Can i wire 3 Prox. Sensor in Series to 1 input?

[Akif KC 0]

Can I wire 3  Prox. Sensor in Series to 1 input? Can someone please assist me? Thanks.

[Armadillo852 25]

Yes, we do this a lot.

What we do is take the first sensor and wire up power and common. Then we take the input (Usually the black wire), that would go to the PLC, and use that for the +power on the next sensor. Repeat that for the third sensor. Then use that input back to the plc.

So basically:

First sensor:

+24Vdc-, -Vdc, Input

 

Second Sensor:

Input from first sensor(+24Vdc), -24Vdc, Input

 

Third Sensor:

Input from second sensor (+24Vdc), -24Vdc, input back to PLC...

[BITS N BYTES 66]

https://rockwellautomation.custhelp.com/ci/fattach/get/165009/0/filename/Connection+of+sensors+in+series+and+parallel.pdf

[Michael Lloyd 85]

For me a "proximity sensor" can also be a vibration probe (Solar turbine or turbo expander for instance) and the answer to that would be NO. :) if it's a discrete then the answer is above this.

Edited 17 Apr 2017 by Michael Lloyd

[Akif KC 0]

Wow, Thanks Armadillo. Makes complete sense. Appreciate for your description. :)

Thanks guys. :)

[kaiser_will 65]

Pay attention to BITS N BYTES' link.  Be aware of the PLC's inputs and the sensors specification (NPN or PNP).  We typically have only NPN sensors and inputs; PNP throws our electricians for a loop.

[panic mode 246]

also be careful with number of sensors... few are ok but ... unlike push buttons and switches, electronic sensors have bigger voltage drop. in other words output becomes smaller and smaller. your input will have some limit (12V or so) that need to be considered.

[Akif KC 0]

Okay, so I should be worried more about the voltage drop? How about if I want to go in parallel connection? I think I  have to worry more about current consumption if I am going in parallel, right???

[panic mode 246]

yes, for series connection you need to check specs. most sensors specs state voltage drop as something like "<2.5V", for example:

https://cdn.automationdirect.com/static/specs/prox12mmpb.pdf

in reality, voltage drop depends on current draw so smaller current smaller drop.

current consumption will not change much regardless if sensors are in parallel or series (they usually draw very little anyway) but the load current does not increase. diodes shown in AB document are a good idea for preventing backfeeding. Most sensors on the market are using open collector output so omitting diode will (usually) not be an issue but smart designer would check datasheet as more and more sensors have totem-pole or push-pull output stage. paralleling sensors does not mean you can use larger load (lower resistance) since bottleneck would still be a single sensor. Btw diodes have voltage drop too (everything does).