723PLUS Digital Speed Control Caterpillar

Introduction

This section contains information on calibrating of the control. This section includes initial settings and adjustments for the start-up. These adjustments are intended to allow starting the engine for the first time.

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The engine may overspeed due to incorrect assembly or adjustment. Engine overspeed could result in personal injury, loss of life and/or property damage. Be prepared to stop the engine by activating the engine shutdown system or closing the air inlet lines.

Start-up Adjustments

1. Complete the installation checkout procedure in this Service Manual, "Installation" and review the settings of the menu in this Service Manual, "Programmable Parameters". Ensure that all critical set points are correct. This includes the following items in "Configure" menu: "CFIG OPTION" and "CFIG SPEED CONTROL". This also includes the following items in the "Service" menu: "1st DYNAMICS", "2nd DYNAMICS" and "SPEED SETTING". All other menu items that are critical to the specific application must also be determined and correctly set.

2. Open the "Open to Run" contact. Be sure that the "Rated Speed" contact is in the idle position. This is the open position. Apply power to the control. Do not proceed unless the green "POWER OK" and "CPU OK" indicators on the front of the control are on.

3. Check the speed sensor.

   Under the following conditions, the red "FAILED SPD SENSOR" will be activated:

   • the rpm of the engine is less than 5 percent of the rated rpm.

   • the amplitude of the speed sensor is less than 1.5 Vrms.

   Note: Before cranking, be sure to prevent the engine from starting.

   Measure the voltage while you are cranking. The minimum voltage that is required from the speed sensor to operate the control is 1.5 Vrms.

   If the red "FAILED SPD SENSOR 1" indicator remains on, shut down the engine.

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Accidental engine starting can cause injury or death to personnel. To prevent accidental engine starting, turn the ignition switch to the OFF position, place a do not operate tag at the ignition switch location and disconnect and tape the electrical connection to the stop solenoid that is located on the fuel injection pump.

4. Start the engine.

   If there is not enough fuel for starting the engine, increase the "Start Fuel Limit". This is in the "Fuel Limiters" menu. The control will reduce the fuel when the speed setting is reached. The control requires extra fuel to accelerate the engine to idle speed. The control may take a few starts in order to determine the final setting of the "Start Fuel Limit".

   Increase the "Start Fuel Limit" and/or the "Start Ramp Rate" if the start time is excessive.

   Decrease the "Start Fuel Limit" and/or the "Start Ramp Rate" if the start time is too fast. To determine the final setting of the control, start the engine when the engine is hot and also cold.

5. Adjust for stable operation.

   If the engine is hunting at a rapid rate, slowly decrease the "Gain" until performance is stable.

   If the engine is hunting at a slow rate, increase the "Reset" value.

   If increasing the "Reset" value does not stabilize the engine, you may need to make one of the following adjustments:

   • Slowly decrease the "Gain OR" setting.

   • Slowly decrease the "Gain" setting.

   • Increase the "Compensation" setting.

This will complete the adjustment of the start-up. Save the settings at this time by pressing the "SAVE" key on the programmer or by saving settings with the Control View or the Watch Window. The programmer will display the "Saving Changes" message. The Control View or the Watch Window have a box that appears. This box will tell you that the values have been saved.

Dynamic Adjustments

The purpose of the dynamic adjustment is for optimum performance from the engine from minimum "Speed/Load" to full speed and load. Apply all of the adjustments to the "1st Dynamics" and the "2nd Dynamics". When the "1st Dynamics" are adjusted the contacts of the "2nd Dynamics" will be open. When the "2nd Dynamics" are adjusted the contacts of the "2nd Dynamics" will be closed.

Do the following adjustments first for the "1st Dynamics". Use the "1st Dynamics Menu" to set the "1st dynamics" if changes are needed.

Then repeat the adjustments for "2nd Dynamics". Use the "2nd Dynamics Menu" to set the "2nd Dynamics", if changes are needed.

1. No Load Adjustment

   1. Do this adjustment when the load is not applied.

   2. Slowly increase the "Gain" set point until the engine becomes slightly unstable. Then reduce the "Gain" in order to stabilize the engine.

   3. Record the "Fuel Demand" that is read on the "Display Menu" when the performance at no load is acceptable. Set the "Gain Slope Breakpoint" to this reading. Observe the movement of the actuator. If the activity of the actuator is excessive, reduce the "Gain" set point slightly in order to get the movement of the actuator to a level that is acceptable.

