Behavior - Allen-Bradley 1444-TSCX02-02RB User Manual

Behavior

The module can process two independent tacho signals from a range of
sources.
For 'simple' TTL signals, the main module is equipped with two local tacho
inputs. Trigger threshold for these inputs is fixed at 2.5V
For more complex signals, a TSCX module can be used. This option provides
the possibility of tacho transducer power, support for a range of transducer
types, variable trigger threshold, and multiple event per revolution signals.
Conditioned tacho signals (TTL and one event per revolution) can then be
made available to multiple main modules via the tacho bus. A TSCX module is
also required to support cross module synchronization; that is the advanced
(On-demand) data, which are synchronized across multiple modules. Where a
TSCX module is being used, make sure that the main module tacho edge
detection (the preceding attribute 21), matches that configured for the TSCX
module.
To verify the validity of the Speed and the captured Maximum Speed value, the
module applies the following rules:
• After power-up or configuration download, the speed value is held at
zero rpm until three tacho pulses have been processed. This process is
used to avoid a 'ghost' pulse that can cause a spurious high-speed
measurement.
• If there is a Tacho Fault, the speed measurement continues to be
performed and the speed value is presented regardless of any effect due
to the fault. However, in regards the Maximum Speed value:
• The Maximum Speed value is not updated while a Tacho Fault is
present.
• New maximum speed evaluations are implemented on slightly
historic speed values (around1 second old). This evaluation makes
sure that if the tacho goes into fault that any speed measure that is
made during the transition is not considered for the Maximum Speed
value.
• Maximum Speed values are not considered for approximately 2
seconds, and at least four tacho events, following a Tacho Fail to OK
transition.
Although the preceding process cannot completely eliminate the possibility
that a faulty tacho probe or loose wire can trigger spurious maximum speed
values, it is designed to minimize the likelihood of this happening.
Where no tacho signals are available, the module can accept two speed values as
part of the controller output data. While unable to support tracking filters,
they can (if nominated as a 'tacho' source) drive speed-related FFT bands.
For redundant tacho mode, refer to the Module Control Object, attribute 24.
Rockwell Automation Publication 1444-UM001D-EN-P - June 2018
CIP Objects Appendix A
447