Proservo NMS81
Hauser
5
Function and system design
Measuring principle
NMS8x is an intelligent tank gauge for measuring liquid levels with high precision. The system is
based on the principle of gauging displacement.
A small displacer is accurately positioned in a liquid medium using a stepping motor. The displacer is
then suspended on a measuring wire which is wound onto a finely grooved wire drum. NMS8x
counts the rotations of the wire drum and to calculate the traveling distance of the wire and obtain
the liquid level change.
The drum is driven via coupling magnets that are completely separated by the drum housing. Outer
magnets are connected to the wire drum, with inner magnets connected to the drive motor. As the
inner magnets turn, their magnetic attraction causes the outer magnets to turn, as well, causing the
entire drum assembly to turn. The weight of the displacer on the wire creates torque on the outer
magnets generating change of magnetic flux. These changes generated in the drum assembly are
detected by a unique electromagnetic transducer on the inner magnets. The transducer transmits the
weigh signal to a CPU using a non contact principle (patented). The drive motor is actuated to keep
the weigh signal constant at set value defined by the operating command.
When the displacer is lowered and touches a liquid, the weight of the displacer is reduced by liquid
buoyancy force, which is measured by a temperature-compensated magnetic transducer. As a result,
the torque in the magnetic coupling changes, and this is measured by six hall sensors. A signal
indicating the weight of the displacer is sent to the motor control circuit. As the liquid levels rise and
fall, the displacer position is adjusted by the drive motor. The rotation of the wire drum is
continuously evaluated to determine the level value using a magnetic rotary encoder. In addition to
gauging the level, NMS8x can measure the interfaces between up to three liquid phases, and the
tank bottom, as well as spot and profile densities.
CPU
1
2
3
4
4
5
6
7
8
A
B
C
A0026724
1
Operating principle
A
Displacer position data
B
Weight data
1
Encoder
2
Motor
3
Rotary transformer
4
Shafts
5
Gears
6
Wire drum
7
Measuring wire
8
Displacer
