Screed ECM
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| Illustration 1 | g01389775 |
The AS3251C Screed is equipped with an onboard computer that is called an electronic control module (ECM). The screed ECM is located under the top step of the screed.
The ECM has two 70-pin connectors. Connector "J1" (1) is on the right and connector "J2" (2) is on the left. The screed ECM receives input signals from switches and sensors on the screed and other ECMs that are on the machine which monitor current operating conditions. System software compares the gathered input to information that is stored in the computer's memory. The software evaluates the current conditions and the software generates an appropriate output signal.
The screed ECM works in conjunction with the right and left operator control units and the machine ECM in order to control the material feed system. The ECMs on the screed and the machine communicate through two bidirectional data links, the Controller Area Network (CAN) and the CAT Data Link (CDL). The CDL may be used as a backup in case the CAN network becomes nonfunctional. The CDL is a proprietary communication standard developed by Caterpillar Inc.
Input and Output Terminals
Connector "J1"
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| Illustration 2 | g01389782 |
When the electrical disconnect switch is in the ON position, power transfers from the screed ECM circuit breaker to terminal "J1-31" and to terminal "J1-39" of the screed ECM. This voltage input provides the power for the processor. When the main power relay is energized, power transfers from the screed circuit breaker to terminal "J1-1" of the screed ECM. This voltage input provides the wakeup signal to the screed ECM. The screed ECM is grounded at terminal "J1-23".
Input Components
The ECM monitors input signals through connector "J1" from the following components in the material feed system:
- Left feeder mode switches ("J1-27", "J1-28", "J1-32", and "J1-33")
- Right feeder mode switches ("J1-34", "J1-35", "J1-40", and "J1-41")
- Left material height dial ("J1-22")
- Right material height dial ("J1-29")
- Vibratory motor speed dial ("J1-30")
- Washdown mode switch ("J1-26")
Left Feeder Mode Switch (Left Main Panel)
The ECM simultaneously monitors the condition of the circuit at terminal "J1-27" and the circuit at terminal "J1-28" in order to determine the position of the left feeder mode switch on the left main panel. When the circuit at terminal "J1-27" is floating and the circuit at terminal "J1-28" is grounded, the ECM determines that the left feeder mode switch is in the OFF position. When the circuit at terminal "J1-27" is grounded and the circuit at terminal "J1-28" is floating, the ECM determines that the left feeder mode switch is in the OVERRIDE position. When the circuit at terminal "J1-27" is floating and the circuit at terminal "J1-28" is floating, the ECM determines that the left feeder mode switch is in the AUTO position.
Left Feeder Mode Switch (Left Extender Panel)
The ECM simultaneously monitors the condition of the circuit at terminal "J1-32" and the circuit at terminal "J1-33" in order to determine the position of the left feeder mode switch on the left extender panel. When the circuit at terminal "J1-32" is floating and the circuit at terminal "J1-33" is grounded, the ECM determines that the left feeder mode switch is in the OFF position. When the circuit at terminal "J1-32" is grounded and the circuit at terminal "J1-33" is floating, the ECM determines that the left feeder mode switch is in the OVERRIDE position. When the circuit at terminal "J1-32" is floating and the circuit at terminal "J1-33" is floating, the ECM determines that the left feeder mode switch is in the AUTO position.
Right Feeder Mode Switch (Right Main Panel)
The ECM simultaneously monitors the condition of the circuit at terminal "J1-34" and the circuit at terminal "J1-35" in order to determine the position of the right feeder mode switch on the right main panel. When the circuit at terminal "J1-34" is floating and the circuit at terminal "J1-35" is grounded, the ECM determines that the left feeder mode switch is in the OFF position. When the circuit at terminal "J1-34" is grounded and the circuit at terminal "J1-35" is floating, the ECM determines that the left feeder mode switch is in the OVERRIDE position. When the circuit at terminal "J1-34" is floating and the circuit at terminal "J1-35" is floating, the ECM determines that the left feeder mode switch is in the AUTO position.
Right Feeder Mode Switch (Right Extender Panel)
The ECM simultaneously monitors the condition of the circuit at terminal "J1-40" and the circuit at terminal "J1-41" in order to determine the position of the right feeder mode switch on the right extender panel. When the circuit at terminal "J1-40" is floating and the circuit at terminal "J1-41" is grounded, the ECM determines that the left feeder mode switch is in the OFF position. When the circuit at terminal "J1-40" is grounded and the circuit at terminal "J1-41" is floating, the ECM determines that the left feeder mode switch is in the OVERRIDE position. When the circuit at terminal "J1-40" is floating and the circuit at terminal "J1-41" is floating, the ECM determines that the right feeder mode switch is in the AUTO position.
