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ControlLogix 7252 LDT Interface Manual
Revision 1.5
Module Overview
The 7252 module is a two-channel LDT interface module that resides in a Rockwell Automation
ControlLogix rack.
This module is capable of connecting up to two independent LDT sensors with max 32-bit resolution for
position. This module also has two latching inputs, one for each channel, which can be used to capture the
sensor’s data.
The 7252 module communicates with the PLC using input and output registers. The Data value, Velocity,
Latched Value, and Status information are reported to the Input Registers. All module setup parameters,
including Preset Value, Count Direction and Velocity Response Time are programmed through Message
Instructions.
The Output registers assigned to the module can be used to Apply the Preset or to send the PLC’s Central
System Clock-Time to the 7252 module. This optional and additional feature causes the module to use this
system time and the sensors velocity data to calculate an Interpolated or “Look Ahead” Data value.
The 7252 module stores its parameters in a non-volatile flash memory when power is removed so it is not
necessary to program the module at every power up. However, this flash memory is good for a minimum of
10,000 write cycles, so the module must not be programmed during every machine cycle.
The module has two opto-coupler latching inputs that will capture the scaled sensor data on the rising,
falling, or both transitions of the input. These inputs can be wired to be sinking or sourcing and will activate
when they see a voltage level between 8 and 24Vdc across the + and – latch terminals.
Through the use of different rack Assembly Instances, the 7252 can be configured to operate with one or two
of the available channels. Disabling the unused channel is recommended for improving the throughput time.
