Infrared sensor for detecting paper

[brunofunchas]

Hi,

I have a printing machine, early 90’s, which has IR sensors on the input that detect the presence of paper. It has a LED and one phototransistor on the same package.

When I put paper over the sensor I still see 12V between the collector and emitter pins. Is it possible that the output of the sensor is in the form of current? Like a digital sensor that for "0" state will be 4mA and for "1" will be 20mA.

The signal 4-20mA is only use in analog sensors?

Does anybody have the typical output wave for the generally used sensors?

Regards,
Bruno

 

[karesz]

Hi Bruno,
I dont know reflex light sensors with current output, but in the life are much things possible...
I think it has a general digital output(more simple for the designer), but it can have only an Phototransistor too, also practically an analog output!
But maybe you can read some coding/type Nr on it?
K.

 

[FvM]

The information you provided is rather vague. Are you sure, that the sensor is using DC (unmodulated) light? Most industrial
open beam light barriers and reflex sensors are actually using modulation. The phototransistor could be a photodiode as well.
You should rather look at the amplifier/detector unit to understand, how the device is operating.

 

[brunofunchas]

Hi,

Thanks for the quick replies.

I do not have the electronic diagram of the board that receives the signal from the sensor. It is a specific sensor that the manufacturers of machine demand to Leuze to put it on the machine. I have a simple block diagram of the input/outputs of the board and the reference on the sensor is from the machine Manufacturer.

The led sends an IR beam to the paper that reflects it to the phototransistor. The voltage on the phototransistor is stable at 12Vdc, whether the paper is or not on top of the sensor.

That is why I am puzzled about this sensor. I did not measure the current from the output so I thought that perhaps the signal is in current and not voltage.

Regards,
Bruno

 

[FvM]

You didn't tell about any issues with the sensor. What are looking for?

 

[brunofunchas]

I have scopemeter and I would like to see examples of other IR sensors output wave.

If it is a square wave oscillating between 12Vdc and 0 Vdc, An ac signal modulating in frequency in function of the distance to the object, etc.

Basically, examples of other sensors to compare with mine.


I have an intermittent problem with the machine, because some times it detects the paper and other it does not.

I would like to know the typical output wave of general used IR sensors (Output in current mode, in frequency, etc..) to see if it similar to the one the one I have.

Regards,
Bruno

 

[brunofunchas]

Hello,

With the scopemeter I could see that the sensor sends a short pulse(12Vdc->0Vdc->12Vdc) when the paper is on top of it.

Thats why when I used the multimeter I had always 12Vdc, I could not see the pulse! One of the sensors had an intermittent problem and did not always sent the pulses.

So if anybody encounters this type of sensor do not assume that the sensor is bad, it is better to check with an oscilloscope.

Topic closed.

Regards,
Bruno

 

[atferrari]

A similar machine to compare values, is it available?

 

[karesz]

Hi Bruno,
Tell me pls; is it not a simple digital (I mean with full supply amplitude as outp. pulse) reflexions sensor with some chopped excitation?
Are you sure, thatit changes the frequency or duty cycle depend of distance to your papers?
I think it is a some square wave supplyed LED for synchron detection & environmental light independent working and it sens only the presence of papers_reflected light or nothing!? Can you agree pls?
I.e. Hamamatshu, Panasonic & Rohm has very good products for such sensor solutions...
How far is the sensor from the sensed papers & is it a specially build component or a usual some modul?
K.

 

[karesz]

Hi Bruno,
I found a Sharp Type(IS471, but I remember similar to snow from & Hamamatsu Honeywell too), maybe your type is same/very similar, or from these family?
http://www.roboticscommunity.com/robotics/Sharp-IS471-Frustration-7944-.htm
Abstandssensor mit IS471: http://www.kreatives-chaos.com/artikel/abstandssensor-mit-is471
K.

 

[brunofunchas]

Hello,

The sensor is quite simple. The output it is not full supply amplitude between states, but only a short pulse. Regardless the distance that the paper passes by, the output is the same. On the output I see a flat line at 12Vdc and when the paper passes it gives a short pulse to ground and up to 12Vdc again.

Regards,
Bruno

Hi Bruno,
Tell me pls; is it not a simple digital (I mean with full supply amplitude as outp. pulse) reflexions sensor with some chopped excitation?
Are you sure, thatit changes the frequency or duty cycle depend of distance to your papers?
I think it is a some square wave supplyed LED for synchron detection & environmental light independent working and it sens only the presence of papers_reflected light or nothing!? Can you agree pls?
I.e. Hamamatshu, Panasonic & Rohm has very good products for such sensor solutions...
How far is the sensor from the sensed papers & is it a specially build component or a usual some modul?
K.

 

[karesz]

Hi, its not clear me; you have only one time these short pulse or periodicallypls?
If periodically, what is frequency/repetitions time & puls width/time pls?
K.

 

[brunofunchas]

Hi,

Just one pulse, even if the paper remains in front of the sensor.

Regards,
Bruno

 

[karesz]

Bruno,
I think its only a normal IR-LED + a detector, maybe built with discrete transistors as a schmittrigger_has in the feedback a time constant_.,..
So can you have a pulse output as simplest solution, and less stabile too(...
I would take some modulated source with integrated selective-sensor, bacouse if you have so a system; your ambient effects are practically eliminated_usually min. up to 10`000 lux_full sunlight!
If you have trouble only with one sensor: maybe its not the same /same wavlength or has some bypass capacitor/transient absorber need!!
Some possible solutions:
https://www.instructables.com/id/A-very-simple-proximity-detector/
https://www.alibaba.com/product-free/105652805/IR_Sensor.html
I would take these or similar IR sensor, then the modulation(chopping) makes it sure for disturbing noise/emi signals & if the output has the 33-36KHz pulses, triggern an monostabil coupled 555 for the same pulsewidth what you have yet!
LM555 can work from 12V too, you must make only some small PCB/experiment board...
K.