AMCI ControlLogix 7252 LDT User manual

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ControlLogix 7252 LDT Interface Manual
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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.

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General Information
Important User Information
The products and application data described in this manual are useful in a wide variety of different applications.
Therefore, the user and others responsible for applying these products described herein are responsible for determining
the acceptability for each application. While efforts have been made to provide accurate information within this
manual, AMCI assumes no responsibility for the application or the completeness of the information contained herein.
Throughout this manual the following two notices are used to highlight important points.
WARNINGS tell you when people may be hurt or equipment may be damaged if the procedure is not followed
properly.
CAUTIONS tell you when equipment may be damaged if the procedure is not followed properly. No patent liability is
assumed by AMCI, with respect to use of information, circuits, equipment, or software described in this manual. The
information contained within this manual is subject to change without notice. UNDER NO CIRCUMSTANCES WILL
ADVANCED MICRO CONTROLS, INC. BE RESPONSIBLE OR LIABLE FOR ANY DAMAGES OR LOSSES,
INCLUDING INDIRECT OR CONSEQUENTIAL DAMAGES OR LOSSES, ARISING FROM THE USE OF ANY
INFORMATION CONTAINED WITHIN THIS MANUAL, OR THE USE OF ANY PRODUCTS OR SERVICES
REFERENCED HEREIN.
Standard Warranty
ADVANCED MICRO CONTROLS, INC. warrants that all equipment manufactured by it will be free from defects,
under normal use, in materials and workmanship for a period of [18] months. Within this warranty period, AMCI shall,
at its option, repair or replace, free of charge, any equipment covered by this warranty which is returned, shipping
charges prepaid, within one year from date of invoice, and which upon examination proves to be defective in material
or workmanship and not caused by accident, misuse, neglect, alteration, improper installation or improper testing. The
provisions of the “STANDARD WARRANTY” are the sole obligations of AMCI and excludes all other warranties
expressed or implied. In no event shall AMCI be liable for incidental or consequential damages or for delay in
performance of this warranty.
Returns Policy
All equipment being returned to AMCI for repair or replacement, regardless of warranty status, must have a Return
Merchandise Authorization number issued by AMCI. Call [phone] with the model and serial numbers along
with a description of the problem. A “RMA” number will be issued. Equipment must be shipped to AMCI with
transportation charges prepaid. Title and risk of loss or damage remains with the customer until shipment is received
by AMCI.
24 Hour Technical Support Number
Technical Support, in the form of documents, FAQs, and sample programs, is available from our website,
www.amci.com. 24 Hour technical support is also available on this product. For technical support, call (860) 585-
1254. Your call will be answered at the factory during regular business hours, Monday through Friday, 8AM - 5PM
EST. During non-business hours, an automated system will ask you to leave a detailed message and the telephone
number that you can be reached at. The system will page an engineer on call. Please have your product model number
and a description of the problem ready before you call.

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Table of Contents
Installing the 7252 Module Chapter 1 4
Hardware Overview Chapter 2 5
Module Specifications 5
Front Panel & LED Function 6
Connector Pinout 7
Latching Input Wiring 7
Wiring Notes 8
LDT Modes and Signals 9
Programmable Parameters Chapter 3 11
Transducer Fault Latch 11
Count Direction 11
Velocity Update Time 11
Measurement Unit 11
LDT Mode 12
LDT Gradient 12
Full Scale Length 12
Full Scale Counts 12
Preset Value 12
Apply Preset 12
Latched Input 13
Limit Switch Position 13
Interpolated Data Value 13
Message Instructions Chapter 4 14
Configuration Tab 14
Writing Data Setup 15
Reading Data Setup 15
Communication Tab 16
Extended Error Codes 16
Setup Data Chapter 5 17
Reading Status Data Chapter 6 18
Input & Output Data Chapter 7 19
Input Registers 19
Status Bits 20
Input Register Description 21
Output Registers 22
Command Bits 22
Apply Preset Programming Cycle 22
Interpolation Command Programming Cycle 23
Specification Revision History Chapter 8 24

