pnp Proximity switch

[moose man]

sorry to be a pain

can not get me head round how these work haveing a bad day

could somebody explain what the difference

is between pnp npn type and how to test the output

thank moose

 

[M107]

I assume you are on about transistor switching?

To test a PnP transistor

set multimeter to DIODE test with red lead in V / ohms terminal & black lead in common terminal of the meter.

connect meter leads to transistor;

Black to base

Red to emitter & then collector

You should get a reading from both positions, you've prooved forward biased.

Reverse the leads at the transistor;

Red to base

Black to emitter & then collector

You should get O/C prooving no conductivity between pn junctions.

Take a resistance reading between emitter & collector to proove no S/C.

To test a NpN transistor;

Set the meter up in same way.

Red lead to base

Black lead to emitter & then collector

You should get a reading from both positions, you've prooved forward biased.

Reverse the lead connections on the transistor & as before you need O/C

Resistance test between emitter & collector should give O/C.

Take a look at this site to explain the PNP & NPN & how they are used for switching or amplifying.....

http://www.electronics-tutorials.ws/transistor/tran_2.html

http://www.electronics-tutorials.ws/transistor/tran_3.html

http://www.electronics-tutorials.ws/transistor/tran_4.html

Far easier than me trying to explain base biasing voltage controlls the collector/emitter.

Gotta go have a few quotes to look at tonight.

 

[Sidewinder]

M107,

Close, these are also descriptions of proximity switch functions.

You can't directly test the transistors in these switches, nor can they be effectively tested without power & a load.

Best way in circuit machine safe put a ferrous load in the detection zone & check the output led. This depends whether it is inductive or capacitive though.

Colour codes used to be manuf' dependent.

Will have +, -, gnd, possibly 1 no &/or 1nc pair, or just a no or nc output.

Try the Schneider group or ifm website.

 

[oldtimespark]

PNP sensor switches on the positive rail of the power supply.

NPN sensor switches on the negative rail of the power supply..

I have underlined the first and last letters of the sensor output types use

This as a memory aid I.E two P positive switching two N negative switching

 

[moose man]

PNP sensor switches on the positive rail of the power supply.NPN sensor switches on the negative rail of the power supply..

I have underlined the first and last letters of the sensor output types use

This as a memory aid I.E two P positive switching two N negative switching

Thanks mate that a great easy to understand

the switch is tool protection on a power press

may be get my head around it now what is the best way test the out put side if the diode is lit but no signal

 

[oldtimespark]

Here is a link have a look also had to edit drawing one led orientation wrong see new drawing

Moose Man please could you please edit the quote in your post to the new drawing

 

[oldtimespark]

Here is a link to an article on machine control systems

 

[M107]

Thanks sidewinder & oldtime I have also learnt something new.

 

[roys]

Good read that was on the machine control systems.

 

[Sidewinder]

One thing OldTime,

We used to use PNP & NPN proximities, with inbuilt electronics.

There is no doubt the type you describe are the most common, however there are others around, though they may have been made especially for us, it was a while ago since I used them now.

We definitely had volt free no & nc contacts in some and others that "worked" as an no & nc.

We also had other switches that "looked" like proximities and had inbuilt circuitry to act as a rotation detector, and others that were proximities that we had to feed the outputs into a box of tricks to act as a rotation sensor.

One point being, is that some machine machine makers will sometimes use trick kit to achieve their aims, which, "looks" like normal, but may not be!

One final comment on the mrplc site linked by OldTime (Thanks BTW). It is a Canadian site, much of the do's and don'ts in there are covered by the Low Voltage, and Machinery Directive and their attendant standards in the UK, such as BS EN 60204-1 I keep harping on about.

However, the points there are well worth reading and noting. One caveat immediately springs to mind. 110V a.c. is OK for control wiring especially over LONG distances, think of the volt drop in small control wiring if you are running a large contactor coil current for a few hundred metres!

However, 24V d.c. where possible.

This is where you come across SELV, FELV & PELV on machinery systems.

HTH

 

[oldtimespark]

Your comments on the site linked to are well founded.

The parts in the article that was of most interest to me was the use of NPN output stage sensor where the negative rail is connected to ground.

All control system should be wired to the relevant standards that prevail in the country of use.

As to the point of N/O or N/C contacts light or dark sensing this is very pertinent.

One make of sensor that is in use where I work can be used for NPN, PNP, N/C or N/O contacts.

Here is a link to there product finder page.