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A range of Hycontrol level-measurement technologies is in operation at dog-food manufacturer Gilbertson and Page’s plant in Welwyn Garden City, Hertfordshire.

The systems have been individually tailored to measure products – ranging from liquids to solids and powders to pellets – across a spectrum of different level applications.

Hycontrol level systems, including bespoke display and alarm panels, are installed on 35 different silos, tanks and bins, located at all stages of the manufacturing process, from external bulk raw product silos to mixing tanks and finished product bins.

In addition, blocked-chute detection systems are fitted to a number of chutes that feed blenders, shakers and mixers around the plant for the early warning of product blockages.

The level technologies – including radar, ultrasonic, TDR, paddle and capacitance – that are employed at the plant have been selected by Hycontrol engineers to provide optimum accuracy and reliability, taking into account vessel design features, product characteristics and plant process-control requirements.

The level information from Hycontrol’s measurement systems is used for a variety of control and monitoring purposes via PLCs.

The raw-material tank farm housed outside needed Hycontrol’s Reflex Scanflex multi-point ultrasonic system to provide the continuous level measurement for the 10 silos, which store raw materials such as wheat, maize, fines and hypro soya flakes.

RP30 rotary paddle switches provide additional ‘belt-and-braces’ high-level alarms for each silo to prevent overfilling in the event of any failure of the primary measuring device.

The Scanflex features a single central control unit, which sequentially scans the signals from the 10 ultrasonic transducers on top of the silos to provide individual analogue outputs for input to the PLC via the unit’s satellite-transmission card.

This makes the system cost effective for multi-point applications, reducing wiring costs.

The enhanced echo extraction feature is claimed to ensure robust and reliable measurement signals under all operational conditions.

The two Fats and two Digester tanks are fitted with Hycontrol’s VF7 time domain reflectometry (TDR) guided-wave radar systems, connected through to local display alarm panels.

The digest acid mixer tank is also fitted with a VF7 TDR unit, which incorporates a compact integral human-machine interface (HMI) for local display.

The VF7 is effective for difficult level-measuring applications, especially where changes in process parameters – such as temperature, pressure and viscosity – can cause problems.

The VF7’s stainless-steel waveguide is also unaffected by product build-up, ensuring long-term maintenance-free reliability and accuracy in sticky applications.

The technology works by sending low-power electromagnetic pulses of 1ns width along the instrument’s probe.

Upon reaching the surface of the vessel contents, the pulses are reflected back with a signal strength that is dependent on the dielectric constant of the medium being measured.

The instrument measures the time between the emission and the reception of the signal, converting this into a 4-20mA output current.

Any weak or spurious signals are analysed and ignored by the electronics.

The narrow vessel entry requirements for the wave guide make the VF7 suitable for retrofitting to existing flanges, removing the need for expensive and disruptive tank modifications.

The units are calibrated off site prior to installation, further reducing plant disruption during commissioning and speeding up the installation process.

The finished product is pneumatically conveyed into 20 internal storage bins, which are each fitted with Hycontrol’s Microflex LR low-frequency ultrasonic level transmitters.

These loop-powered 20kHz units are suitable for measuring low-dielectric product in dusty environments where the high-power transducers’ ultra-low-frequency signals ‘cut’ though the dust and track the changing product levels.

The bins are arranged in two banks of 10 and analogue level signals from these are transmitted to two separate PLC panels.

RP30 paddle switches provide additional high-level alarms, while ME11-series low-level capacitance probes warn of impending empty bins.

The ME11 probes are also used for blocked-chute detection around the plant.

In this role, the units detect if a chute or conveyor line bridges or blocks and provide a warning to prevent further plant complications.

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