   4. There are two possible causes of slow periodic cycling of the engine speed out of range from the speed setting:
      • The "Gain" is set too high and the "Reset" is set too low. Reduce the "Gain" by 50 percent and increase the "Reset" slightly. For example, if the "Gain" is set at 0.02 reduce the value to 0.01. Observe the movement of the actuator. Continue to increase the "Reset" until the movement is acceptable but not excessive. A final value of the "Reset" should be between 1.0 and 2.0 for most large engines. If the "Reset" value exceeds 2.0 increase the "Compensation" set point by 50 percent and repeat the procedure. This procedure will continue to improve the performance.

      • The "Gain" is set too low. If the above procedure does not improve the cycling of the engine speed the control may be limiting the cycling that is set by the "Window Width" set point. Increase the "Gain" set point in order to minimize the cycling. If the movement of the actuator becomes excessive, reduce the "Compensation" set point until the movement is acceptable. In some cases, "Compensation" may be reduced to zero and only the "Gain" and the "Reset" adjustments may be used. If necessary, eliminate excessive response of the actuator to misfiring or other periodic disturbances. Reduce the "Window Width" set point until the cycle is acceptable without excessive movement of the actuator.

2. Full Load Adjustment

   1. Make these adjustments when the engine is at the speed and the load of normal operation.

   2. If operation in this range is satisfactory, no further dynamic adjustments are necessary. If excessive errors in speed occur during changes in load or a bump of the actuator, increase the "Gain Slope" adjustment until the performance of the engine is satisfactory. Refer to Illustration 1. If movement of the actuator is still excessive, then perform step 3. Then repeat step 2.b. If hunting still occurs for a long period of time after a change in load, reduce the "Reset" set point slightly and increase the "Gain" slightly. If hunting occurs after a change in load but decreases or stops in time, increase the "Reset" set point slightly and reduce the "Gain" set point. Refer to Illustration 2.

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Illustration 1	g00677749

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Illustration 2	g00677751

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NOTICE
The use of negative Gain Slope should be considered carefully. Low gain at high fuel levels results in poor load rejection response and possible overspeed. The maximum fuel limit must be set near the full load output current demand to prevent excessive integrator windup and a subsequent low gain condition.

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The engine may overspeed due to incorrect assembly or adjustment. Engine overspeed could result in personal injury, loss of life and/or property damage. Be prepared to stop the engine by activating the engine shutdown system or closing the air inlet lines.

3. The control should automatically change to high gain in order to reduce the amplitude of the error in speed when a significant change in load occurs. Decrease or increase the "Window Width" set point, so that the set point is just greater than the magnitude of the acceptable error in speed. A value of the "Gain Ratio" that is too high will cause the control to hunt through the region of the low gain. This will normally occur when the "Window Width" is set too low. If necessary, decrease the "Window Width" in order to control the limit of cycling. The "Gain Ratio" may be reduced for operations that are more stable. Refer to Illustration 3.

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Illustration 3	g00677748

4. Verify that the performance is satisfactory at all speeds and load conditions. Repeat Step 3, if necessary. Testing the full load rejection is recommended as part of testing performance.

5. While the engine is operating at full load, record the "Actuator Output" that is on "Display Menu 1". Select the "Maximum Fuel Limit" set point on the "Fuel Limiter Menu". Set the setpoint at approximately 10 percent over the output for full load, if you desire. Otherwise leave the setpoint at 100 percent.

Check the operation of a start-up when the engine is hot and cold in order to obtain the optimum stability under all conditions.

Torsional Adjustments

The Torsional Level is determined by the instantaneous difference in speed between the two speed sensors. The difference in speed is an indication of the energy that is stored or released by the flexible coupling. There are two separate functions which can occur with the Torsional Level. The "Torsional Filter" function will filter the two speed signals. The "Torsional Filter" will provide a signal to the "Speed Filter" function and to the PID which will reduce the speed change that is caused by the flexible coupling. This function is adjusted by the value of item "ENG SENSOR WEIGHT" in the "TORSIONAL FILTER" menu. The "Torsional Limit" function will provide a temporary maximum limit to the "Fuel Demand". This limit is adjusted with item "TORSNL FUEL LIMIT". The temporary limit is set if the "Torsional Level" exceeds the value that is adjusted by the item "TORSNL LEVEL @LIMIT". The limit is removed when the "Torsional Level" is reduced below the value that is adjusted by the item "TORSNL LEVEL @CLEAR".

1. Set the "ENG SENSOR WEIGHT" with the following procedure. The "Torsional Level" is the ratio that is between the inertia of the engine and the inertia of the system.

   1. If you know the values then set the initial value of the "Engine Sensor Weight". The value is equal to the inertia of the engine that is divided by the quantity and the following procedure that is outlined below. The quantity is equal to the inertia of the engine plus the inertia of the driven equipment.

