Sensors Measuring powder flow.

[atifplus]

We have a photo sensor to monitor the flow of starch but coz of the dusty environment the sensor is generating teh fales alarm. Putting the sheilding will just move the problem from keep the lens clean to keeping the shield clean.

Any suggestion what other sensors I could use. I am just starting my search about sensor
I am wide open to suggestion

Thanks in advance
Here is the figure of setup

 

[Tharon]

A small air line with a valve to control a blow off every 'x' cycles or minutes. Pulse it from two (or more) different directions if you feel it will help to remove more build up.

This will help stop any accumulation.

 

[atifplus]

We have a shielding designed for the sensor that was constanly purging air to keep the lens clean but it isn't helping much. I am still looking into the problem. It could be moisture that is causing the starch to stuck on the lens. Operator have to go walk x meters to clean that lens often .Maybe Using the laser sensor will eliminate this problem.

plz post if any one has worked with this sort of arrangement

 

[Tharon]

Constantly blowing air and pulsing air from different directions yeild different results.

If you constantly blow on the starch, it could still build up, where as pulsing from different directions aggitates the starch more, helping remove more of it. I use multi-direction short bursts of air to remove aluminum chips from drills and other machining operations.

As for a laser being less susceptable to the build up, I don't think it would. I have a few places that use lasers to detect things passing through shoots, and they still get greasey build up on them that stops them from working properly.

I just think that a change in the way you blow off the eye will be an easy possible solution. Another thing to look at is how the eye is positioned, if it has a "lip" that the starch is building up on, try to position it facing at a downward angle to remove any ledge the dust may be collecting on.

Just ideas.

 

[MartB]

Mount the sensor pointing down at an angle of greater than 30 degrees, I've found this solution has worked in 'reducing' false errors in the past.
However, I've yet to see a system that completely eliminates the occasional false error (i.e. less than once a month on a 24/7 operation).

 

[rsdoran]

Using air may be the problem, have you checked the moisture content of the air at the blow? May want to use a filtration or drying system at the blow point to help remove the moisture content.

Take a look at the FRL and Drying systems offered by Numatics as an example: http://www.numatics.com/

Another option may be to use a weight scale and/or rotary feeder.

 

[atifplus]

Wow some really good ideas.



I really like the technique of putting the sensor facing at some downward angle. Also, what sorts of arrangement u have for the pulsing air? Some info would be really helpful.

I will design a block that will make the air pass though lots of small nozzles aiming at different angle rather than one nozzle. Something like fig below

The whole environment is so dusty like foggy . Therefore I will design a shield to prevent the surrounding dust from entering in. the only thing left to worry about is dust entering from that hole and hopefully the pulsing air will take care of it





Thanks a lot guys for some nice ideas



Info about the pulsing air will be really helpful J



Atif

 

[atifplus]

Humm good observation.. I will look at the air supply to check if there is any moisture in it.


Thanks for the pointing it out.

 

[atifplus]

aaa we have an accurate weighing scale but hooking it up to PLC will be a bit expensive I believe.
I am concenrating more on improving the sensor

 

[Tharon]

Make sure to look into rsdoran's suggestion, about the moisture level of the air.

As for the pulsing, Usually I have an event, like the end of a cycle, start a timer. Then I use LIM or GRT/LES Instructions to compare the accumulator value of that timer, and turn out the output to the valve.

Say I wanted to blow air, first one way, then the other, then the first way again, then the other way one last time. Left, Right, Left, Right, kind of thing. I'd just make a 2000 ms timer, and between 1 and 500, energize left, between 501 and 1000 energize right, 1001 and 1500 left again, and 1501 to 2000 would energize the right again. Times can be easily adjusted, and we usually use around 80-100 PSI, depending on what the machine is set to.

The number of valves needed depends on the number of directions you want to blow in at seperate times.


Now, this will help with the problem of build up on the lens, but if your problem is the material floating in the air... this might make it worse

 

[rsdoran]

aaa we have an accurate weighing scale but hooking it up to PLC will be a bit expensive I believe.
I am concenrating more on improving the sensor

Not knowing the details of the application I have no idea what expenses may be involved but cost is not always the concern, reliability of accruate feeding may save on that cost in the long run.

I have worked with AccuRate feeders and definitely think they are good systems. I worked for a company in 96 that automated their lines and most of their feeders were AccuRate and not at all difficult to incorporate into the AB PLC/5 system they used.

The product used all dry material, gypsum, sand, clay, carbon, ground paper, and a few other chemicals I do not remember.

That said I would definitely look at what may be involved using the AccuRate system.

 

[atifplus]

hahaahah ya i went to see the area in the morning (when i first posted my questions) maybe i was too sleepy to notice the dusty environment but after visiting the place at 10ish i am like waaah the whole place is dusty so covering for the whole sensor is a must and oh awesome using the valves ya so using the valves i can do that sounds so promising


thank you thank you for all the good info

Atif

 

[atifplus]

Thanks Rsdoran I will do a research on both the methods and post it here to see if anyone could point out any flaws in my design.

Thanks for the motivation

 

[rsdoran]

Another thought

I know air is already there BUT the more you use the more demand you put on the system. Whether its pulsing air or an air leak it adds to the demand of the system; which in effect causes more power to be used.

An example of sorts, others can offer more precise information, a simple air leak or small air line (even pulsed) can use 5HP (3.7KW). Calculating a years use of the power involved may show an ROI for another method.

 

[OkiePC]

We had a rep from Sick optic look into a spray booth application in a tire plant (green tire lining cement). He said they had a thru-beam laser eye that would tolerate an incredible amount of build up. We never pursued it though, but you might call a representative from Sick and some of the other sensor companies and see if they have a better device for you.