Ideas on a good PLC to use...

[flyingsparks]

Well here is an update! After much looking (and no luck) to find a cable any cheaper, having asked my boss he has one I can borrow to fit the Telemecanique PLC.

Have now mastered the Zelio software in Ladder mode, and quite like it., Have made a program and simulated and all is working well, with timers and counters too.

Here is another question I do have tho.. looking at capacitive proximity switches, if I use it to send back a 240V signal to the input on the PLC, would I need a NPN or PNP? I can't ever get my head around those two very well!

Cheers All..

 

[bhm1712]

you need PNP

PNP is sourcing the signal i.e putting the signal onto the input
NPN is sinking the signal i.e taking the signal away from the input

Best way to remember is: PNP ends with P for putting, NPN ends with N for not putting.

 

[Spark123]

Worth thinking about which way around fails with least consequence, I usually find PLC inputs tend to fail open.

With a PLC is pretty simple to use either, use N/O contacts or N/C contacts in ladder depending on the type you use.

 

[stillp]

Here is another question I do have tho.. looking at capacitive proximity switches, if I use it to send back a 240V signal to the input on the PLC, would I need a NPN or PNP? I can't ever get my head around those two very well!

Cheers All..

NO!!!

NPN ands PNP proxies are DCdevices, usually >30Volts. You need an AC proximity device, which will usually be 2-wire.

 

[ban-all-sheds]

And here's me thinking those terms referred to the two types of bipolar transistors...

 

[bernardgreen]

People using the terms PNP and NPN instead of Source and Sink for outputs from automation equipment was the bane of my 9 years in factory automation

An output that sources current from 24 volts can have either PNP or NPN or FET type ( P channel and N channel ) devices as the switch between 24 vol rail and the output.

Like wise with a sinking output ( a switch between the output and 0 volt ) the active device can be several type although NPN transistors or darlingtons are the most often used.

As for inputs. very often the device connected to the input pin is a diode in a opto coupler.

 

[stillp]

BAS, they do, amongst other meanings.
Sourcing proximity switches are commonly described as PNP and sinking as NPN, in spite of the fact that either type of bipolar transistor could be used in either type of proxy, as well as the devices mentioned by Bernard and several others. I've even seen relay output switches describes as PNP as well as NPN.
Sorry to bang on, I spent 120 years of my life designing these things!

 

[flyingsparks]

Thanks for your replies. I have been struggling to find a 240V capactive proxy switch for less that £100, but then stumbled across this on ebay which I bought and have now got. It is a XT4 P30 FB262

Data Sheet:

http://www.global-download.schneide...F3E5D0882575780038E422/$File/146067001a55.pdf

You can see the wiring diagram half way down slightly right hand side of the middle. I am now wondering if I can use this as it needs a load connected in series with the blue wire. Is there a way I can put its output into the PLC input? Perhaps having a power resistor there instead of the load then out of that into the PLC input? Or am I screwed?

Untitled

• flyingsparks
• 1 Feb 2012
• 1

 

[flyingsparks]

Or I use the proxy switch to operate a coil of a small relay which then puts 240V on to the PLC input?

 

[bhm1712]

Comment removed due to being garbage even i dont understand

 

[ban-all-sheds]

Were you testiculating?

 

[Spark123]

Not sure about putting a resistor in series with it, the resistor may need to be positioned across the input to the PLC and neutral for it to work.
It depends on the load that the PLC input takes and the prox switch as wether or not you need to have a dummy load or not.

 

[flyingsparks]

gone down the route of the proxy switch energising a relay coil and then putting 240v into the plc that way. Had to get a coil of atleast 2.5W I think it was so as to draw enough current for the proxy switch to operate.