Principle Of Measurement; Level Measurement; Interface Between Two Products - Honeywell 854 ATG Series Instruction Manual

Introduction

1.1 Principle of measurement

Figure 1.1 Principle of measurement
The principle is based on detection of variations in the buoyancy of a displacer. The displacer is suspended from
a strong, flexible measuring wire which is stored on a precisely grooved measuring drum.
The shaft of the drum is connected to the stepper motor via a magnetic coupling.
The apparent weight of the displacer is measured by a force transducer. The actual output of the force
transducer is compared with a desired value for the apparent weight of the displacer. If a discrepancy exists
between measured and desired value, an advanced software control module adjusts the position of the stepper
motor.

1.1.1 Level measurement

A level variation of product, in which the displacer is partially immersed, causes a change in buoyancy, which will
be detected by the force transducer. The resulting difference between measured and desired value will cause a
variation in the position of the stepper motor and consequently raise or lower the position of the displacer until
the measured value equals the desired value.
To avoid oscillations, a certain hysteresis and integration time is software adjustable. This results in a stable and
accurate averaged level measurement.
The stepper motor turns one revolution for every 10 mm of vertical movement of the displacer.
One revolution is divided into 200 steps, therefore one step is equivalent to 0.05 mm. This resolution is direct
consequence of the stepper motor principle. The correct functioning of the stepper motor is continuously
checked. This is achieved by decoding the unique pattern of an encoder disk mounted on the motor shaft.

1.1.2 Interface between two products

Measurement of the interface between two products is achieved by sending an interface command to the gauge.
This causes the stepper motor processor to move the displacer to a position where the apparent weight of the
displacer matches a pre-programmed set point.
Instruction manual 854 ATG Page 7