Capacitive Proximity Switches SIMATIC PXC
Monitoring Fill Levels and More
Capacitive proximity switches also operate contactless and equally respond almost instinctively when conductive or non-conductive materials in solid, powdery or liquid states have to be measured. They are particularly convincing in monitoring fill levels through non-metallic materials such as plastic or glass, and in counting objects made of various substances.
Highlights
Detection of all materials (e.g. plastic, wood, paper)
Measurement of liquid through plastic tubes or glass pipes
Measurement of aggressive chemicals
Adjustment of the operating distance on the object
Function
The sensing face of a capacitive sensor is formed by two concentrically arranged metal electrodes that are equivalent to the electrodes of an unwound capacitor. The electrode surfaces A and B are connected into the feedback branch of a high-frequency oscillator that is tuned such that it does not oscillate when the surface is free. When an object approaches the active face of the sensor, it enters the electric field in front of the electrode surfaces and causes a change in the coupling capacitance. The oscillator starts to oscillate; the amplitude is recorded by an evaluation circuit and converted into a switching command.
Switching frequency
The build-up characteristics specific to other pulse/interval conditions may result in higher switching frequencies than those specified.
Operating distance
The stated values are applicable to a target of metal which is grounded and whose area corresponds to the sensing face of the proximity switch. The real operating distance sr for nonconductive targets is dependent on the relative dielectric constanter and the characteristic value (see characteristic curve).
Built-in protection
Spurious signal suppression
Short-circuit and overload protection
Polarity reversal protection for connections
Inductive interference protection
Dielectric constants of various materials
Glass 5
Paper 2.3
Vacuum, air 1
Water 80
2008-04-29 | 