types of sensor to used for count thing

dr_farnz

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Join Date
Feb 2004
Location
kuala lumpur malaysia
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hi

im having problem to choose what kind of sensor that can be used to count a thing that pass by the conveyor.

the story is like this .
now im doing my final project in my studies.im doing higher national diploma in mechatronic engineering.

my project title is portable belt conveyor.what my problem is when i go to electonics shop to ask for sensor and when i mension to the shop attendent they dont know what is the sensor that i mension to them.

so i need some help due to this problem.
one more thing is im using a plc programming to control the conveyor.
im sure that the sensor also need to be programmed to the plc.

please help me.
thank you
 
As always, the right answer is "It depends".

If your object is metal, you could use a proximity switch, which will open or close contacts or turn a transistor output on or off as the object is detected and then lost. You could use a photo switch to do the same thing. You can either use a retroreflective, where the light is sent out by the switch and reflects back to it if a shiny object is in front of it, or a through beam type (opposed) where the light is transmitted by one device and sensed by another, with the object sensed breaking the beam if it is present.

Go on line and look at the Allen Bradley or Cutler Hammer or Banner Engineering web sites for some information and catalogs.
 
There are numerous types of proximity, photoeye, and limit style switches that will indicate "presence" of an object on a conveyor. Each of the devices can be used with PLCs and you can find them in all voltages.

The size and shape of the object you want to sense, the conveyor speed, and other parameters can dictate the style of switch(s) you purchase. This is pretty simple stuff to figure out.

Good luck.

Wow Tom, you're quick!
 
Since this is a student's theritocal project, I would just simply settle on a through beam photo eye. This would be a seperate transmitter, and reciver on each side of the conveyer.

This will provide a for sure way to count any type of randomly placed objects on a conveyer belt.

A prox sensor would require exact placement, a mechanical switch would requre contact with the object, and a retro-reflective photo beam may pickup ambiant light, or fail to count reflective objects.

Have fun with your project!
 
Here's a few suggestions & applications:

1) Prox switch: Will detect metals (ferrous are best). Use it if you've got a smooth surface that will pass by the SAME spot every time.

2) Capacitive prox: Same as a standard, but will work with more materials (even non-metallic).

3) Ultrasonic: I've never used one, but I suspect it would work like capacitive.

4) Limit switch (MANY styles): The part must touch the switch. Sometimes, simplest is best.

5) Photoeye: There are various types (retroreflective, opposed, diffused, etc.). Your choice will depend on the application. Seek guidance before trying this option.

6) Lasers: Laser/beam sensors are just focused photoeyes. But, there are some benefits to having a tight beam pattern.*

*Once, I was asked to install muting sensors on a light curtain. The sensors chosen by my co-worker were high power retroreflective. He chose them because the distance was 30 feet to the reflector. When the electrician hooked them up he saw "noise" and the muting was behaving strangely. I bought shielded cable at the electrician's request, but it didn't help.

At this point I decided to measure the frequency of the "noise" to see if it was really 60Hz interference. It was 15kHz! Luckily, I'd read some datasheets and realized that 15kHz was the frequency of the photoeyes. Tech support confirmed that at 30 ft. the beam pattern would be 3 FEET WIDE. My photoeyes were blinding each other!!! If I'd thought to use the low-light feature on my video camera I bet that would have been cool to see.

We switched to lasers and our only remaining problem was keeping the beams lined up.

AK
 
Dear farnz,
I agree with the answer above :
for low price ..use limit Sw.
Normally in Automation system use proximity Switch (more expense than limit sw. ) such as
1. Inductive only detect iron (metal or ferrous )
2. Capacitive can detect both metal or non metalic
3. Optical sensor ( can use for long distance ) ,you can buy
laser pointer (cheap) + phototransistor can work as Optical sensor
and low price (but be careful the laser pointer beam danger with your's eye)
Another sensor I am not recommend , depend on your's project cost ,
also ..your's process sequence.

Platootod

sensor in conveyor.jpg
 

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