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Chapter 1: INSTALLING THE 7252 MODULE
Configuring the ControlLogix System
1. Open RSLogix 5000 and the project in which you want to install the AMCI 7252 module.
2. Right click on I/O Configuration in the Project Tree.
3. Select New Module.
4. Select the following module type and description from the list that appears.
Type = 1756-MODULE
Description = Generic 1756 Module
5. Click on OK.
6. Enter the following module properties.
Name: Your Choice (must begin with a letter)
Description: Your Choice
Comm Format: Data-DINT (must be Data-DINT)
Slot: location of 7252 module
7. Enter the Connection Parameters from the following table. Please note that the 7252 module can be configured in
two ways, depending on how many channels are being used. Disabling the unused channel is recommended
because the module will stop all activities associated with the unused channel, which will improve the throughput
time.
Owner Controller Listen Only
Parameter Assembly
Instance Size in 32 bit words Assembly Instance Size in 32 bit words
1 Channel
INPUT
101 5 101 5
OUTPUT
111 2 115 1
CONFIGURATION
1 0 5 0
2 Channels
INPUT
102 10 102 10
OUTPUT
112 4 115 1
CONFIGURATION
2 0 5 0
The Owner Controller setup will be used in most instances. The Listen Only setup should only be used by the
listening processor(s) in systems with more than one PLC. Please note that the RPI time of the Listen Only
processor must be greater than or equal to the RPI of the Owner Controller, and the number of channels on the
Listen Only processor must match the number of channels on the Owner Controller.
8. Click on Next >
9. Set the RPI (Rate Packet Interval) Time to the desired value. For the 7252 module, the RPI parameter has a range
of 0.5 to 28ms, with a recommended RPI time of 5ms.
10. Click on Finish >>
The module should now appear in the project tree. The Input data will be referenced as Local:X.I.Data[Y] and the
output data will be referenced as Local:X.O.Data[Y] where “X” is the slot number and “Y” is the word number.

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Chapter 2: HARDWARE OVERVIEW
Module Specifications
Current Draw: 400ma @ 5Vdc from PLC backplane
Throughput Time: 0.2ms to 1.2ms depending on channels used.
RPI Value:0.5 to 28ms, with a recommended RPI time of 5ms.
External Power: The 7252 module requires the use of an external +24Vdc power supply that is used power the input
isolation circuitry and can also be used to power sensors that operate on 24Vdc
Voltage Range = +24V dc (± 20%)
Current Draw = 150mA. Add this amount to your LDT encoder’s current draw when sizing your
external 24Vdc power supply.
5Vdc supply The 7252 module also uses the external power supply to generate a 5Vdc user power supply
that can be used to power encoders and or sensors that run on 5Vdc. This 5Vdc supply can
supply a maximum of 500mA (± 5%) of current.
Latching Inputs The Latching Input terminals accept an up to 24VDC signal across pins 17-15, 18-16, The
latching function is performed as programmed when power is applied/removed, OFF to ON
and/or ON to OFF, to/from the input.
Voltage Range: 0 to 30Vdc
On State: 8 to 30Vdc
Off State: 0 to 2Vdc
Current Draw: 10mA @ 24Vdc
The latching inputs must be on for between 0.2ms and 1.2ms, depending on the number of
channels being used.
Environmental Conditions Operating Temperature: 0 to 60° C
Relative Humidity: 5 to 95% (non-condensing)
Storage Temperature: -40 to 85° C
EDS File An EDS file for the 7252 module can be downloaded from the Tech Library section of AMCI’s website,
www.amci.com.
FLASH Memory
The 7252 module’s parameter values are stored in a non-volatile Flash memory. This memory type can store parameter
values in the absence of power for over twenty years, but you can only write to it a limited number of times before it
will be damaged. The Flash Memory used in the 7252 module is guaranteed for a minimum of 10,000 write cycles.

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Front Panel:
The following is a list of possible causes of Transducer Faults
By default, transducer fault errors will be removed as soon as the problem has been corrected. However, if the 7252
module has been programmed for Transducer Fault Latch, the status LED will remain blinking green until the Clear
Latched Transducer Fault command has been sent from the Output Registers. Cycling power to the module will also
clear a Latched Transducer Fault.
AMCI LDT
Status
OK
Status LED
Solid Red Data Flash Memory Fault
Blinking Red/Green Module Hardware Comm. Failure
Blinking Red Non Clearable Transducer Fault
Blinking Green Clearable Transducer Fault
Solid Green No Errors
OK LED
Solid Green: Module Owned, two-way communication
Blinking Green: PLC in Program Mode or rack configuration not correct
Blinking Red: Communication between module and PLC interrupted, as
when a new program is downloaded to the PLC.
•
Broken Transducer cable
•Improperly wired cable
•Non-compatible transducer
•Magnet is not on the sensor
•Magnet is on the sensor but outside of the usable range
•External Power supply not attached to both the 7252 module
and the sensor

