Japanese I\O

[wdd0422]

From what I have seen most Japanese equipment uses sinking I\O. This has never made sense to me, even dangerous. Even with a isolated supply if just one input becomes grounded then the supply is no longer isolated and the input would turn on correct ? Can someone explain why they do this ?

 

[Donnchadh]

Hi

I agree I often see suppliers from that part of the world it's often hard to get pnp and I also don't understand it

Donnchadh

 

[keithkyll]

No need for fusing I/O.

 

[Donnchadh]

HI

Ok no need for fusing , but would you still not have to fuse the 24 dc + and I think it makes it harder to trouble shoot but thats only me and maybe that is also down to the way I was trained.

Donnhcadh

 

[osmanmom]

your statement misleading

 

[osmanmom]

give an example or application that using this sinking method are dangerous.

 

[wdd0422]

If a input or output is grounded and the supply is also grounded the input or output will go true\energize and could cause unexpected machine operation.

 

[LadderLogic]

Can someone explain why they do this ?

These days, for historical reasons mostly. In the past, NPN transistors were cheaper than PNP ones. BTW, NPN I/O circuitry seems to be the preference in North America as well.

Your point about false input detection is moot: in a properly designed system a shorted input should never cause an unsafe condition.

 

[osmanmom]

please sketch simple drawing for sinking IO when grounded or touching to earth it become dangerous

 

[wdd0422]

Well , I don't think it's mute because wiring mistakes do happen, and I have in fact seen it happen. If a mistake is made with a PNP it will short. Just seems safer to me

 

[JeffKiper]

I have seen a few machines that the ground positive. So a short to the frame would NOT cause the input see an ON condition.

That I see mainly is US made machines with PNP inputs and 0 volt ground.

 

[Steve Etter]

NPN I/O circuitry seems to be the preference in North America as well.

My experience is just the opposite. With US built machines (those that don't base their designs around non-US supplied controllers) the majority favor PNP.

Your point about false input detection is moot: in a properly designed system a shorted input should never cause an unsafe condition.

While technically I agree that an input short shouldn't cause an "unsafe" condition, but on the other hand the statement was it "could cause unexpected machine operation" which is true. For example, if the machine is waiting for a "part-in-place" signal from a photo-eye as its last bit of logic, a machine could start its next move. I have seen this happen more than once. It may not be unsafe, but it was certainly unexpected.

Because an NPN circuit can operate with a very low current draw, its my belief that this was a major factor in the decision to standardize on the NPN circuit. Reduced power consumption and its associated heat generation are important factors.

 

[wdd0422]

Ok, seems to be the same difference either way. Thanks everybody.

 

[osmanmom]

There a fail safe for digital input/output/analog SIL-1/2/3/4/5.

 

[Steve Etter]

There a fail safe for digital input/output/analog SIL-1/2/3/4/5.

Once again, the original statement, which I agree with, is that unexpected machine operation could result. This has NOTHING to do with SIL.