Rockwell Automation T80004 Application Note Field Loop Configuration - Manual (Page 26)

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AN-T80004 Field Loop Configuration
Issue 10 Jun 13 AN-T80004 26
Frequency/Pulse Inputs
The T8442 Speed Monitor Module is designed to monitor the speed of a rotating machine (turbine etc.)
and provide over-speed and over-acceleration trip outputs to a very high integrity. Its normal purpose is
described in its Product Description PD-T8442. This document covers possible alternative uses.
It is therefore ideal for measuring frequency inputs up to 30,000Hz with an accuracy of 1Hz or 0.01%,
whichever is greater. However, it does not provide a count of pulses, so it is of no use as an accurate
flow total integrator. A pulse count can be interpolated by multiplying the current speed by the latest
scan time (measured using a timer variable), but this is only moderately accurate.
The module must be used with its dedicated FTAs T8846 (all inputs) and T8891 (one set of outputs)
and I/O cable TC-801 which connects the module to all FTAs. The cable is shown below. This cable
allows Companion Slot operation; there is no SmartSlot cable.
The T8846 FTA allows connection of:
•
Active totem pole outputs, device powered from FTA or externally
• Active open collector outputs, device powered from FTA or externally
• Passive inductive sensors
Connection for each device is described in PD-T8846.
If the T8442 is used for pulse/frequency measurement without need for over-speed and over-
acceleration trip outputs, the T8891 FTAs are not required. These must be declared as absent in the
system configuration in the Speed Monitor template assigned to the module. For each group, uncheck
‘SOFTA Present’; this turns off the module’s diagnostics of the FTAs. Note that firmware build 133 or
later (TUV release 3.5.1) is required to turn off the diagnostics. This firmware is fitted in modules with a
manufacturing build label showing a number 2 (e.g. F2).