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Connector Pin Out:
The input connector consists of a Removable Terminal Block with the Rockwell Automation Part Numbers 1756-
TBCH (36 position cage clamp) or 1756-TBS6H (36 position spring clamp). The terminal block is not supplied with
the 7252 module.
Latching Inputs Wiring
The following two diagrams show how you would wire the 7252 module’s opto-coupler latching inputs to either
sourcing or sinking devices.
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
External +24V
GND 2
Channel 2 Interrogate –
Channel 2 Interrogate +
Channel 2 Return -
Channel 2 Return +
Earth Ground 2 (shields)
Latch Input channel 2 -
Latch Input channel 2 +
External +24V
GND 4
+5Vdc out 2
Earth Ground 1 (shields)
GND 1
Channel 1 Interrogate -
Channel 1 Interrogate +
Channel 1 Return -
Channel 1 Return +
Earth Ground 3 (shields)
Latch Input channel 1 –
Latch Input channel 1 +
Earth Ground 4 (shields)
GND3
+5Vdc out 1
+ Latch Input
- Latch Input
Sourcing Devices
Power Supply
+ 8 to 30Vdc
Common
+ Latch Input
- Latch Input
Sinking Devices
Power Supply
+ 8 to 30Vdc
Common

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Wiring Notes
•Use the information provided by the transducer’s manufacture to determine the type and maximum length of
cable that should be used to connect the sensor to the 7252 module.
•When plugged into the 7252 module, pin 1 is located in the upper right hand corner.
•External +24Vdc (pins 2 and 20) are internally connected together.
•GND1/2/3/4 (pins 3, 4, 21 and 22) are internally connected together and must be connected to the external
+24Vdc supply’s common.
•The 7252 module uses the external +24Vdc supply to power the isolation circuitry and to generate +5Vdc user
power (pins 23 and 24). These two pins, which are internally connected together, can be used to power sensors
requiring less than 500 mA of current.
•Earth Grounds 1 through 4 (pins 1, 13, 14 and 19) are internally connected together and are connected to the
ControlLogix rack structure. The cable shields of the sensor’s cable should be connected to these terminals.
•Transducer signals are generally low voltage, low power signals. If you are using A-B guidelines for cabling
installation, treat the transducer cable as a Category 2 cable. It can be installed in conduit along with other low
power cabling such as communication cables and low power ac/dc I/O lines. It cannot be installed in conduit
with ac power lines or high power ac/dc I/O lines.
•Like all signal and communication cable, the transducer cable should be shielded. These shields must be
grounded only at one end of the cable. Because the rack cabinet is typically better grounded than the machine,
AMCI recommends that the cable shields be terminated at the 7252 module. However, if your cable shield is
attached to the sensor’s housing, and the sensor is grounded through its mounting, you must not connect the
cable shields to the 7252 module because this will create a ground loop.
•If a junction must be made in the signal cable, treat the shield as a signal-carrying conductor. Do not connect
the shield to ground at any junction box or the encoder/sensor.
•If the signal cable must cross power feed lines, it should do so at right angles.
•Route the cable at least five feet from high voltage enclosures, or sources of RF radiation.
Voltage
Regulator External Power
Supply
+24Vdc, pins 2 or 20 (connected together internally)
GND, pins 3,4,21,22)
+5Vdc out, pins 23, 24
+5Vdc
Optical isolation
+input data pins 9 or 10
-input, pins 11 or 12
7252 module

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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.