Left Material Height Dial
The ECM monitors the voltage of the circuit at terminal "J1-22" in order to determine the position of the left material height dial on the left main panel. When the voltage at terminal "J1-22" is approximately 1.75, the ECM determines that the left material height dial is in the MIN position. When the voltage at terminal "J1- 22" is approximately 3.25, the ECM determines that the left material height dial is in the MAX position. The dial factor will be linear between these two positions. The dials minimum and maximum calibration points will be automatically updated whenever the dial value goes beyond the saved minimum and maximum calibration values.
Right Material Height Dial
The ECM monitors the voltage of the circuit at terminal "J1-29" in order to determine the position of the right material height dial on the right main panel. When the voltage at terminal "J1-29" is approximately 1.75, the ECM determines that the right material height dial is in the MIN position. When the voltage at terminal "J1-29" is approximately 3.25, the ECM determines that the right material height dial is in the MAX position. The dial factor will be linear between these two positions. The dials minimum and maximum calibration points will be automatically updated whenever the dial value goes beyond the saved minimum and maximum calibration values.
Vibratory Motor Speed Dial
The ECM monitors the voltage of the circuit at terminal "J1-30" in order to determine the position of the vibratory motor speed dial. When the voltage at terminal "J1-30" is approximately 1.75, the ECM determines that the vibratory motor speed dial is in the MINIMUM position. When the voltage at terminal "J1-30" is approximately 3.25, the ECM determines that the vibratory motor speed dial is in the MAXIMUM position. The dial factor will be linear between these two positions. The dial's minimum and maximum calibration points will be automatically updated whenever the dial value goes beyond the saved minimum and maximum calibration values.
Washdown Mode Switch
The washdown mode switch is a momentary switch that is used to enable the washdown system and to disable the washdown system. The ECM monitors the condition of the circuit at terminal "J1-26" in order to determine the position of the washdown mode switch. When the circuit at terminal "J1-26" is grounded, the ECM will toggle the washdown pump either ON or OFF. This will be opposite of the pump's current state. When the circuit at terminal "J1-26" is floating, the ECM determines that the washdown mode switch is in the HOLD position.
Connector "J2"
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| Illustration 3 | g01389791 |
When the main power relay is energized, power transfers from the screed circuit breaker to terminal "J2-1" of the screed ECM. This voltage input provides the wakeup signal to the screed ECM.
Controller Area Network (CAN)
The CAN requires a positive (high speed) line and negative (low speed) line. The screed ECM has two sets of CAN lines. The positive lines are connected to terminals "J2-56" and "J2-67" of the screed ECM. The negative lines are connected to terminals "J2-68" and "J2-70" of the screed ECM. The set of CAN lines that are connected to terminal "J2-56" and terminal "J2-68" are connected to the Asphalt Paver harness. The set of CAN lines that are connected to terminal "J2-67" and terminal "J2-70" are connected to the control unit for the screed heater.
Cat Data Link (CDL)
The CDL requires a positive line and a negative line. The positive line is connected to terminal "J1-10" of the screed ECM. The negative line is connected to terminal "J1-20" of the screed ECM.
Input Components
The ECM monitors input signals through connector "J2" from the following components in the material feed system:
- Right material height sonic sensor ("J2-24")
- Left material height sonic sensor ("J2-25")
- Left material height sensor input (paddle or sonic) ("J2-26")
- Right material height sensor input (paddle or sonic) ("J2-27")
- Left screed extender switches ("J2-31", "J2-36", "J2-46", and "J2- 47")
- Right screed extender switches ("J2-37", "J2-38", "J2-54", and "J2- 55")
ECM Software and Material Height Sonic Sensors
The ECM software contains the two duty cycle points (0 percent and 100 percent) needed to map the sonic sensor inputs. One duty cycle point will be for the full on position of the sensor (32 inch away) and the other will be for the full off position of the sensor (12 inch away). These two duty cycle points will be adjustable in the software in order to compensate for a sensor that has different on and off points. The sonic position will be linear between the full off and full on calibrations before scaling.
Right Material Height Sonic Sensor
The ECM monitors the duty cycle of the left sonic sensor at terminal "J2-24". When the duty cycle at terminal "J2-24" drops to less than 2 percent, the ECM will not allow the feeder system to function in the automatic mode. When the duty cycle at terminal "J2-24" reaches the 94 percent to the 98 percent range, the ECM will determine the left material height sensor is out of range and alert the operator. When the duty cycle at terminal "J2-24" is greater than 98 percent, the ECM will not allow the feeder system to function in the automatic mode.
Left Material Height Sonic Sensor
The ECM monitors the duty cycle of the left sonic sensor at terminal "J2-25". When the duty cycle at terminal "J2-25" drops to less than 2 percent, the ECM will not allow the feeder system to function in the automatic mode. When the duty cycle at terminal "J2-25" reaches the 94 percent to the 98 percent range, the ECM will determine the left material height sensor is out of range and alert the operator. When the duty cycle at terminal "J2-25" is greater than 98 percent, the ECM will not allow the feeder system to function in the automatic mode.
