Level Technologies
Floats
Designed for use on liquids, the float is the most basic form of level switch available. There are many different versions that can be mounted in either the top or the side of a tank or vessel. The top mounted variety usually consists of a guide tube with reed switches placed at the desired switch levels and has one or more floats sliding up and down the tube. The floats carry magnets that operate the reed switches. Side mounted are usually simpler, relying on a pivot action as the float rises to activate the output.
Features
low cost, wide range of options for materials and mountings. Many OEM designs.
Applications
Liquids only
Paddle Switches
Designed for use on solid materials, a paddle switch is an electro-mechanical device that relies upon product stopping its rotation. During normal operation and with no material present a synchronous motor rotates the paddle at 1 rpm. When the paddle rotation is impeded by the material surrounding it, the motor will stall and cause the micro-switch to change state.
Features
Low cost, simple design, corrosion resistant, adjustable probe lengths.
Applications
Powders, plastics, granular products, grains, cement, sand, fillers, pigments, wood dust, particulate materials.
Plumb Bob 3000 Series
The Hycontrol plumb bob level sensor is an electromechanical level measuring instrument for continuous measurement of the level or contents in tanks and silos.
The Hycontrol control unit is mounted on the top of the silo and a sensor weight is mounted at the end of a rope or tape which is wound around a motor driven roller. The weight is then driven down into the silo until it makes contact with the bulk material. When it detects the product the motor changes the winding direction and the sensor weight is driven back to the upper stop position. During this downwards movement of the sensor weight the distance is electronically measured by the rotations of the internal rope/tape roller. The microcontroller then converts the measured distance into an output signal which can be converted into a volumetric signal based on the dimensions and geometry of the silo. The output signal is updated when the sensor weight touches the bulk material.
Features
Operates in dusty atmosphere, simple automatic operation, long life motors for extended life, high temperature options.
Applications
Grain, cement, plastics, salt, sand
Hydrostatic Pressure - HP Series
The Hycontrol range of Hydrostatic Level sensors are mounted in two different ways, either submersible into the tank or externally on the outside bottom of the tank. These pressure sensors are suitable for measuring the level of corrosive liquids in deep tanks through to simple water in reservoirs or bore holes. These sensors operate by detecting an increase in pressure as the depth in the tank increases. A calibration parameter is then input to compensate for the varying specific gravities of the different liquids being monitored.
Features
Corrosion resistant materials, ATEX hazardous area options, hygienic options for food applications, wide pressure range options.
Applications
Water, chemicals, oils, milk
Bypass - 4000 Series
This measuring method is very simple. A calibrated Bypass tube is connected to the side of a tank or vessel at the top and bottom so the levels in the tank are replicated in the tube and changes in the tank equal changes in the Bypass tube.
There are then two options for level display utilizing a float inside the chamber with a magnet inside which travels up and down the tube changing magnet flaps on the outside of the tube indicating the height of the liquid in the tank with a clear visual display.
The Bypass tube also offers the option to install a level sensor into it for an electronic output of level or contents. This can be done with either a Radar or TDR level instrument. This provides a clear visual display of contents and an analogue output for retransmission of the signal if required.
Features
Chemical resistant construction, temperature ranges -200 up to 300 degrees C, pressure up to 120 bar, simple to read level display.
Applications
Boilers, chemicals, oils, solvents, hot water stream.
Conductivity
This low-cost simple liquid level switch uses the conductivity of the product to complete a circuit so it can only be used on conductive media like water. A small voltage passes between the probes when water is present which the controller will detect and operate an output relay. When the water level drops and the probes are exposed the unit will switch back to its normal state. These are typically used in simple water tank applications.
Features
Stainless steel probes, very low cost adjustable time delay.
Applications
Simple water only level switch.
Capacitance
A solid-state level switch using capacitance to detect the level of liquids and solids. The probe consists of a sensing element and an integral grounding sleeve that is separated by an insulator. There is a fixed capacitance between these two elements and this will change when product comes into the vicinity or contacts the sensing probe. The switch will then detect this change and activate the output relay. This method of detection relies on the dielectric properties of the media. The higher the dielectric the easier it is to detect (water has a value of 80+ and air is around 1).
Features
Universal for liquids and solids, low maintenance technology, unaffected by temperature, pressure. Corrosion resistant and a wide range of mounting options. Relatively low cost.
Applications
Liquids, slurries, powders, pastes, granules, pellets and can also be used for interface detection in applications such as oil and water.
Admittance
Suitable for liquids and solids - this principle uses a very similar technology to capacitance to detect the level, but has an additional reference probe. The probe consists of a sensing element and an integral grounding sleeve that is separated by an insulator and an additional reference probe. The probe will change output when product comes into the vicinity or contacts the sensing probe. The advantage of this technology is that it has the ability to work with considerable build up on the probe without false switching as it can distinguish between a coating and product level. This method of detection relies on the dielectric properties of the media. The higher the dielectric, the easier the product is to detect (water has a value of 80+ and air is around 1).