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3. PWM Mode 1 (Variable Pulse with External Interrogation) – 7252 Default Mode
In PWM Mode 3, the signal interface is a pulse-width modulated RS-422 signal. In this mode the 7252 module is
configured for external interrogation and generates a start pulse to begin measurement. This start pulse will be a
minimum of 1.0 microsecond in duration. Within 50 nanoseconds after the leading edge of the start pulse has been
received by the transducer, the LDT shall generate an output pulse with variable width. The duration of this output
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.
4. PWM Mode 2 (Variable Pulse with Internal Interrogation)
This mode is similar to PWM Mode 1, except that no interrogation from the 7252 module is needed. Instead, the LDT,
when powered, will continually output pulse width modulated signals. The duration of this output pulse is proportional
to the distance from the null zone to the magnet. The order of these pulses is illustrated in the following figure.
Recirculation
The recirculation method is used to improve the resolution of systems using digital LDT when the “on” time of a pulse width
output is multiplied by a specific factor. This multiplication provides more counting time for the counter in the module’s
electronics, thus improving the resolution.
The 7252 module does not use recirculations because it utilizes high-speed counters with enough resolution to ensure
accurate measurements.
LDT sensors connected to the 7252 must be set for Number of Recirculations = 1, if this is a settable parameter.

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Chapter 3: Programmable Parameters
The 7252 is configured by programming its Programmable Parameters. These parameters are broken down into three
groups, Module Setup, LDT Setup, and Data Setup parameters.
The 7252 uses two methods for the programming and monitoring of data. Input and Output registers are used to
program and monitor data that occurs on a regular schedule, such as reading the data value and status information or
setting the system time. Message instructions are used for operations that occur less frequently, such as programming
the module set up parameters or reading back the set up data for trouble shooting purposes.
Transducer Fault Latch - Transducer faults can be caused by improper wiring, electrical noise, or a damaged
transducer. When the unit detects a fault condition, it reports this fault over the backplane. Normally, a transducer fault
is not latched by the 7252 module and the Transducer Fault conditions will be cleared as soon as the 7252 module
detects valid LDT signals. If you have a situation where electrical noise is causing spurious transducer faults that you
can safely ignore, leave this parameter in its default condition. However, if you want to reliably capture these transient
faults, then you must enable the Transducer Fault Latch parameter. In this case, you must send a Clear Error command
to the 7252 module to clear the fault.
The default Transducer Fault Latch value is set to Self Clearing.
Count Direction: This parameter gives you the ability to reverse the direction of motion needed to increase the
position count. For simplicity’s sake, the two values for this parameter are called Positive Direction and Negative
Direction. When this parameter is set to its default of Positive, the Data Value is not changed. When this parameter is
set to Negative, the Data Value is multiplied by -1 before it is reported. For linear transducers, this has the effect of
reversing the direction of motion needed to increase the count. When using LDT’s and the Count Direction is set to
Positive, the Data Value usually increases as the magnet moves away from the head of the LDT. When the Count
Direction is set to Negative, the Data Value increases as the magnet moves towards the head of the LDT. You will
need probably need to Apply the Preset to the Data Value after you program the Count Direction parameter.
Velocity Update Time: The Velocity Update Time parameter sets the amount of time between Rate of Change
information updates to the PLC. Its can be set to either 60 milliseconds or 120 milliseconds, with 120 milliseconds
being the default. Decrease the time between updates for faster response to changes in this value. Increase the time
between updates for better averaging of this value. The Velocity update time does not affect the rate at which the
position data is updated.
The Velocity data is measured in Counts/Second. For example, if you have programmed the 7252 module for 0.001
inch resolution, and if the magnet is moving at a rate of two inches per second, then the 7252 module will report a
velocity value of 2000 counts / second.
Measurement Unit - Specifies the measurement unit for the Full Scale Length parameter and affects
the values that can be entered for Full Scale Count. This bit will indicate whether the unit of measurement is in inches
or mm (millimeters).
•When this bit is set to ‘1’, the position and velocity data is reported back in mm with a maximum resolution of
0.1mm
•When this bit is set to ‘0’, the unit of measurement will be reported back in inches with a maximum resolution
of 0.001 in
•The default Measurement Unit parameter is inches

