, 2008

• #5

thank you for your replies

 

parky

Member

P

Join Date

Oct 2004

Location

Midlands

Posts

5,730

• Dec 30, 2008

• #6

If you read the specs on the input cards it will tell you the threshold of the input voltage e.g. < 8.5v is logic 0 > 16.4v is logic 1 (these figures are not actual ones taken from input cards as these will vary from manufacturer).
PLC's are not like logic chips that can have a tri state