Sensor selection

[Plc_User]

In need a sensor that looks upside down at a metal part.
The metal part is at a distance from 100mm to 250mm from the sensor. The whole construction is located outside, so it has to be resistant to water that can rest on the surface of the
sensor that looks upside (it may not detect water or possible dirt on the sensor).
Inductive sensors probably don"t have those large ranges and photocells may probably detect water as an object.
Has someone experience with detection in these conditions?
What sensor should you advise?

 

[Lancie1]

It depends on the type of metal and the mass or volume of the metal part. The larger in surface area and the heavier it is, the more types of detectors will be able to sense it. For example, if it is steel or iron, and weighs 2 lbs or more, a large induction coil of wire would do the job (same type used on metal detectors used for sub-surface treasure hunting). In fact, if the metal part is large enough, you could buy an off-the-shelf metal dector and mount the sensor head under the part. Some of the better treasure detectors can be tuned to focus on certain types of metal, to some extent, with iron and steel still being the most easily detected, with gold and silver also being detected.

 

[Plc_User]

It depends on the type of metal and the mass or volume of the metal part. The larger in surface area and the heavier it is, the more types of detectors will be able to sense it. For example, if it is steel or iron, and weighs 2 lbs or more, a large induction coil of wire would do the job (same type used on metal detectors used for sub-surface treasure hunting). In fact, if the metal part is large enough, you could buy an off-the-shelf metal dector and mount the sensor head under the part. Some of the better treasure detectors can be tuned to focus on certain types of metal, to some extent, with iron and steel still being the most easily detected, with gold and silver also being detected.

Do you have specific references of types and brands.

 

[iant]

often you can think outside of the box.
'Large Induction Coil' yu could use a road type detector - the induction loop that detects cars.
when you are looking for brands of sensors there is always the usual, Omron, Sick, Turk etc.
but for special pplications have a look at Keyence.
Sorry not sure of the brand name of the in floor sensors

 

[PeterW]

Have a look at barrel ultrasonic sensors.

 

[OkiePC]

Use a thru beam or polarized retro reflective eye if at all possible to mount a polarized reflector behind the target.

Investigate using an air jacket to keep the lens clear.

http://www.keyence.com/products/sensors/photoelectric/px/px_applications_1_1.php

http://www.ifm.com/ifmus/web/pmain010_050_010_110.htm

http://www.bannerengineering.com/en-US/products/8/Sensors/765/High-Pressure,-Washdown-Rated

 

[Lancie1]

Do you have specific references of types and brands?

If I knew what metal you are trying to detect, and its size and weight, and how much room that you have to mount the sensor, then I could give you a brand. Without that, here is a bunch of waterproof treasure-hunter metal detectors. Take your pick.

http://www.google.com/#hl=en&tbo=d&sclient=psy-ab&q=water+treasure+hunter+metal+detectors&oq=water+treasure+hunter+metal+detectors&gs_l=hp.12...58813.73109.2.74797.21.16.3.0.0.8.1141.8846.2-1j3j4j5j2j1.16.0.les%3B..0.0...1c.1.2.hp.YYzVkmW8U4A&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.&bvm=bv.42080656,d.eWU&fp=b25f9c6635e21e60&biw=1024&bih=615

The waterproof coil on the end of a treasure hunter can be removed and placed under your part. The electronic control panel can be mounted remotely. The discriminator circuit has to be tuned to produce a maximum response only to the specific part and type of metal at a set distance 1 inch to 3 or 4 feet) from the coil. If you want to feed the signal into an analog PLC input, remove the headphone and connect the wire to an analog voltgage input.

There are also metal detectors made for industrial use, most commonly used on conveyors to detect stray metal pieces that have got into the product.

If you have a small part and have room to mount a reflector above the part, look at Okie's Keyence PX-H71TZ heavy-duty industrial photoelectric sensor for wet environments. You can even get one for a free trial.

 

[Ned_Flanders]

Use a thru beam or polarized retro reflective eye if at all possible to mount a polarized reflector behind the target.

Investigate using an air jacket to keep the lens clear.

http://www.keyence.com/products/sensors/photoelectric/px/px_applications_1_1.php

http://www.ifm.com/ifmus/web/pmain010_050_010_110.htm

http://www.bannerengineering.com/en-US/products/8/Sensors/765/High-Pressure%2C-Washdown-Rated

If you can have a transmitter/reciever combination I have used "Telco" photo sensors which will see through water/steam etc.

 

[OkiePC]

...a large induction coil of wire would do the job (same type used on metal detectors used for sub-surface treasure hunting). In fact, if the metal part is large enough, you could buy an off-the-shelf metal detector and mount the sensor head under the part.

That's novel. A cheap, gigantic long range prox. switch...I gotta try that one some day.