260 Rockwell Automation Publication 1444-UM001D-EN-P - June 2018
Chapter 10 Operate the Module
Speed Input Fault Detection
Speed input fault detection is dependent on the type of input provided. The
following table lists each of the supported types of speed input and how the
module manages fault detection for each of them.
Tachometer Signal Condition Input Fault Detection
Transducer fault detection is based on bias voltage level, measured speed or on
tachometer signal conditioner module fault as follows:
When a fault is detected, it is communicated as simply “Transducer Fault” on
the local bus. Further detail is available in the Tachometer Signal Conditioner
Module Status assembly structure on controller input (see I/O message
formats, module status structure).
Digital Inputs
Two inputs are provided to accept TTL signals. TTL signals need a clear
distinction between ‘low’ and ‘high’ values such that a trigger threshold of 2.5V
does not falsely trigger on high or low signal level or noise.
These inputs are intended for control functions, such as a switch for turning
ON/OFF startup multiplier function.
Source Fault Detection
Local TTL Tach Input No fault detection is associated with TTL signal input.
However, an associated tachometer status signal, a TTL,
can be wired to the associated digital input for the
selected speed input. When the local Logic Inputs are
used as described in the preceding statement, leave open
for a Tacho OK state and short the appropriate input to
trigger a Tacho Fail condition.
Tach Bus No fault detection is associated with the TTL signal itself.
However, the tachometer signal conditioner module
communicates transducer status via additional signal
lines on the Local Bus.
I/O Speed When speed is communicated from the controller, as tags
in the controller output assembly, the module reads speed
input status from output assembly bits 3 (Speed 0 OK) and
4 (Speed 1 OK). When used, set the Speed OK bit (= 1) for
FAULT, or 0 for NORMAL.
Fault Detection Method Description
Bias Fault Bias level fault detection functions similarly to bias fault
detection for the normal channel inputs (see the
preceding information).
Speed Fault Considers the transducer is in fault of the pulse rate
(equivalent) is slower or faster than the specified speed.
Module Fault The Tachometer Signal Conditioner expansion module
detects a module fault.
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