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ControlLogix 7252 LDT Interface Manual
Revision 1.5
LDT Modes and Signals
The 7252 module supports four type of LDT transducer signaling:
1. Start/Stop Mode
The Start/Stop signal interface of the 7252 module is differential RS-422 output. The module initiates a start pulse a
minimum of 1.0 microsecond in duration. Within 50 nanoseconds after the leading edge of the start pulse, the LDT will
generate an output start pulse of 2 microseconds in duration. An output stop pulse of 2 microseconds in duration will
follow from the LDT. The time it takes from the leading edge of the LDT output start pulse to the leading edge of the
LDT output stop pulse is proportional to the distance from the null zone to the LDT magnet. The order of these pulses
is illustrated in the following figure.
2. Control Pulse Mode
The Control Pulse signal interface of the 7252 module is a differential RS-422 output. The 7252 module initiates a
start pulse a minimum of 1.0 microsecond in duration. After the start pulse is received, the LDT will generate a stop
pulse of 2 microseconds in duration. The time between the leading edge of the start pulse to the leading edge of the
stop pulse is proportional to the distance from the null zone to the LDT magnet. The order of these pulses is illustrated
in the following figure.
