Basic Proximity Sensor Operations Posted on February 17, 2017 by Brandy McNeil Sensing: The inductive proximity will sense all metals. The exact point at which a target will be detected is influenced by the type of metal, its size and surface area. The following charts show the sensing fields for a standard target: 45mm sq., mild steel, 1mm thick. Standard Range Shielded – Can be mounted flush with metal surface. Extended Range Non-shielded – Can not be mounted flush with metal surface The two most common approach directions are axial (head-on) and lateral (from the side). Detection occurs at the point where the target first touches the envelope of the sensing curve. The curve shown is for a standard target and must be corrected for other size targets. Correction Factors for Typical Target Materials Based on Standard Size Target Material Corrective Factor Steel 1020 1.00 430 Stainless 1.03 302 Stainless .85 Brass .50 Aluminum .47 Copper .40 Operation of Photo-Electric Sensors Diffuse-Reflective This type of sensor detects the reflection of transmitted light from the surface of an object. Shortest sensing range of all photoelectrics. Retro-Reflective This type of sensor utilizes a special reflector to return the beam directed at it from the sensor. An object between the sensor and reflector is senses when it interrupts the beam. Medium sensing range. Thru-Beam Separate emitter and receiver provide maximum detection range and most positive type of sensing for opaque objects. When an object interrupts the beam from emitter to receiver, the object is detected. Operation of 2-wire and 3-wire sensors A/C 2 Wire NO 2-Wire Devices: 2-wire sensors are intended to be connected tin series with the controlled load. Because these sensors derive the power to energize their internal electronics through the load they control, a minimum current is drawn through the load when the sensor is in the open stat. This current is so small that it can be ignored and will not turn on electro-mechanical devices such as relays and solenoids. However, this current could be enough to operate an electronic load. Cutler-Hammer’s 2-wire sensors have the lowest leakage current in the industry and are suitable for many electronic loads. A/C 3 wire NO/NC or DC PNP 3-WIRE DEVICES: 3-wire sensors derive their power directly across the line and therefore have no current leakage to the load. Operation of Logic Modules On Delay Adjustable delay between time object is sensed and time switch function occurs. Off Delay Adjustable delay between time object leaves sensing field & time switch transfers back to non-sensing state. On & Off Combination of Above. Delayed Single Shot Adjusts length of time switch remains in “ON’ cycle after object is sensed regardless of length of time object stays in sensing field. “ON” cycle can also be delayed after object is first detected.