   2. If you do not know the values of the system, then start with the default value and follow the procedure that is outlined below.

2. It is important to know the speed and/or load that will cause the system to go into torsional instability. This is referred to here as the torsional point. The torsional point can be found by bumping the system by using the "Actuator Bump" function that is in the dynamic menus. Move the system away from the torsional point if the torsional point becomes unstable. Bump the system at several different speeds and loads.

   1. If the system remains stable, slightly increase the dynamic Gain and again bump the system at several different speeds and loads. A torsional oscillation may occur at some point which can be corrected with the "Engine Sensor Weight". Reduce the value by a small amount. Approach the torsional point after each adjustment. Check the performance and determine if the performance is improving or degrading.

   2. If the performance is improving, continue making small reductions until you find the value that requires no further improvements.

   3. If the performance is getting worse, begin increasing the value above the initial "Engine Sensor Weight". You must determine if any improvement is observed.

   4. If the performance is improving, continue making small increases until you find the value that produces no further improvements.

      Be sure to return the "Dynamic Gain" setting to the proper value.

3. "TORSNL FUEL LIMIT" can be adjusted by finding the torsional point and reducing the limit to a point that will eliminate the "Fuel Demand" oscillations or the oscillation will be reduced to a safe level.

   1. Set the item "TORSNL LEVEL @LIMIT" to 0.00 to activate the limit.

   2. Monitor the item "TORSNL FILTER ACTIVE" in the "Display Ctrl Mode" and be sure that the limit is active.

   3. Monitor the item "TORSIONAL LEVEL (%RPM)" in the "Display Menu" and go to the torsional point. Record the value of the "TORSIONAL LEVEL".

   4. Reduce the value of the "TORSNL FUEL LIMIT" in the "Torsional Filter Menu" and eliminate the "Fuel Demand" oscillations.

      Once the oscillations are reduced sufficiently again record the value of the "TORSIONAL LEVEL(%RPM)".

4. "TORSNL LEVEL @LIMIT" can be adjusted to the reading that is recorded above for the "TORSIONAL LEVEL".

5. "TORSNL LEVEL @CLEAR" can be adjusted to the reading that is recorded above for the "TORSIONAL LEVEL".

Note: The "Torsional Limit" function may not be required if the "Torsional Filter" function can reduce oscillations sufficiently. When the engine is operating at the torsion point this situation is preferred because the load will not be affected.

Adjusting the Fuel Limiters

Fuel limiters will limit the demand for fuel during various conditions.

"Start Fuel Limit" sets the maximum "Fuel Demand" when the engine is starting and the engine speed is below idle. The limit is usually set at the fuel level that is required to start the engine. The fuel level is usually greater than the "Fuel Demand" at "Idle Speed" and the fuel level is less than 100 percent of the "Fuel Demand".

1. Reduce the value of item "START FUEL LIMIT(%FD)" in menu "FUEL LIMITERS" and start the engine. Repeat this step until the engine no longer starts satisfactorily. The item "ON START LIMIT (LSS)" in the "DISPLAY CTRL MODE" menu can be monitored in order to determine when the "Start Limiter" is limiting the "Fuel Demand".

2. "Start Ramp Rate" will enable you to set the amount for the "Start Fuel Limit" to increase while the engine is cranking. The final adjustment should be made on a cold day when the normal starting "Fuel Demand" will be insufficient to start the engine. A start-up that is satisfactory can be obtained by increasing the "Start Ramp Rate".

3. "Maximum Fuel Limit" will enable you to set the maximum "Fuel Demand". Adjust so that all loads and transients can be satisfactorily assumed. Hot days may require more fuel for the engine to operate at full load.

Speed Adjustments

Adjustment of the references for speed should not require further setting as the references are precisely determined. However, the "Remote Speed Setting" input involves an analog circuit that may require adjustment.

"4 to 20 mA Remote Speed Setting Input"

1. Apply 4 mA to the "Remote Speed Setting Input". Be sure that the remote operation has been selected. Close the contact of the "Raise Speed" and the "Lower Speed". If the engine rpm is not at desired speed, then increase or decrease the 4 mA "Remote Reference" set point until the correct speed is achieved. There may be a small difference between the set point and actual speed which compensates for the inaccuracies in the analog circuits.

2. Now apply 20 mA to the "Remote Speed Setting Input". Wait until the ramp stops. Increase or decrease the 20 mA "Remote Reference" set point until the desired engine rpm is reached. the engine rpm desired.

3. Repeat the above steps until the speeds at 4 mA and 20 mA are within your required range.