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156 Rockwell Automation Publication 1444-UM001D-EN-P - June 2018
Chapter 4 Measurement Definition
Normal Thrust
Also referred to as “rotor position” or “axial position”, the thrust measurement
is used to monitor thrust bearing wear and to help protect against, or provide
warning of, axial rubs.
To output this value to the controller, via the input assembly, select the
“Proportional DC” value on the Input Data page for the configured channel.
See
Select Input Data for Input Tag on page 106 .
Figure 62 - Input Data Page
Only use single-thrust motion detection (one channel) when the machine does
not have to be shut down and there is another means of verifying thrust bearing
failure. Use dual (redundant) thrust position measurements for applications
where exceeding the thrust position limits forces a machine shutdown. In this
case, the voted alarm logic is defined such that both measurements must be in
Danger before a shutdown (relay actuation) is executed.
On steam turbines, thrust position measurements are taken within
approximately 30 cm (12 in.) of the thrust bearing. The measurements monitor
the thrust collars movement between the active and inactive thrust shoes and
their subsequent wear.
The rotors thermal expansion and an increase in the required dynamic
measurement range affect measurements that are taken outside of the thrust
bearing area (greater than 30 cm [12 in.]).