PLC transistor and relay output

[Aaron Hao]

Hello, I want to ask what's the difference between relay and transistor as PLC output ? and what are the effects of npn pnp transistor to the PLc ?

Thank you very much

 

[MasterBlaster]

The relay type modules allow you to switch higher currents than transistor outputs, and because each 'output' is actually a set of mechanical contacts, you can have different voltages passing through each "output'.

Transistor outputs are limited to lower currents, and each module is designed for different AC and DC configurations. And, depending upon what you are controlling, the fact that transistor outputs never really "open", but rather "go low", the leakage current can become an issue. When it does, interposing relays are usually the cure. Another 'cure' can be bleeder resistors, and I've even used neon lights as bleeders.

This is the short version of the answer to your question. If inadequate, please ask for additional info.

 

[balash]

i would just add that because transistor doesn't have mechanical contacts it wear significantly less which means it can handle much more switchings during its use.

 

[Tom Jenkins]

As indicated above, relay outputs usually allow mixing different voltages and AC or DC on the same output card. You have to look at the commons - sometimes several outputs share a common and therefore have to switch the same voltage. Relay outputs generally have higher current ratings. Relay outputs are not suited to very rapid cycling.

Transistor outputs are DC, usually 24 VDC. They cannot usually handle high currents, and the outputs on a single output card often share the same common, meaning they must switch the same DC power source. They can handle very rapid cycling and so are useful for pulse outputs.

Triacs are solid state outputs used to switch AC. They are otherwise very similar to transistor outputs.

 

[jvdcande]

Too bad people involved in automation have to ask this kind of very basic questions. We propose this as one of the eliminating questions to people selecting new employees. I guess nowadays the majority of people looking for this kind of jobs are IT oriented.

Regards,

 

[Aaron Hao]

Hi all, thanks for the info. Much appreciated.

 

[shooter]

well jean this is a question everybody gets in his first exam. and he is in for one month only.
so give him a chance.
btw i understood verbrugge is coming to zeebrugge (big company in vlissingen)