korgy

Hey all! I am finding this forum very useful!

This may seem a bit elementary, but I am new to circuits. I am currently on a project to build a circuit for a conveyor belt that stops when it senses metal near the magnetic sensor.

I am using a 1000rpm motor that has about 1/2 HP. I want the motor to run when there is not metal, and stop when it detects metal.

Power source: 120VAC, 60hz power.

The main components are motor (have), power source (have), relay (not sure what to choose), magnetic sensor (?).

Any help is appreciated!

crutschow

To select a particular sensor you need to state the size of the (magnetic) metal to be detected and the maximum distance from the metal to the sensor.

korgy

This is the sensor I am gonna use perhaps.

http://search.digikey.com/scripts/Dk...me=391-1000-ND

crutschow

This is a magnetic sensor which should work, provided it's sensitive enough.

To sense a magnetic material you need to place a permanent magnet close to the sensor so that its magnetic field is changed by the magnetic material as it passes, which is detected by the sensor. You will likely have to experiment some with the magnet strength and placement of the magnet and sensor to reliabily detect the material.

korgy

Thanks for the reply.

As for the schematic.. the relay should hook directly into the motor.. then from the relay the sensor then the power source? I am a bit confused.

crutschow

The sensor will not power the relay. The sensor is simply a bridge circuit that changes resistance with magnetic field. This causes a voltage change at the bridge output. You will need an op amp or instrumentation (differential) amplifier to amplify this voltage change.

Then you will need a relay driver at the op amp output to drive the relay coil.

The relay contacts will be in series with the motor power line to control the motor.

You will, of course, also need a DC power supply for the sensor and op amp.