Problem with sensor no reason out signal when power on

Thread Starter

aladjov

Joined Mar 6, 2020
3
Hello, everyone,

I have a photoelectric sensor (6-36 V), PNP, NO+NC and when I power it up for the first time, it generates an output signal with no reason (no object to detect) every time and thus spoils my whole scheme.

What is the reason for this and how to deal with this problem?

Thanks!
 

crutschow

Joined Mar 14, 2008
25,133
Since most of us are not clairvoyant, you'll need to post a complete schematic of the circuit to get a good answer.

In general, you could add a circuit to block the signal during power-up.
 

Reloadron

Joined Jan 15, 2015
5,511
What you need to do is define your project and that means define it in detail. We don't know what your "scheme" actually is and we don't know what your photoelectric cell circuit actually is. The reasons for what is happening could be many and less any circuit diagrams or links there is no way to narrow anything down or make a suggestion.

Ron
 

Thread Starter

aladjov

Joined Mar 6, 2020
3
There are a power supply, a sensor whose output is connected to a relay coil. Its contact system is connected to the load. The circuit is simple, but this "blinking" for a fraction of a second of the sensor when the power turnes on does not trigger the relay when it should (triggers it for a small period each time it is turned on when it is not needed)

This defect also exists when I connect the relay on its own, so it is not a problem in the circuit itself. I hoped there was a way to fix this problem without adding an additional relay, but apparently this is the only solution

Тhank you
 

Reloadron

Joined Jan 15, 2015
5,511
A sensor tells everyone absolutely nothing. Some photoelectric sensors will momentarily output a pulse when power is applied. No relay will energize at power up unless the relay coil is energized. Now if you can't give any part or module numbers this is not going to work.

Ron
 

Thread Starter

aladjov

Joined Mar 6, 2020
3
A sensor tells everyone absolutely nothing. Some photoelectric sensors will momentarily output a pulse when power is applied. No relay will energize at power up unless the relay coil is energized. Now if you can't give any part or module numbers this is not going to work.
sensor: VEMARK, V3F-DS30P3/M
relay: finder 40.52
1.1.jpg
 

Reloadron

Joined Jan 15, 2015
5,511
OK, what is happening is on power up the sensor outputs a false trigger. I have seen it before. Your first option is to ask the manufacturer why it does that and in some projects or applications it can be annoying or a show stopper. Depending on your application you may be able to add some circuitry between the sensor and relay. There is no easy fix that I am aware of.

Ron
 

crutschow

Joined Mar 14, 2008
25,133
this "blinking" for a fraction of a second of the sensor when the power turnes on does not trigger the relay when it should (triggers it for a small period each time it is turned on when it is not needed)
I'm confused.
First you said it's creating a trigger pulse upon power up (which I thought you didn't want) and now you complain that it doesn't trigger the relay upon power up.
So which is it?
What exactly is your problem?
 

MisterBill2

Joined Jan 23, 2018
6,359
Hello, everyone,

I have a photoelectric sensor (6-36 V), PNP, NO+NC and when I power it up for the first time, it generates an output signal with no reason (no object to detect) every time and thus spoils my whole scheme.

What is the reason for this and how to deal with this problem?

Thanks!
Most circuits start out with the power off and none of the capacitors charged. The condition with power off is well defined. Then when power is switched on things change, and after some time period the circuit is in a stable power on state. Without a whole lot of design effort and adding parts there is seldom a instant transition from off state to stable on state.
That is the case in your device.
It is not likely to be simple or easy to alter that situation, and so the obvious solution is for you to have the external circuit ignore that brief output signal. And since you have provided no useful description of the sensor circuit it is not likely that anyone can offer any information on how to change it.
Therefore, the best work-around is to have a delay after your sensor circuit is powered before the circuit it controls is powered. This advice is certain, it is not a best guess based on no information. It is an often used control system function. Of course the fact that you also provide no information at all about the application assures us that nobody can offer a sure fix. This sensor might be triggering a booby trap for law enforcement officers entering a room.
 

MisterBill2

Joined Jan 23, 2018
6,359
Either the scheme requires an instant response after turn on, if the "sensor" senses something, or it does not. If such a truly instant response is important than the obvious solution is to have the sensor powered constantly, and only enable and disable the controlled system, whatever that may be.
But since we have been given no details at all there is no reason to spend any more effort trying to provide a batter answer than has already been provided.
 
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