Machine Design
  • Resources
  • Members
  • Directory
  • Webinars
  • WISE
  • CAD Models
  • Advertise
    • Search
  • 3D Printing & CAD
  • AUTOMATION & IIOT
  • Robotics
  • Motion Systems
  • Materials
  • Video
  • Data Sheets
  • Topics
    Industry Markets3D Printing & CADAutomation & IIoTFastening & JoiningMaterialsMechanical & Motion Systems Medical DesignRobotics
    Resources
    Machine Design ResourcesWISE (Workers in Science & Engineering)Company DirectorySearch Data SheetsContributeDigital Edition ArchivesCSIA Exchange
    Members
    ContentBenefitsSubscribe
    Advertise
    https://www.facebook.com/MachineDesignMagazine/
    https://www.linkedin.com/company/10998894
    https://twitter.com/MachineDesign
    https://www.youtube.com/channel/UCXKEiQ9dob20rIqTA7ONfJg
    1. Archive

    Sensor Sense: Capacitive sensors

    Aug. 10, 2006
    Most proximity sensors use an electromagnetic field to sense the presence of a target metal. But there are times when it's necessary to sense nonmetallic materials such as plastics, liquids, or powders.
    Robert Repas

     

    Capacitive proximity sensor block diagram

    Capacitive proximity sensors use two metal electrodes or plates to generate a high-frequency electrostatic field. A nonmetallic target entering the field increases the dielectric constant between the plates, raising the amplitude of the oscillations. The higher amplitude triggers a level detection circuit to turn the output of the sensor on. It turns off again when the target leaves and oscillation amplitudes return to normal levels.


    Those target materials have little effect on electromagnetic fields, so inductive proximity sensors are useless in these situations. The sensing field must change from the electromagnetic domain to the electrostatic domain; the inductive proximity sensor must become capacitive.

    Capacitive proximity sensors detect a wide variety of materials. For instance, capacitive sensors are often used to detect granular or powdered materials like plastic pellets in injection-molding hoppers. And intrinsically safe units sense the level of organic materials like rice, barley malt, corn, and soybeans in possibly explosive areas, such as grain elevators.

    Two metallic electrodes or plates create the sensing element in a capacitive proximity detector. The electrodes form a capacitor in the feedback loop of a high-frequency oscillator. The amount of capacitance is a function of the surface area of the two electrodes, the distance between the electrodes, and the dielectric constant of the material between the electrodes. The capacitance is low with no target present, so the oscillation amplitude is small. A target approaching the face of the sensor changes the dielectric constant between the plates and raises the capacitance. The higher capacitance boosts the amplitude of the oscillations being measured by a level-detection circuit. When the amplitude of the oscillations exceeds a specific value, the level detector turns on the output of the sensor. As oscillation amplitude falls below the threshold, the level detector turns the sensor output off.

    Conductive targets affect capacitive sensors as well, but in a different way. When a conductive target enters the sensor field it forms a counter electrode to the active face of the sensor. The target effectively reduces the distance between electrodes and boosts the average surface area. The net result is a jump in the capacitance value, the same as for a nonconductive target.

    cannot sense through metal. Applications that measure liquid level in a metal container require either a special sight glass or nonmetallic tank well fittings to hold the capacitive sensor.

    Turck Inc. (turck.com) provided information for this column.

    Continue Reading

    Deliver Robust Automated Systems Through Servo Maintenance

    Designing a Transformable Solution for Safe Traffic Cam Installation

    Sponsored Recommendations

    Smart Factory Solutions that Connect and Protect from Amphenol RF

    Nov. 28, 2023

    Stay Connected and In Control of Your Future Factories with Littelfuse

    Nov. 28, 2023

    Turn to NKK Switches for the Widest Range of Industrial-Savvy Electromechanical Switches

    Nov. 28, 2023

    Unlocking Operational Flexibility in Manufacturing with Industria IoT

    Nov. 28, 2023

    Voice your opinion!

    To join the conversation, and become an exclusive member of Machine Design, create an account today!

    I already have an account

    New

    Using Natural Language Understanding to Power Productivity

    Intelligent Assistant Platforms Improve Conversations with Industrial Robots

    Natural Language Conversation Assistants Cross Over from Vehicles to Industrial Machinery

    Most Read

    Universal Robots Unveils UR30: Relief for Heavy Lifting

    The Cyber-physical Training Module

    Edge Computing & Gaining Value

    Sponsored

    Industrial Automation in the Age of Electrification

    Reliable and Accurate Sensing for Demanding Applications

    Industrial Internet Of Things

    Machine Design
    https://www.facebook.com/MachineDesignMagazine/
    https://www.linkedin.com/company/10998894
    https://twitter.com/MachineDesign
    https://www.youtube.com/channel/UCXKEiQ9dob20rIqTA7ONfJg
    • About Us
    • Contact Us
    • Advertise
    • Do Not Sell or Share
    • Privacy & Cookie Policy
    • Terms of Service
    © 2023 Endeavor Business Media, LLC. All rights reserved.
    Endeavor Business Media Logo