Polarity question,trying to understand a prox switch issue

[Skiroy]

Okay Im designing a an alert system for a robot. To make a long story short Im tryng to understand how this 2 wire switch works

http://www.automationdirect.com/adc/Shopping/Catalog/Sensors_-z-_Encoders/Inductive_Proximity_Sensors_-z-_Proximity_Switches/18mm_Round_(AK_-z-_VK1_-z-_PKW_-z-_PBK_Series)/Standard_Sensing_Distance_(AK1_-z-_PBK_Series)/AK1-A0-2H

First let me ask this. I have attached a Jpeg. If the polarity is such on the first figure at the Load 1, am I correct to assume how the polarity is when you add Load 2?



I am asking this because I have a negative(COM) connection coming out of a PLC that goes to the robot. It is a handshake signal that tells the robot to come and get a part. I am trying to put this switch in series with it to stop the robot from getting the part unless there is a part present at the switch. The switch has a LED on it.

This got me to thinking. If this switch is in series with a negative wire how can it light up unless there is a negative and positive connection? I know this is elementary electronics question but I normally just replace parts not design them. The only way I can think this works is if my diagram is correct when adding L2 or Load 2.


Finally, the PDf spec sheet for this switch says its load current is 0-100Ma. So does that mean I can run this switch in series before a photo sensor that is rated at an Output Max of 250Ma? Or does load current mean thats the 2 wire switches current consumption? If so what in the specs sheet tells me that is can handle other devices in series with it that draw more than 100Ma of current?

 

[Skiroy]

bump

 

[Skiroy]

bump

 

[Skiroy]

I know this is a stupid question but Im in a situation right now I need to get my self out of at work. ASAP.Please help.

 

[sahib]

I complained in your  other thread for lack of info  but now I know what you are trying to do.

That sensor is not two wire. There are three and four wire types. You should be using 3 wire types.
Connections are +V, 0V common and output. There are two types of outputs. NPN and PNP. NPN sinks current and PNP sources. Imagine you are using an NPN output type (which I advice for your application), controlling a relay and using 12VDC supply.

Connecting the supply voltage is the same on both types. +12VDC goes to +V and 0V goes to 0V common. +12VDC connects to one end of the relay coil. The other end of the relay coil connects to the output. Normally the relay is off. When the sensor detects it turns the output transistor on. Transistor conducts and connects the relay to OV common. The relay turns on.

If the output of the sensor is rated at 100mA this means that the maximum currnet that the output transistor (NPN) can handle is 100mA.

Why are you using  inductive sensor? Why not IR or even Red LED types?

Neither your text nor your schematics make any sense in your other thread. Perhaps you should just delete it and continue here.

And explain what your robotic system is and the sequence of operation.

 

[kazper]

Most PLC inputs are Sinking or Sourcing, you can tell what you have by card part number or how it's wired.

If you have +VCC on the Common terminal and your switching the DC - then it's Sourcing.
If you have DC- on the Common terminal an your switching the +VCC then it's Sinking. I see sinking most of the time in industrial applications.

http://www.automationdirect.com/static/specs/sinksource.pdf


You are correct it's 2 wires as shown by cross referencing your part # to the messy spec sheet. For the part you listed, use wiring diagram #2 then from your sinking or sourcing information wire according to the drawing. Just a note the L or Load is the PLC input.
http://www.automationdirect.com/static/specs/prox18mmak.pdf


Next go skip Automation direct and use the new Allen Bradley Micro 800 PLC line, uses a USB cable and the software is free. It's a very powerful system for what little the items cost. I also prefer IFM effector switches, I'm not very impressed with automation direct stuff.

 

[kazper]

This got me to thinking. If this switch is in series with a negative wire how can it light up unless there is a negative and positive connection?

Finally, the PDf spec sheet for this switch says its load current is 0-100Ma.

Once it's wired correctly with something to trigger it it's like a series loop and it lights the LED because it has a complete path for current flow.

Your L or Load  has to be under 100Ma... if you drive the PLC input with it it's probably only a few mA .  Then you can use a PLC output to handle the heavy lifting most likely up to 10A but I would use a interposing relay for more than 2.5A just because there cheaper than the card.. It's also common practices to go straight to PLC then use an output for signaling even if it's just retransmission of the signal but I have seen some use a relay before PLC. and this is more application specific.

I have experience with them in Industrial applications which were done with custom provided computer/electronics control or PLC logic for control which looks like what your doing here.

Is this for a class?