Radar level transmitter proves itself at Aston Martin

At the tank inlet, two large transfer pumps force the incoming stream downwards, heavily aerating the water to accelerate and improve the separation process. The coagulated solids settle at the bottom of the tank and the clean aerated water at the surface flows over a weir to be further treated and re-used in the paintshop. The solids at the bottom are periodically pumped away for drying and disposal. "This part of the paintshop process is very important, it is one of those pinch points – issues in the effluent treatment can quickly affect the paint process, then we cannot paint the cars, so production is directly affected," explained an Aston Martin engineer. 

The ‘coagulation tank’ is approximately 3.5m deep, 5m wide and 8m long, with a strong effluent flow of up to 140000l/min. Controlling the optimum level or stopping any overflow is crucial and not without difficulty, the surface is turbulent, it foams readily and heavily, build up on any form of 'contact' device quickly happens and causes problems. After initially installing a guided wave radar, and trying point level switches, they found the heavy, unpredictable high build up levels and contamination were so severe on the probes that it caused false readings and needed frequent cleaning. The poor measurement availability and high maintenance were unwelcome in such an important area. The ‘coagulation tank’ is a hazardous area, the heavily aerated water means that anyone falling in would sink ‘like a stone’, so minimising any personnel working in the area is a priority.

Almost two years ago, the units were changed for a contactless VEGAPULS WL61 radar level sensor by the Aston Martin team. Designed for water and waste water applications, it features an IP68 housing with an encapsulated antenna, which is suited to use in the harsh operating environment in an effluent plant. 

The sensor is further suited this application because the liquid density and substances contained within the liquid have no bearing on measurement accuracy. Most importantly, the device can cope with all reasonable levels of foam due to the signal sensitivity and the 80mm antenna, which focuses signal for optimal performance. "The readings we now get are to the mm which is extremely accurate and allows us to have a greater level of control, especially as this measurement also governs the ‘Water Make Up Valve’ which operates to re-level the tank as water evaporates due to the process. All of the control strategy for the water system was re-written after installation due to the greater level of accuracy and so far we have enjoyed a 100% efficiency rate to date,” said the engineer. 

The safety surrounding the ‘coagulation tank’ has also been increased as it is no longer necessary to enter the guarded area around the tank to clean off build up. Being non-contact is ideal in this application, so if the pit is cleared out, there will be no sensor damage.