WTH...sinking sensors, are you KIDDING ME!

Miguels244 · Jul 9, 2014

EE draws up a print for an interface circuit.
Turns out the sensors are SINKING, who besides the Japanese still uses sinking sensors.
Now We need to put relays in the interface circuit.
ARGH.

edti:Wrong forum, should be in Robotics/Automation.

lwalker · Jul 11, 2014

You mean sinking as in the sensor output is a low-side switch to ground? If so, what's wrong with that?

Miguels244 · Jul 12, 2014

Yep, like that.
The problem is that almost NO ONE uses them and they are wired differently.
Also, your PLC needs to be set able to take the signal, you need to buy oddball cards.

So...when you see a sensor on a machine you are trying to integrate it can take an hour to figure out why it's not talking.

motion guru · Jul 12, 2014

That is odd, we use almost exclusively NPN sinking sensors, especially with motion systems where we need a crisp registration input. Nearly 100% of the registration inputs have pull-up resistors specifically for this purpose.

Now if you are using bang-bang motion with positioning by proxes into standard PLC I/O . . . Yes, PNP sourcing sensors make more sense.

Overall, NPN sinking sensors are dramatically more noise immune and can often be specified with better than 100usec response times. I won't tolerate a sourcing sensor on our machines if it is motion related.

Miguels244 · Jul 12, 2014

motion guru said:
That is odd, we use almost exclusively NPN sinking sensors, especially with motion systems where we need a crisp registration input. Nearly 100% of the registration inputs have pull-up resistors specifically for this purpose.

Now if you are using bang-bang motion with positioning by proxes into standard PLC I/O . . . Yes, PNP sourcing sensors make more sense.

Overall, NPN sinking sensors are dramatically more noise immune and can often be specified with better than 100usec response times. I won't tolerate a sourcing sensor on our machines if it is motion related.

True...not if you need speed.
This is a low grease flag on a Graco pump though.

smcmains · Aug 28, 2015

I like NPN sensors for our applications, most of the time our guys change out sensors without tagging out a machine (I know....I know). If they happen to drop the "signal" wire or it gets a bare spot on the wire, there is no concern about it shorting out against the machine (as it's a ground or 0V).

WILLEO6709 · Aug 28, 2015

Miguels244 said:
Now We need to put relays in the interface circuit.
ARG

Ignore the EE and put in what you want........

Miguels244 · Aug 28, 2015

smcmains said:
I like NPN sensors for our applications, most of the time our guys change out sensors without tagging out a machine (I know....I know). If they happen to drop the "signal" wire or it gets a bare spot on the wire, there is no concern about it shorting out against the machine (as it's a ground or 0V).

This is exactly why PNP/Sourcing sensors are preferred.

cncbeastmaster · Aug 28, 2015

hi motion guru, I know it has been a long time since you wrote, I am just getting into your area of study, I have done some sensor T-shooting and replacing on direct logic 205 PLC, I would like to learn more about automation especially in the home and I wonder if you could recommend any DIY course ware? thank you in advance,

thermite · Aug 29, 2015

Miguels244 said:
This is exactly why PNP/Sourcing sensors are preferred.

Fecks sake, Miguel. There is no "one-true-religion" in electron-pushing. Sometimes one needs differential circuitry, quadrature, polyphase, or encoded packets with error-detection and correction to deal with an environment.

Just broaden your knowledge base, submerge the prejudices, and use what best suits the need actually at hand.

Prior Pilgrim as designed it may be an Idjut by your metrics, but never forget that he was a successful enough Idjut as to have gotten the sucker through test and into volume production .....or you wouldn't be looking at it anyway, so..

JFDWT

Bill

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