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LDT Mode – Three Configuration Word bits are used to select the desired LDT mode, which can be one of the four
modes described in Chapter 2:
•Start/Stop Mode (default)
•Control Pulse Mode
•PWM Mode 1
•PWM Mode 2
LDT Gradient (Wire Speed) - This is a calibration parameter supplied by the LDT manufacturer and defines how fast
the pulse travels down the waveguide of the sensor. The data reported by the 7252 module will be repeatable, but not
accurate, if an incorrect Gradient value is used.
LDT manufacturers specify the gradient in µSec/inch, µsec/mm, or meters/second.
The gradient value used by the 7252 module has a range of 80000 to 99999, a default value of 90000 (for 9.0000
µsec/inch) and is always programmed in µsec/inch. Use the following formulas to convert from µsec/mm or
meters/second to µsec/inch.
Gradient in µsec/inch = (Gradient in µsec/mm * 25.4 mm/inch)
Gradient in µsec/inch = 1 / (Gradient in meters/sec * 0.00003937)
Full Scale Length - Most commonly set to the expected length of travel, the Full Scale Length can
actually be any value that simplifies the Full Scale Count value. Based on the Measurement Unit
setting, the range of values is 2 to 800 inches or 50 to 20320 millimeters. Default value of 16 inches.
Full Scale Count - Sets the number of counts over the specified Full Scale Length. The range of values
is 2 to (Full Scale Length * 1000) if Measurement Unit is inches or 2 to (Full Scale Length * 10) if
Measurement Unit is millimeters. Default value of 16000. (Resolution equals 0.001 inches)
Preset Value: The zero position of the LDT encoder’s Data Value may not match the zero position of the application
machine. The Preset Value parameter gives you the ability to offset the Data Value from the actual LDT data to a
value that will be more useful for your application.
Programming the Preset Value parameter does not change the Data Value. It is stored in the 7252 module’s
memory until the module sees a zero to one transition of the Apply Preset bit in the output registers.
Apply Preset: Offsetting the Data Value to the Preset Value is a two step operation. First, a Message Instruction must
be used to send the Preset Value with the other setup parameters to the 7252 module. Second, setting the Apply Preset
bit in the output registers will change the Data Value to the Preset Value.
Setting the Apply Preset bit causes the module to generate an internal offset value that is applied to the Data
Value before it is reported to the PLC. This internal offset is saved in the 7252 module’s Flash memory, so it is
not necessary to home the module at every power up. Please note that using a Message Instruction to program a
channel’s setup data will clear the internal offset generated by an Apply Preset operation.
The 7252 module’s Flash memory is guaranteed for 10,000 write cycles before
writing to it will cause it to fault. Therefore continuously applying the Preset should
be avoided. If your application requires you to continuously apply the Preset,
consider calculating and applying the Preset in your PLC program.

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Latched Input: The 7252 module has two Latch Inputs, one for each channel, that allow you to capture and display
the current Data Value whenever the input transitions. This parameter, which is composed of two bits, allows you to
capture the input on the 0 to 1 transition, the 1 to 0 transition, or on both transitions. The function of the Latched Input
will be disabled if neither bit is set.
To be read by the 7252 module, the latching inputs must be on for between 0.2ms and 1.2ms, depending on the
number of channels being used.
The 7252 module reports the status of the Latched input even if the function of the latched input has been
disabled.
The Latched Value is not saved through power down. Therefore, the Latched Value displayed in the 7252
module’s input registers at power up will be zero.
Limit Switch Position: These two-word parameters define ON and OFF setpoints. If the ON setpoint is less than the
OFF setpoint, a bit in the Input Registers, which can be easily interrogated by a relay instruction, will be set when the
Data Value is between these two setpoints, but not equal. If the ON setpoint is greater than then OFF setpoint, then the
bit will be set when the Data Value is outside of the these two setpoints, but not equal.
A separate Limit Switch bit based on the same ON/OFF setpoints also exists for the Interpolation Data Value.
Interpolated Data value: This additional and optional feature may be useful for customers using the ControlLogix
PLC’s virtual axis functionality. If used, the 7252 module will take the PLC’s Central System Clock-Time and the
sensor’s velocity data to calculate an Interpolated or “Look Ahead” Data value. This has two possible functions. One,
the Interpolated Data Value along with the time value can be sent to other ControlLogix modules, for example the
AMCI 8213-VA, allowing them to schedule their responses with a high degree of precision. Two, the Interpolated Data
Value allows the user to “Look Ahead” to what the Data Value will be at a defined time in the future. Here is the
procedure for generating the Interpolation Data Value.
1. Make the PLC the System Time Master by opening the Controller Properties and clicking
on the Date/Time tab. Click on the box next to the “Make this controller the Coordinated
System Time Master” text so that a check mark appears in the box and accept the changes
by clicking on OK. The Interpolated position value will be valid only if this step is
performed.
2. Create a GSV instruction in your ladder logic, with the Class Name set to CST and the
Attribute Name set to CurrentValue, to read the system time from the PLC. The
destination address must made up of two DINT registers.
3. If desired, add a value to word 0 of the time value read above. This value is entered in
1µs increments, every 1000 equals 1ms, and equals the amount of time that you want to
“look ahead.”
4. Place the time value from step 3 into the output registers. The next time that the
Interpolation Transmit bit transitions from either 0 to 1 or 1 to 0, the Central System Time
will be sent to the 7252 module.
5. The latest Interpolation Data Value will be located in the input data the next time the
module is updated at the normal RPI update.

