False triggers

Need some feedback here. I am using a 4wire prox inductive sensor on one of the system my company builds, but I am using only three of the wires. The sensor is a NPN type, and I am using 12V DC for power. The problem is I am experiencing consistent false triggers before metal target pass the sensor.What could be causing this problem. Could it be grounding fault?

You didn't mention the brand or part number of the prox, making it difficult to answer. There is 3 types of 4 wire prox's. Complimentary, NPN/PNP, and Configurable NC/NO. If yours is the configurable type, then the 4th wire must be connected to + or - to set it to NO or NC output. If you leave this type floating, that will give you false triggers because it toggling the output type. See page 4 of this document:

[size=-1]www.automationdirect.com/static/specs/proxterms.pdf


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I usually put a timer on all the digital inputs. Sometimes a 1/10th of second timer will stop false triggers if the problem is noise, and it will stop chatter from dry contacts from causing problems. If the timer is not needed just leave the preset at zero. When I get to startup I don't have to add these in, I just adjust the preset, saving time. Sounds like wiring could be the issue here though.

Keithkyll:This is a 4-wire NPN turck sensor with complementary outputs. NO is being used for switching, and NC connection is not used.

Maybe the supply voltage drops below 10Vdc or is carrying lots of noise...Turck (and others) prox switches become unreliable then. Try using a cap (100µF should do it) over the supply, as close as possible to (or even inside) the prox.

Does the output control LED on the prox actually light up? Or perhaps the input (or the wiring) itself is causing the extra triggering.

Specs on detecting distance mention that the object should be grounded. Leaving objects ungrounded only influences maximum detection distance.

mosamB said:

Need some feedback here. I am using a 4wire prox inductive sensor on one of the system my company builds, but I am using only three of the wires. The sensor is a NPN type, and I am using 12V DC for power. The problem is I am experiencing consistent false triggers before metal target pass the sensor.What could be causing this problem. Could it be grounding fault?

Click to expand...

Check the sensing range & sensitivity of your sensor

check the sensing range of the prox. it may be on the edge also cap off the fourth wire