Flow Measurement - A need and difiiculty

During the past number of years, we have seen the move by the dairy, food and beverage
industry, toward using poly bags and poly bags in boxes as a packaging medium. This
move has necessitated the development of machinery to accurately fill these bags.
Certain machines use a positive displacement cylinder that contains a predetermined
volume, while other machines use a predetermining counter device, which is interfaced
with a flow measurement device.

There are a number of flow measurement devices on the market today ranging from
positive displacement meters to electro-magnetic flow meters. Positive displacement
meters are very accurate meters but tend to be rather expensive and usually require a
great deal of maintenance. Today, many strides have been made in improving positive
displacement meters by incorporating pistons that can be CIP’d and the use of electronic
pulse transmitters in order to interface them with electronic counters. They still have
many applications for this type of device especially where very accurate measurement is
required with products that are non-conductive of electricity such as oils and certain types
of syrups.

Because of the expense of the positive displacement meters, many companies in the filler
industry decide to use what is known as a turbine meter. This meter works on the
principal of a turbine rotor, which spins as product is passed through it. As the blades of
the rotor spin, they pass a transducer, which senses that the blade has passed it and in turn
creates a pulse, which is then sent to a counting device. These pulses in turn are
converted into volumetric units such as litres, and gallons. Initially, these turbine devices
seemed to work pretty well but with the advent of acid sanitizers and high speed cleaning
systems many problems started to develop with the turbine meters. In addition, the acid
sanitizers start to corrode the rotor blades thus changing the number of pulses sent for a
given volume of product. Because of its nature, the turbine meter also requires that for
each different product a different factor (K-factor) be entered into the pre-determining
counter. When one combines all these problems, it is very difficult to accurately fill a
bag with a known volume of product on a consistent basis.