2–30

Using the Front Panel Keypad

Inverter Mounting

and Installation

 

 

10

Powerup Test Observations and Summary

Step 10: Reading this section will help you make some useful observations when first running the motor.

Error Codes - If the inverter displays an error code (LED format is “E X X”), see “Monitoring Trip Events, History, & Conditions” on page 6–5 to interpret and clear the error.

Acceleration and Deceleration - The SJ300 inverter has programmable acceleration and deceleration values. The test procedure left these at the default value, 10 seconds. You can observe this by setting the potentiometer at about half speed before running the motor. Then press RUN, and the motor will take 5 seconds to reach a steady speed. Press the STOP key to see a 5 second deceleration to a stop.

State of Inverter at Stop - If you adjust the motor’s speed to zero, the motor will slow to a near stop, and the inverter turns the outputs OFF. The high-performance SJ300 can rotate at a very slow speed with high torque output, but not zero (must use servo systems with position feedback for that feature). This characteristic means you must use a mechanical brake for some applications.

Interpreting the Display - First, refer to the output frequency display readout. The maximum frequency setting (parameter A004) defaults to 50 Hz or 60 Hz (Europe and United States, respectively) for your application.

Example: Suppose a 4-pole motor is rated for 60 Hz operation, so the inverter is configured to output 60 Hz at full scale. Use the following formula to calculate the RPM.

RPM =

Frequency---------------------------------------⋅ 60-

=

Frequency------------------------------------------⋅ 120-

=

60--------------------⋅ 120

= 1800RPM

 

Pairs of poles

 

# of poles

 

4

 

The theoretical speed for the motor is 1800 RPM (synchronous speed). However, an induction motor cannot generate torque unless its shaft turns at a slightly different speed. This difference is called slip. So it’s common to see a rated speed of approximately 1750 RPM on a 60 Hz, 4- pole motor. Using a tachometer to measure shaft speed, you can see the difference between the inverter output frequency and the actual motor speed. The slip increases slightly as the motor’s load increases. This is why the inverter output value is called “frequency,” since it is not exactly equal to motor speed. You can program the inverter to display output frequency in units more directly related to the load speed by entering a constant (discussed more in depth on

page 3–41).

Run/Stop Versus Monitor/Program Modes – The Run LED on the inverter is ON in Run Mode, and OFF in Stop Mode. The Program LED is ON when the inverter is in Program Mode, and OFF for Monitor Mode. All four mode combinations are possible. The diagram to the right depicts the modes and the mode transitions via keypad.

STOP

RESET

RunStop

RUN

FUNC.

Monitor Program

NOTE: Some factory automation devices such as PLCs have alternate Run/Program modes; the device is in either one mode or the other. In the Hitachi inverter, however, Run Mode alternates with Stop Mode, and Program Mode alternates with Monitor Mode. This arrangement lets you program some values while the inverter is operating—providing flexibility for maintenance personnel.