Left Material Height Sensor Input (Sonic/Paddle)
The ECM monitors the condition of the circuit at terminal "J2-26" in order to determine the type of material height sensor input being used on the left side of the machine. When the circuit at terminal "J2-26" is grounded, the ECM determines that the left material height sensor input is a sonic sensor. When the circuit at terminal "J2-26" is floating, the ECM determines that the left material height sensor input is a paddle sensor.
Right Material Height Sensor Input (Sonic/Paddle)
The ECM monitors the condition of the circuit at terminal "J2-27" in order to determine the type of material height sensor input being used on the right side of the machine. When the circuit at terminal "J2-27" is grounded, the ECM determines that the right material height sensor input is a sonic sensor. When the circuit at terminal "J2-27" is floating, the ECM determines that the right material height sensor input is a paddle sensor.
Left Screed Extender Switch (Left Main Panel)
The ECM simultaneously monitors the condition of the circuit at terminal "J2-31" and the circuit at terminal "J2-36" in order to determine the position of the left screed extender switch on the left main panel. When the circuit at terminal "J2-31" is floating and the circuit at terminal "J2-36" is floating, the ECM determines that the left screed extender switch is in the HOLD position. When the circuit at terminal "J2-31" is grounded and the circuit at terminal "J2-36" is floating, the ECM determines that the left screed extender switch is in the RETRACT position. When the circuit at terminal "J2-31" is floating and the circuit at terminal "J2-36" is grounded, the ECM determines that the left screed extender switch is in the EXTEND position.
Left Screed Extender Switch (Left Extender Panel)
The ECM simultaneously monitors the condition of the circuit at terminal "J2-46" and the circuit at terminal "J2-47" in order to determine the position of the left screed extender switch on the left extender panel. When the circuit at terminal "J2-46" is floating and the circuit at terminal "J2-47" is floating, the ECM determines that the left screed extender switch is in the HOLD position. When the circuit at terminal "J2-46" is grounded and the circuit at terminal "J2-47" is floating, the ECM determines that the left screed extender switch is in the RETRACT position. When the circuit at terminal "J2-46" is floating and the circuit at terminal "J2-47" is grounded, the ECM determines that the left screed extender switch is in the EXTEND position.
Right Screed Extender Switch (Right Main Panel)
The ECM simultaneously monitors the condition of the circuit at terminal "J2-37" and the circuit at terminal "J2-38" in order to determine the position of the right screed extender switch on the right main panel. When the circuit at terminal "J2-37" is floating and the circuit at terminal "J2-38" is floating, the ECM determines that the right screed extender switch is in the HOLD position. When the circuit at terminal "J2-37" is grounded and the circuit at terminal "J2-38" is floating, the ECM determines that the right screed extender switch is in the RETRACT position. When the circuit at terminal "J2-37" is floating and the circuit at terminal "J2-38" is grounded, the ECM determines that the right screed extender switch is in the EXTEND position.
Right screed extender switch (Right Extender Panel)
The ECM simultaneously monitors the condition of the circuit at terminal "J2-54" and the circuit at terminal "J2-55" in order to determine the position of the right screed extender switch on the right extender panel. When the circuit at terminal "J2-54" is floating and the circuit at terminal "J2-55" is floating, the ECM determines that the right screed extender switch is in the HOLD position. When the circuit at terminal "J2-54" is grounded and the circuit at terminal "J2-55" is floating, the ECM determines that the right screed extender switch is in the RETRACT position. When the circuit at terminal "J2-54" is floating and the circuit at terminal "J2-55" is grounded, the ECM determines that the right screed extender switch is in the EXTEND position.
Output Components
The ECM transmits output signals through connector "J2" for the following components in the material feed system:
- Left extender solenoids (extend/retract)
- Right extender solenoids (extend/retract)
- Washdown lamp
Screed Extender Solenoids
The screed extender solenoids are on/off solenoids used to control the screed extenders. These solenoids are activated by output signals from the ECM. The ECM will enable the proper extender solenoid based on the screed extender switch input.
The ECM transmits a signal at terminal "J2-2" in order to activate the left screed extend solenoid.
The ECM transmits a signal at terminal "J2-6" in order to activate the left screed retract solenoid.
The ECM transmits a signal at terminal "J2-5" in order to activate the right screed extend solenoid.
The ECM transmits a signal at terminal "J2-7" in order to activate the right screed retract solenoid.
Washdown Lamp
The ECM will transmit a signal at terminal "J2-9" in order to activate the washdown lamp when the washdown pump is on.