Sensor passive detection

Question

We have a need to limit travel on a rope being retrieved onto a drum through a pulley. We need to mount a passive non powered sensor or tag of some type onto the rope and be able to detect it within a range of 1 mtr.

We have enquired about RFID but these are typically a computer controlled solution, all we want is a "yes the tag is in range" signal to a PLC to stop the motor on the winch.

Any ideas are welcomed.

Cheers

Warren

06 3564912 (New Zealand)

warren@bandm.co.nz

albertosombri · Accepted Answer

You can use both system, RFID and optical. In the market there are many industrial RFID reader with different technologies, they can be connected to PLC or others embedded system. There are UHF readers able to detect the Tag in a range of 4-6 meters, and you can set the output power of the reader in real time. So, controlling the power, you can adjust the reading range of the reader. Alberto S.

Catwell · Answer

Warren, You could also look into rotary pulse generators. Attached to the pulley or somewhere on the rope, the device will rotate, generating pulses. Then you can could the pulses and see how far the rope has travelled. This device acts almost like an optical encoder. RFID has an increasing accuracy problem directly proportional to the distance it's being sensed. But I like the idea of wireless, bounce back, detection. What is the maximum distance you have to sense? Cabe

Chris_Pinter · Answer

Hello Warren,

This is Chris Pinter. I am an RF engineer with Pinter Electronics Consultants.

I think radios are a great way to solve problems when wires can affect results. Wireless solutions typically cost more than wired ones and the quality of the communication link is dependent on many factors that a wired solution does not have to consider.

For your problem, I think maybe a different type of solution is better. I would attach a magnet to the rope as a sensor. The magnet will be more robust then a plastic box with an RFID or radio transmitter. The magnet is also a passive device. You can then use a simple solenoid mounted on the pulley. When the magnet passes the solenoid it turns to motor off causing the rope to stop.

Now, because I love radios so much I should mention that you can use a wireless system to transmit the signal from the pulley to the motor but a wire will be able to send the signal to the motor just as well.

Hope this helps.

Chris Pinter

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Pinter Electronics Consultants

http://www.pinterec.ca