help with choosing a sensor

[who716]

My boss was talking to me the other day about wanting to install a sensor in his shop that will turn on a light once the sawdust bin was full, knowing that I was in robotics he handed me the job of figuring it out. unfortunately sensors were not my thing when I was on the team. basically im looking for some sensor ideas, my fist thought was a weight or density sensor. any other ideas.

[EricH]

A rangefinder, or several of them, mounted above the bin. When all (or one) of them show below X distance, light the light. Might work really well if the bin could be somehow shaken to settle the dust.

Weight sensor would work well, and simply--provided that you know the weight of a full bin. ("Load Cell" is what you'd be looking for.)

Density sensors don't really exist that I'm aware of. You could rig one with a weight sensor on a known-volume bin.

Depending on how the sawdust enters the bin, it might be possible to rig a flow-rate sensor on the entry/exit route(s) and run some calculations.

[Alan Anderson]

You could use an optical proximity sensor (Banner or similar) mounted at a certain level, looking sideways, to detect when the pile of sawdust gets high enough to trip it. If you did that I'd suggest mounting it inside a transparent tube that hangs down into the bin.

[Jon Stratis]

What about recording the run time of the machines that contribute to the saw dust? You can probably figure out an average rate of dust creation per machine while the machine is in use, sum that up over all the machines over time, and include a safety buffer and you're all set.

Of course, using something like a weight or proximity sensor will probably be easier... just not as fun!

[MrRoboSteve]

Another option is to create a small outlet near the full mark of the bin, with a small door that is blown open when the dust collector is on. Put a limit switch on the door.

When the dust collector is operating AND the limit switch is not tripped, the bin is full.

Advantage of this (although less fun) is that it can be done entirely at 110v.

Then connect this, and you're set.

[who716]

thank you for the ideas, the dust collector will be releasing the dust into the bin from the top. That is why I think some of the proximity sensors and what not might not work because it could be getting tripped quite often by the dust simply falling past it. But what Alan said might work especially if I put it at an angle with a semi shield to prevent dust from covering its path.

[Tungrus]

If the dust collector is seated load cell will be a good option. Optical proximity sensor would work if it is mounted with a canopy and possibly a protection shield to prevent dust flying across the sensor. If it is possible to have a glass window IR sensor may be an option.

Whatever sensor you use, use couple of them (depending on the size of dust collector) ad use in combination.

[nathannfm]

I know this might require some more complicated electronics but I would recommend that whichever sensor you pick that you rig it to trip early (like 90% full) but put a few minute delay on the "full" signal. From when the sensor trips to when the "full" signal is lit the sensor should stay tripped, if it doesn't stay tripped the timer should reset. This should prevent false alarms from flying dust or vibration.

[Mark McLeod]

For such a dusty enclosure I'd suggest testing with an ultrasonic sensor rather than a photoelectric one.

[headlight]

If you go with an optical sensor I would consider putting them in the path of the airflow so hopefully the dust gets blown off. Remember, you will probably have dust sticking to the plastic due to static cling, so just angling it might not be enough.

I would personally recommend the weight sensor. Forget the load cell, it doesn't have to be fancy, just tip one of the feet up and put some springs under it with a mechanical limit switch, adjust the springs until the switch makes when the bin is approximately full. It won't require the use of a micro controller or other electronics, and will be easy for other people to adjust and trouble shoot if you're not there. Additionally you can probably make most of it out of wood, which I assume is what the shop does.

[Mr V]

You are on the right track with either measuring the weight or density. Both of those sensors can be located outside of the bin so they aren't affected by the dust in motion or a static charge building up a film of dust on the sensor's lens.

The easiest would likely be the density sensor since you can buy a complete ready to do solution relatively cheaply, though it might not be effective if the bin is made of metal.

I'd recommend the Franklin ProSensor 710 since it will act as a bar graph and show you as your are approaching full before you get there. A little modification to it would be best, replace the momentary contact switch with a standard on-off switch and wire a battery eliminator in so you don't have to replace the batteries all the time.

If you want to go a little cheaper then you could go with a basic stud finder which can be had for under $20 though I'd still recommend the switch and power source modification

[Chadfrom308]

You can use an arduino and a limit switch/ proximity sensor/ ir sensor.

They are easy to program and you can plug a phone charger into them and they are good to go!