Coat-Resist Point Level Switches


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.  1/2 " 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