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Chapter 4: Message Instructions
The programming of the 7252 module’s Setup data requires the use of Message Instructions. The format of this
instruction is shown below.
1. A different message instruction is needed for each channel of the 7252 module.
2. The message instruction sends data to or reads data from the 7252 module only when the rung transitions from
false to true.
3. The Message Control tag, message_ch1 in this example, used for Message Instruction Control must have the
MESSAGE data type.
4. Clicking on the button in the Message Instruction opens the Message Configuration Window, shown below. Enter
the appropriate data for the channel and operation being performed. When finished, click on the Apply button to
accept the new data.
Message Type: CIP Generic
Service Type: Must be Custom
Service Code: 4C to write data to the 7252 module, 4B to read data from the 7252 module
Class: Must be equal to 4.
Instance: Determined by the type of data being transferred, see the table below.
Attribute: Must be set to zero.
Source Element: If the Message Instruction is being used to send data to the 7252 module, then the source parameter
will be the first tag of the array that contains the data to be sent to the 7252 module.
If the Message Instruction is being used to read data from the 7252 module, than the source parameter
must be left blank.

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Source Length: If the Message Instruction is being used to send data to the 7252 module, then the Source Length
parameter must be equal to 28 bytes.
If the Message Instruction is being used to read data from the 7252 module, then the Source Length
Parameter must be set to zero.
Destination: If the Message Instruction is being used to send data to the 7252 module, then the Destination Parameter
must be left blank.
If the Message Instruction is being used to read data from the 7252 module, then the Destination
Parameter must be set to the first tag of the array where the data will be placed.
The Message Instruction is used with the following information to send Setup Data to the 7252 module.
LDT
Channel 1
SERVICE CODE 4C CLASS 4 Length in
[Bytes]
28
Used with assembly
instances 101, 102
INSTANCE 201 ATTRIBUTE 0
LDT
Channel 2
SERVICE CODE 4C CLASS 4 Length in
[Bytes]
28
Used with assembly
instance 102
INSTANCE 202 ATTRIBUTE 0
The Message Instruction is used with the following information to read Setup Data from the 7252 module.
LDT
Channel 1
SERVICE CODE 4B CLASS 4 Length in
[Bytes]
0
Used with assembly
instances 101, 102
INSTANCE 201 ATTRIBUTE 0
LDT
Channel 2
SERVICE CODE 4B CLASS 4 Length in
[Bytes]
0
Used with assembly
instance 102
INSTANCE 202 ATTRIBUTE 0

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Message Configuration – (Communication Tab)
When the Configuration window shown above is completed, click on the Communication tab. The following window
will open. Click on the Browse button and set the path parameter to the slot where the 7252 module is located. All of
the remaining Communication parameters can remain at their default settings.
Extended Error Codes
The Message Instructions used to send data to the 7252 module have an error register that can be used to obtain
diagnostic information from the module. This register’s address is user_tag.exerr. The following table shows the
values that will be displayed in this register if the data sent to the 7252 module is not valid.
Extended Error Codes
1 = Configuration Bits Word Format Error
•Reserved bits not equal to 0
•Selecting one of the reserved LDT mode types
2 = LDT Gradient Value is outside of its valid range of 80000 to 99999
3 = Full Scale Length is outside of its valid range of
2 to 800 if the units are in inches
50 to 20320 if the units are in millimeters
4 = Full Scale Count is outside of its valid range of
2 to (1000 * Full Scale Length) if the units are in inches
2 to (10 * Full Scale Length) if the units are in millimeters
10 = Trying to program channel 2 when the rack configuration has defined the 7252 as a
one channel module. (This will be displayed as 16#0000_000A)
•These error codes are only valid when register address user_tag.err is equal to 9.
•The Message Instructions Error bit and the Extended Error Code can only be cleared by sending valid data to
the 7252 module.

