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Postion sensor for dumpster with induction loop - any experiences?

Postion sensor for dumpster with induction loop - any experiences?

We need to build a system that detects if a dumpster is standing at it'S place (so the conveyor belt knows when to fill it and when not).

Classical induction sensors have a range of 20-30mm, we are not sure the truck driver will always position the dumpsters that close to anything. A positioning system is there (steel rails in ground) but not exact enough.

Installing a sensor in the concrete platform the containers will stand on introduces new headaches so i thought about sensor that are made to be installed on/in the ground and arrived at an inuction loop, as found in trafic control. The loop wil be placed in concrete, with (some) rebar underneath. We are favoring a system where a prepared plasitc pipe with the cable inside is pured into the concrete. I've reached out to suppliers and am waiting for a reply, so far no one has experience with this specific application. Hence my questions:

will it work? the dumpster floor will be far closer than a car, but also have far less mass - basically a few mm of metal. Is this enough?

For signal, I want (after configuration) a binary signal, nothing more (traffic control systems seem to be really competent up to identifying passing cars. Not needed by me!).
What else should I think of?

RE: Postion sensor for dumpster with induction loop - any experiences?

I suggest that you read:, particularly section 5 regarding rebar location.

Note that standard traffic control inductive sensing can usually detect motorcycles.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!
FAQ731-376: Forum Policies forum1529: Translation Assistance for Engineers

RE: Postion sensor for dumpster with induction loop - any experiences?

Helpful. Some suppliers state that the cable should not be directly above single rebar bars, needs some horizontal distance - see images here: (left image wrong installation, right image correct)

RE: Postion sensor for dumpster with induction loop - any experiences?

Hi Martin,
A vehicle (inductive) detection-loop, and associated relay, should work fine. I have used Sarasota units before (for gate control). However, the rebar might be an issue. You should talk to the OEMs to see what, if any, rebar their equipment can tolerate.
Another strategy is to use photo electric controllers to determine if a dumpster is in place. Note: it may take more than one PEC to guarantee that the dumpster is in the correct position. I prefer this option as all of the hardware is above grade and rebar won't be an issue.

RE: Postion sensor for dumpster with induction loop - any experiences?

I predict complete failure of an 'inductive loop' scheme. Lousy. Will cause you no end of headaches and not provide a location more accurate than spitting distance. If you want the dumpsters positioned then use a position sensor. There are many. Ultrasonic can get you within an inch. Or use classic interruption light beam sensors to shoot across the dumpster position. They're modulated and have little difficulty with ambient light unless you work really hard to perfectly align them with the sun. Cheaper yet are whisker switches which are simple microswitches with a spring and long rod. Put them where the dumpster shoves them when in place. Hopefully you're also providing a signal to the dumpster delivery folks to tell them "perfect" no farther, no shorter. It could be a light or a beep.

Keith Cress
kcress -

RE: Postion sensor for dumpster with induction loop - any experiences?

How about just using physical stops with suitable entrance ramps so the the dumpster is forced into the correct position as the driver approaches. One example would be two or more small pyramids on the ground that mate with matching sockets on the dumpster. As long as the dumpster is within a foot of the correct position, it will slide into exact position as it is lowered. This works really well for stacking warehouse storage bins and shipping containers, and gives the driver visual feedback. You may still want a presence sensor for your control system.

RE: Postion sensor for dumpster with induction loop - any experiences?

Vision sensors are the new paradigm for something like this. You place the dumpster in place in the field of view of the sensor, have it "learn" the proper image it needs to see, program acceptable tolerances and you are done. If the dumpster is not in the right place or position, or they use the wrong dumpster that is a different shape, or something is in the way, the vision system disables the conveyor feeding it. You can even get some that will recognize color.
They are typically made for much higher resolution / smaller parts and faster speed than what you need, but I have used them for locating large vegetable hoppers for packing machinery, same basic principle. Everything else we tried had problems over time, this was extremely reliable. We used one from Balluff, but there are lots of them available now.

"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

RE: Postion sensor for dumpster with induction loop - any experiences?

The customer uses this specific container type:

These are lowered from above.
so we can't use rails or the etup with the pyramids used above. This means our positioning is not very accurate, which is why I exclude most classical inducion switches.

I've since talked to suppliers, apparantly they can handle rebar since (these systems are used in multi-storey parking garages).

The vision sensor is a fascinating possibility, probably too much novelty to convince my boss and our customer but I will read up on it for the next project.

RE: Postion sensor for dumpster with induction loop - any experiences?

How about one or two pivoted rods or cross bars with limit switches? The driver would have to position the skip so as to activate the limit switches. Sensors could be used for non-contact position sensing in place of limit switches.
Another option may be load cells to detect the weight of the skip.

"Why not the best?"
Jimmy Carter

RE: Postion sensor for dumpster with induction loop - any experiences?

Induction loop could be a problem with rebar even if the manufacturers say it's not. I vote old school.

Have some concrete cut out in the middle with a groove trench extending off the slab and mount a weatherproof limit switch there that
is tripped by the container.

RE: Postion sensor for dumpster with induction loop - any experiences?

Big semis are backed up to loading docks all the time with few problems by simply hitting the bumper (physical stop). The fact that the dumpster is suspended is exactly what you want if using a pyramid positioner.

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