Consists of two conducting bodies separated by a non-conducting (dielectric) material. Two electrodes are coupled together, and integrated in a high frequency oscillator. As a target enters the electric field, increasing the capacitance, oscillation begins. When the amplitude reaches a high enough level, a change in signal state is triggered.
Contains an infrared LED and a light receiver. Light from the LED is directed into a prism which forms the tip of the sensor. With no liquid present, light from the LED is reflected within the prism to the receiver. When rising liquid immerses the prism, the light is refracted out into the liquid, leaving little or no light to reach the receiver. Sensing this change, the receiver actuates electronic switching within the unit to operate an external alarm or control circuit.
Light guidance is based on the physical effect of total reflection, whereby light coupled into a glass fiber is repeatedly reflected back into the glass fiber from the boundary surface. When rising liquid immerses the fiber, the light is refracted out into the liquid, leaving little or no light to reach the receiver. Sensing this change, the receiver actuates electronic.
A high frequency sweep signal is radiated from the sensor tip into the tank. The media will act as a virtual capacitor, which together with a coil in the sensor head, will form a circuit creating the switch point signal.
Detects absence or presence of liquids using a light transmitter and receiver.
Inside the probe tube there is a rigid wire made of magnetostrictive material. The sensor circuitry emits pulses of current through the wire, generating a circular magnetic field. The level transmitter is a magnet, which is integrated into the float. Its magnetic field magnetizes the wire axially. Since the two magnetic fields (float & wire) are superimposed, around the float magnet a torsion wave is generated which runs in both directions along the wire. One wave runs directly to the probe head while the other is reflected at the bottom of the probe tube. The time is measured between emission of the current pulse and arrival of the wave at the probe head. The position of the float or the tank level is determined on the basis of the transit times.
A micro-controlled sensor transmits current impulses through an immersed sensor (electrode) into the media and is measured when compared to an electrically insulated counter-electrode or the tank wall (ground). The loss of current into the media leads to a linear voltage drop on its electrical resistance which is proportional to the tank filling level. The difference in voltage between the tip of the rod and the tank wall is measured.
Pressure (Hydrostatic, Submersible)
Operate by measuring the weight or pressure exerted on the sensor diaphragm by the liquid above the sensor which is proportional to the tank filling level. Lighter weight fluids exert less pressure on the pressure sensor than heavy fluids, so specific gravity of the liquid must be known in order to calculate level properly. Typically 2-wire devices, transmitting a 4-20mA current output with 24VDC excitation. Can be either threaded into a port at the base of a tank, or “submersible” types can be suspended on a cable from the top of the tank. The cable is reinforced so that there is no stretching and also contains a small air tube so that the sensor can reference the liquid pressure to atmospheric pressure. Pressure in PSI = Liquid Level (in feet) x (Specific Gravity x 0.433).
Consist of an antenna inside the tank and remote mounted electronics. They work by transmitting high-frequency microwave signals that reflect off of the liquid surface and are returned to a receiver. The instrument electronics measure the time it takes from transmitted microwave signal to return of the echo.
The sensor continuously transmits pulses of high frequency sound which travel away from the sensor, hit the surface of the liquid and return to the sensor. The instrument electronics measure the time it takes from transmitted sound to return of the echo.