Straight talking wins orders for Coriolis meters

Since Krohne's introduction of the world's first single straight-tube Coriolis mass flowmeter in 1994, the company has found the food industry to be one of the most enthusiastic users of the technology. The reasons are, literally, straightforward. Traditional Coriolis meters with their bent and looped tubes, or split-flow tubes, proved unreliable on the typically viscous, Non-Newtonian, shear-sensitive, or solids-bearing fluids encountered in much food processing. The major advantage of Krohne's single, straight tube G-meter compared with these other designs is the low pressure drop across the meter - together with the lower operating velocities of the meter.

Another important feature of the meter that has direct appeal to food processors is its mechanical construction. The measuring tube itself is made of seamless titanium without any welds or joints. Standard surface finish is 0.8 micro m but it can be polished to 0.4 micro m if required. End connectors are also specially designed so that the process pipe inner diameter can be adapted to the inner diameter of the flowmeter to ensure a smooth transition between the two. When these adaptors are correctly tightened, they provide a smooth, crevice-free transition.

The G-meter has EHEDG (European Hygienic Equipment Design Group) approval for cleanability and sterilisability, and is manufactured with FDA approved materials for food industry use.

The meter has a multitude of measuring options, including mass flow, density, volume flow, temperature, concentration, Brix and Baume - all built into the meter's electronics and signal converters. All the converters are delivered with the Hart communications protocol on the first (of up to three) analogue output. RS485 and Modbus are also available, with Profibus and Fieldbus Foundation soon to follow.

* A typical application for the G-meter is `Skippy' peanut butter production for a South African food processor. Here, the meter is being used not just as a flowmeter, but as a ratio controller. As shown in the diagram, the mass flow of the crushed peanuts is accurately measured to enable the correct ratio of dry additives to be added to the basic material. These additives are preservatives, stabilisers, but mainly sugar, which is the key ingredient in preventing the peanut oil separating out from the butter emulsion. All the additives are expensive and a good ratio control saves money and ensures a high quality product. The screw conveyors delivering the additives into the product stream are fitted with variable speed drives, which are ratioed to the mass flowmeter readings. This posed a difficult control algorithm problem but Krohne successfully solved it and now view the plant as a very good reference site for metering very high viscosity products. The G-series meters have now routinely handled materials with viscosities as high as 250 000cP - and not just in the food industry.