Appendix; Structure Of The Measuring System; System Components; Description Of Use As A Protective System - Endress+Hauser Proserve NMS80 Functional Safety Manual

Appendix

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7 Appendix
7.1

Structure of the measuring system

7.1.1

System components

The measuring system' s devices are displayed in the following diagram (example):
7
1 Proservo NMS80/81/83
2 4 to 20 mA line
3 Switch output
4 Fieldbus (e.g. Modbus, V1)
5 Tankvision Tank Scanner NXA820
6 Ethernet
7 Computer with Fieldcare
8 Logic Unit, e.g. PLC, limit signal transmitter
9 Actuator
An analog signal (4 to 20 mA) in proportion to the level is generated in the transmitter.
This is sent to a downstream logic unit (e.g. PLC, limit signal transmitter, etc.) where it is
monitored to determine whether it is below or above a predefined limit value.
The relay contact is opened if a set level is exceeded or undershot, and if errors are
detected. For fault monitoring, the logic unit must recognize an open contact. The current
output follows the level. If errors are detected, a failure current is output.
For fault monitoring, the logic unit must recognize both HI-alarms (≥21.0 mA) and LO-
alarms (≤3.6 mA).
7.1.2

Description of use as a protective system

The Proservo is a high-precision, intelligent tank gauging device. It operates based on the
principle of displacement. A small displacer is accurately positioned in the liquid using a
multiphase motor. The displacer is suspended from a measuring wire which is wound onto
a drum. The device counts the drum rotations in order to determine the measuring
distance.
Typical measuring arrangement
5
NXA820
6
4
3
2
1
Proserve NMS80
9
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