Appendix; Structure Of The Measuring System - Endress+Hauser Proservo NMS80 Functional Safety Manual

Proservo NMS80/81/83
Structure of the measuring
system
Endress+Hauser

Appendix

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 (4-20 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 specified 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, an error current is output.
For fault monitoring, the logic unit must recognize both HI-alarms (≥21.0 mA) and LO-alarms
(≤3.6 mA).
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
9
8
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