Features
Wide sensing range for liquids and solids, stainless steel construction, no moving parts, high resistance to product build-up.
Applications
Liquids, slurries, powders, pastes, granules, pellets and can also be used for interface detection in applications such as oil, water and sticky products such as bitumen, glue and paints.
Vibrating Probes
Versions for both liquids and solids are available but the operating principle is the same for all. A piezo-electric crystal is used to force a blade to oscillate at its fundamental frequency (natural resonance). When the blades come into contact with the process medium the natural frequency of oscillation is damped; the electronics sense the change in frequency that causes the unit to switch. Whilst the operating principle is the same for liquid and solids switching, the probe design for each is fundamentally different.
Features
No moving parts, simple to install, unaffected by pressure, temperature dielectric properties, wide range of mounting options.
Applications
Powders, plastics, granular products, grains, cement, sand, fillers, pigments, wood dust, particulate materials, and liquids.
Microwave Level Switch
This Level switch normally consists of two parts; a sender and a receiver placed on the outside walls of a tank or vessel, on opposite sides. The sender emits a burst of microwave energy towards the receiver. This burst of energy is transmitted approximately 200 times each second. If a sufficiently reflective or absorbent material interrupts the line of sight between these two units, the energy will not reach the receiver. Any loss in signal at the receiver will trigger a change of state and operate a relay to indicate high or low condition. The sensitivity is adjustable to cater for a wide range of materials.
Features
Long ranges, non-invasive, wide temperature range.
Products
Granules, flakes, stones, sands, cement, fillers, powders.
Microwave Flow Switch
The Microwave switch provides an effective way of detecting the flow or no-flow of a wide range of particulate materials. The flow switch uses a microwave Doppler effect and is noninvasive. During operation the sensing head transmits a continuous low power, microwave beam towards the flowing product. Some of these microwaves are reflected back to the sensing head and are then analysed as to whether the product particles are moving or stationary objects.
The highly penetrating microwave beam passes through any build-up on the transmitter face and will even detect through pipes of non-conducting materials such as plastic and ceramics. The switch is best suited for the detection of materials such as dry solids, granules, flakes and powders. This technology can be combined with the blocked chute detector to provide a flow or no-flow output and blocked or clear chute indication for maximum plant protection.
Features
Non-invasive, wide temperature range.
Products
Granules, flakes, stones, sands, cement, fillers, powders.
Radar
Two types of non-contact radar are possible, Pulse and FMCW. Hycontrol's radars' use Frequency Modulated Continuous Wave. FMCW radar uses a high frequency signal (~10GHz) which increases linearly, by 1GHz during the measurement cycle. The signal emitted is reflected from the target surface and received at a time-delayed frequency. The difference between the transmit frequency and the received frequency is directly proportional to the distance measured, i.e. a large frequency difference corresponds to a large distance and vice versa. This frequency difference is transformed via a Fast Fourier Transformation (FFT) into a lower frequency spectrum and the distance is then calculated from this spectrum.
Features
High accuracy options, long range unaffected by temperature, pressure, vacuum, foam, non contact suitable for aggressive media.
Applications
Liquids and solids, pellets, granules, acids.
TDR (Time Domain Reflectometry)
Often referred to as Radar on a Rope or contact radar, TDR uses pulses of low power microwaves sent along a conductor (cable or rod) immersed in the product. Where the waves meet the product surface they are reflected back. The intensity of the reflection depends upon the dielectric constant of the product. The higher the dielectric constant the stronger the reflection will be, eg 80% reflection for water. The instrument measures the time between transmission and reception that is proportional to the distance.
Features
Suitable for solids and liquids, immune to coating, long measuring range, measures interface, unaffected by dust, temperature, pressure, steam, foam, vacuum. High accuracy.
Applications
Powders, granules, flakes, pellets, liquids, slurries, paints, hot bitumen.
Ultrasonic
Non-contact ultrasonic level measurement is one of the most versatile level measuring technologies and is suitable for both liquids and solids measurement. It can be used for continuous or point level detection. The principle of operation is often referred to as 'time of flight'. An ultrasonic pulse is emitted from a transducer down towards the media and is reflected back from the surface. The time it takes to travel from and to the transducer is directly proportional to the distance traveled.
Features
Liquids and solids, low cost, wide range of applications, simple to install and non- contact, long measuring ranges up to 60m.
Applications
Powders, pellets, granules, slurries, pastes and liquids.
Thruwall
This range of instruments can be used for continuous or point level detection of liquids. A transducer attached to the outside wall of the tank bottom transmits a pulse of high frequency sound through the tank wall and the fluid until it reaches the fluid's surface where it is reflected back. The time taken for the pulse to travel from and to the transducer is proportional to the depth of the fluid. Simple level switching can be achieved by mounting the instrument onto the side of the tank wall.
Feature
Non-intrusive, unaffected by pressure or surface foam, simple retrofit mounting.
Applications
Liquids, fuel, foods, acids, spirits, chemicals, pharmaceutical.