• Coat-Resist Point Level Switchs


    RF Admittance Point Level Switch

    COAT-RESIST is a compact point level switch with integral electronics, based on RF Admittance measurement technology utilizing a three electrode design with active shield compensation. It is superior in performance to conventional capacitance based systems that often suffer from false level detection due to service material adhering to the probe electrode. It offers a satisfactory solution in tough environments where service material has a tendency to coat, where there is bridging (build up) of material between the probe electrode and side wall of the vessel, where, material particles having electrostatic charge float in the vicinity of the sense electrode, and the vessel internal temperature is high. Such environments are often encountered in electrostatic precipitators wherein no other instruments are suited. The instrument has a built in discharge device to protect it from damaging effects of static electricity.

    Salient Features:

    • Not affected by material build up on side walls and coating on probe
    • Protected against frictionally induced static charge due to material movement in the vessel
    • High sensitivity so operates reliably in low dielectric materials like Fly ash and Plastic chips
    • Bar graph LED display for ease of calibration and material trend indication
    • Built-in Universal switched mode power supply for AC / DC operation
    • Field selectable Fail-safe mode for High and Low level operation
    • Field adjustable switching delay for probe covered and uncovered condition
    • Robust in construction to withstand the rigors of plant environment
    • High temperature versions available on request
    • Various mounting arrangements available to suit customer needs
    • Remotely mounted electronics version also available on request

    Bridge Construction

    Operating Principle
    The probe comprises of three elements; Sense, Shield and Ground electrically insulated from each other by means of suitable insulators. The Sense element and the vessel wall (Ground) serve as the two electrodes of an electrical capacitor with the service material as the dielectric. A change in material level causes a change in the Admittance which is measured by the electronics. A Radio frequency oscillator generates the measuring frequency. An impedance transforming shield isolation amlifier is used to drive the shield actively to maintain the equipotentiality between the probe and shield electrodes thereby immunizing the probe from build up and coating. For clarity please refer to the figure on the left.

    Applications :
    Level limit detection of fine, coarse, solids of low dielectric constant that have a tendency to stick coat and develop static charge at high vessel temperatures and in bulk material handling. Can be used for level detection of powders, sand, sugar, pulverized coal, food grains, cement, stones, gravel, flyash, bed-ash, clinker etc. Coat-Resist finds use in cement plants, power plants, ash handling systems, soap and detergent plants, paints and emulsion plants etc.


    Technical specification

    Housing

    Cast Aluminum weather proof powder coated

    Cable entry

    2 Nos.  ½” BSP / NPT

    Cable gland

    2 Nos.  Single/ Double compression size         
    1/2” BSP / NPT / Brass / Stainless steel NG20

    Tolerable ambient Temp

    0°c to 60°c 

    Power Consumption

    5VA approx.

    Mains supply

    90 to 265 V AC, 50 / 60 Hz or 18 to 55 V DC

    Fail safe mode

    High / Low   field selectable

    Outputs

    One/two sets of potential free c/o contacts
    rated at 6Amps 230V AC 50 Hz for non inductive loads or
    Open collector PNP output limited to 100ma max at 24V DC

    Indication: 

    Red    LED for alarm

    Sensitivity and material

    trend Indicator

    Ten step Bar display                      

    calibration     

    Through multi turn potentiometer

    Response Time

    0.2 Seconds typical

    Switching delay

    Adjustable up to 20 seconds (covered & uncovered)

    Switching Hysteresis

    0.2 Pf Typical