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Chapter 5: Setup Data
The message instructions described in chapter 4 above are used to send the setup data to the two channels of the
7252 module. This data consists of seven 32 bit words (28 bytes) shown in the following table. Each channel can
be programmed with different setup data.
Setup Data for the LDT Module
Data
Type Word Number
Function Range Factory Default
32-bit 0 Configuration Bits See description below 0
32-bit 1 LDT Gradient 80000 to 99999 90000
(9.0 µs/inch)
32-bit 2 Full Scale Length 2 to 800 inches or
50 to 20320 mm 16 inches
32-bit 3 Full Scale Count 2 to (1000 * Length in inches) or
2 * (Length in mm * 10) 16000
32-bit 4 Preset Value 0 to 16# FFFF_FFFF
-2,147,483,648 to +2,147,483,647 0
32-bit 5 Limit Switch ON-Position 0 to 16# FFFF_FFFF
-2,147,483,648 to +2,147,483,647 0
32-bit 6 Limit Switch OFF-Position 0 to 16# FFFF_FFFF
-2,147,483,648 to +2,147,483,647 0
All of the data must be present and valid when the message instruction is used to send the data to the 7252 module. If
the data is not valid, all of the data will be ignored, the message instruction’s error bit will be set, and the extended
error code will indicate exactly how the data is invalid. See chapter 3 for definitions of the set up parameters.
Configuration Bits:
Bits 0 to 7: Reserved, must be 0;
Bit 8: Transducer Fault Latch (0=self clearing, 1 = Latched Fault)
Bit 9: Program Count Direction (0 = Positive, 1 = Negative)
Bit 10: Program Velocity Update (0 = 160ms, 1 = 60ms)
Bit 11: Latch position on rising edge of input
Bit 12: Latch position on falling edge of input
Bit 13: Measurement Units (0=inches, 1=mm)
Bit 14 to 16: LDT Mode
Bit 16 Bit 15 Bit 14 LDT Mode
0 0 0 Start/Stop Mode (default)
0 0 1 Control Pulse Mode
0 1 0 PWM Mode 1
0 1 1 PWM Mode 2
1 0 0 reserved
1 0 1 reserved
1 1 0 reserved
1 1 1 reserved
.Bits 17.. 31: Reserved, must be 0;
Note 1: The Velocity Update Time does not affect the update of the Data Value.
Note 2: Programming a channel’s setup data will clear the internal offset generated by an Apply Preset Operation.

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Note 3: The 7252 module will accept and act on Setup Data sent from a Message Instruction that occurs in a Listen
Only Processor.
Note 4: The gradient value is entered with an assumed decimal point. For example, a gradient of 9.1234 would be
entered as 91234. Zeros must be entered in any unused places. For example, a gradient of 9.12 would be
entered as 91200.
Note 5: The 7252 will power up and immediately start sampling the channels. It will either use the Setup Data Words
0-6 (page 17) from the Flash memory, or if there is none present, it will use their default values (out-of-the-box
state).
Chapter 6: Reading Status Data
The message instructions described in Chapter 4 above can be used to read the current setup data from each of
channels of the 7252 module. This status data consists of eight 32 bit words. The destination address must be made up
of a tag array that is at least eight DINT words long.
Please note that it is possible to read only valid data from the 7252 module. The module does not store any Setup Data
that caused the Message Instruction’s Error bit to be set.
Reading Data from the LDT Module
Data
Type Word Number
Function
32-bit 0 Configuration Bits
32-bit 1 LDT Gradient
32-bit 2 Full Scale Length
32-bit 3 Full Scale Count
32-bit 4 Preset Value
32-bit 5 Limit Switch ON-Position
32-bit 6 Limit Switch OFF-Position
32-bit 7 Internal Offset generated by an Apply Preset operation
Configuration Bits:
Bits 0 to 7: Reserved, will be 0;
Bit 8: Transducer Fault Latch (0=self clearing, 1 = Latched Fault)
Bit 9: Program Count Direction (0 = Positive, 1 = Negative)
Bit 10: Program Velocity Update (0 = 160ms, 1 = 60ms)
Bit 11: Latch position on rising edge of input
Bit 12: Latch position on falling edge of input
Bit 13: Measurement Units (0=mm, 1=inches)
Bit 14 to 16: LDT Mode
Bit 16 Bit 15 Bit 14 LDT Mode
0 0 0 Start/Stop Mode
0 0 1 Control Pulse Mode
0 1 0 PWM Mode 1
0 1 1 PWM Mode 2
1 0 0 reserved
1 0 1 reserved
1 1 0 reserved
1 1 1 reserved
Bits 17.. 31: Reserved, will be 0;

