Article ex EMC News September 2001

Accurately Measure and Control Material Flow

EMC Gravimetric Systems - ideal for dosing and blending of powders / granules

EMC Gravimetric Systems are designed for the accurate measurement and control of material flowrates by weight.

These systems offer higher accuracy than simple volumetric devices as measurement is independent of material size, bulk density, temperature or fluctuations in feed hopper levels. Accuracy better than 0.5% is possible in most cases and they are ideally suited for low to medium flowrates (as low as 1 kg/hr).

Also known as "Loss-in-Weight" or "Weight Change", a typical EMC Gravimetric System includes a weigh hopper, a weigh regulator and an EMC 1493 Processor.

EMC can custom design a complete system or alternatively supply just a Processor and loadcells. Installation may simply require fitting loadcells to a hopper and wiring the 1493.

Typical Applications

EMC Gravimetric Systems and Processors have been successfully used in many industries for a variety applications such as dosing, process flow control, extruder control, blending systems and additive flow control.

A diverse range of products and materials can be measured and controlled using EMC Gravimetric Systems including:

· plastics

· tobacco

· salt

· milk products

· oxides

· pet foods

· confectionery

· powders

· grains

· granules

· pellets

· resins and glues

EMC 1493
Weight Change Processor

The EMC 1493 Weight Change Processor is an EMC designed instrument for measuring and controlling the flowrate of material in loss-in-weight systems (often known as gravimetric systems).

The unit incorporates many features and user programmable parameters and includes a keypad, 4½ digit backlit LCD display and status indicators.

The 1493 measures and controls the flowrate (kilograms per hour) of material passing through a weigh hopper and is suitable for systems where the flow regulator removes material from a weigh hopper (weight loss) and systems where the flow regulator adds material to the weigh hopper (weight gain).

It measures the weight change in the weigh hopper, calculates the material flowrate, and controls it by varying the flow regulator.

EMC 1493 Features

· Accurate flowrate measurement & control

· Automatic setup simplifies calibration

· Material totaliser

· Remote setpoint option

· Programmable limit relays

· Motor speed control output signal

· Flowrate retransmission output

· Printer output with time and date

· User programmable

· Density correction factor

· Automatic flowrate hold

Flow Regulators

Gravimetric systems require a flow regulator that adjusts the material flowrate and the most commonly used is a screw feeder driven by a variable speed motor.

However, the choice of regulator depends upon the characteristics of the material being fed and the flowrates being used.

EMC can assist with the selection of the correct type of flow regulator for your application. Typical flow regulators are:

· Screw Feeder

· Belt Feeder

· Rotary Valve

· Vibrator Feeder

· Drum Feeder

· Table Feeder

· Pump

· Restrictor Valve

EMC Manufactured Weigh Hopper and Control Panels for Loss-in-Weight
Cheese Salting System installed in USA earlier this year.

Click here for more information on Gravimetric Systems