I have an application where I am trying to detect grit media level (anywhere from "sand" to aluminum powder) in a 55 gallon metal drum with a metal lid. This is a waste drum, so I'm looking for a 90% and 99% full signal to alert the operator that it's time to swap the drum with an empty one.
Right now, I'm using 2 shielded 4mm range capacitive proximity switches. They are hanging from the lid so that 1 trips at about 90% and the other at about 99% full.
This scenario works relatively well, except that:
I've tried to address those issues by purchasing 2 5-40mm adjustable range N.C./N.O. non-shielded capacitive proximity switches. The goal was to mount both of them in the lid in a way they wouldn't need to be taken out when changing the drum. Then take advantage of the adjustable range to set one to trigger at 90% and the other at 99% and set them to N.C. to make them fail-safe.
I tested this about an hour ago. I purposefully got the proximity switch tip "dirty" with grit media and mounted it on a steel plate to mimick the lid environment. Then I held the assembly over a partially filled drum and by the time I zeroed the proximity switch, I didn't have enough sensitivity range left to make the switch even remotely reliable.
I don't want to keep buying proximity switches just to try something else. I admit, I probably should try to get a shielded proximity switch and that might improve my chances to succeed, but at this point, I'd like a little guidance from the experts here who have much more experience than I using level sensing devices under a variety of applications.
I already know from previous research that sonar is not good in powder. Radar is prohibitively expensive for this application. Optical would probably fare even worse than capacitive proximity switch due to the high "dust" environment. Inductive relies on conductivity - OK for aluminum, but not OK for "sand".
We've ruled out using scales to weight the barrel or anything of that nature.
As you can tell, I need some advice here. Thanks in advance.
Regards - AMS2750
Right now, I'm using 2 shielded 4mm range capacitive proximity switches. They are hanging from the lid so that 1 trips at about 90% and the other at about 99% full.
This scenario works relatively well, except that:
- We've had a couple of false positives due to the sensor getting dirty from the grit media swirling around in the drum.
- This setup requires the proximity switches to hang in the drum, so I have to pull the hanging bracket out of the lid every time I change the drum because the lid can't really be lifted off more than an inch at best to slide the drums in and out.
- The proximity switches are N.O., so a disconnected cable, etc... will make the system think everything is OK.
- The "hanging" system is rather cumbersome
I've tried to address those issues by purchasing 2 5-40mm adjustable range N.C./N.O. non-shielded capacitive proximity switches. The goal was to mount both of them in the lid in a way they wouldn't need to be taken out when changing the drum. Then take advantage of the adjustable range to set one to trigger at 90% and the other at 99% and set them to N.C. to make them fail-safe.
I tested this about an hour ago. I purposefully got the proximity switch tip "dirty" with grit media and mounted it on a steel plate to mimick the lid environment. Then I held the assembly over a partially filled drum and by the time I zeroed the proximity switch, I didn't have enough sensitivity range left to make the switch even remotely reliable.
I don't want to keep buying proximity switches just to try something else. I admit, I probably should try to get a shielded proximity switch and that might improve my chances to succeed, but at this point, I'd like a little guidance from the experts here who have much more experience than I using level sensing devices under a variety of applications.
I already know from previous research that sonar is not good in powder. Radar is prohibitively expensive for this application. Optical would probably fare even worse than capacitive proximity switch due to the high "dust" environment. Inductive relies on conductivity - OK for aluminum, but not OK for "sand".
We've ruled out using scales to weight the barrel or anything of that nature.
As you can tell, I need some advice here. Thanks in advance.
Regards - AMS2750