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Chapter 7: Input & Output Data
Input Registers: (Data sent from the 7252 module to the PLC)
The input data consists of five (for 1 channel) or ten (for 2 channels) 32-bit words, and is read by the PLC at the RPI
(Requested Packet Interval) Time that is asynchronous to the Ladder Logic Program. The Input data will be referenced
as Local:X.I.Data[Y] where “X” is the slot number and “Y” is the word number.
To ensure that the same data is used throughout the entire PLC program, this data should be buffered to internal
registers at one place in the program. However, in order to take advantage of the real time availability of the
Interpolation Data value, the Interpolation Acknowledge bit, the Limit Switch State Bit, and the Interpolation Limit
Switch State Bit should be used directly from their respective Input Registers.
The data contained in the input registers consists of Status Word, Data Value, Velocity and any associated Latched or
Interpolated Data Values.
Input Data for the 1 Channel Configuration
Channel
Number 32 Bit Word Function Units
1
0 Status Word1 See descripiton below
1 Data Value 1 Counts
2 Velocity 1 Counts / Second
3 Latched Data Value 1 Counts
4 Interpolated Data Value 1 Counts
Input Data for the 2 Channel Configuration
Channel
Number 32 Bit Word Function Units
1
0 Status Word 1 See descripiton below
1 Data Value 1 Counts
2 Velocity 1 Counts / Second
3 Latched Data Value 1 Counts
4 Interpolated Data Value 1 Counts
2
5 Status Word 2 See descripiton below
6 Data Value 2 Counts
7 Velocity 2 Counts / second
8 Latched Data Value 2 Counts
9 Interpolated Data Value 2 Counts

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Description of the Status Word:
Bit 0: APPLY PRESET ACKNOWLEDGE: This bit will be set when the corresponding Apply Preset Command bit
is set in the output registers.
Bit 1: INTERPOLATION ACKNOWLEDGE: This bit will be set when the corresponding Interpolation Command
bit is set in the output registers, after carrying out the INTERPOLATION operation.
Bit 2: VELOCITY AT ZERO: Set when there has been no motion for the last portion of the Velocity Update Time.
Bit 3: MOTION DIRECTION: Set when data value is decreasing. The bit remains in the last state when there is no
motion.
Bit 4: LATCHING INPUT: Set when the latching input for respective channel is receiving power. This bit will be
set to indicate that the input is active even if the function of the input has been disabled by the channel’s
programming.
Bit 5: LIMIT SWITCH STATE: Set when the data value is between the programmed Limit Switch ON- and OFF-
Setpoints.
Bit 6: INTERPOLATION LIMIT SWITCH STATE: Set when the interpolated data value is between the
programmed Limit Switch ON- and OFF-Setpoints. This bit will only be updated on the 0 to 1 or 1 to 0
transitions of the Interpolation Command Output bit.
Bit 7: TRANSDUCER FAULT: This bit will be set to indicate one of the following conditions.
By default, transducer fault errors will be removed as soon as the problem has been corrected. However, if
the 7275 module has been programmed for Transducer Fault Latch, this bit will remain set until the Clear
Latched Transducer Faults command has been sent from the Output Registers. Cycling power to the module
will also clear a Latched Transducer Fault.
Bits 8 to 13: Reserved for future use
Bit 14: OUTPUT FAULT: Set when one or more of the bits in the corresponding COMMAND WORD are set.
This bit will be automatically reset when the incorrect bit(s) are reset.
Bit 15: BAD CRC Memory Error: Set when the flash area for the corresponding channel parameters shows corrupt
data. It will still be possible to use the 7252, but the module will power up using its default parameters.
That is, you will have to use message instructions to program your setup data at every power up. If you do
not want to use the module in this way, it must be returned to AMCI for repair.
Bits 16 to 31: Reserved for future use
•
Broken Transducer cable
•Improperly wired cable
•Non-compatible transducer
•Magnet is not on the sensor
•Magnet is on the sensor but outside of the usable range
•External Power supply not attached to both the 7252 module and
the sensor