A printing press requires a supply of oil at a constant pressure. Therefore the oil is supplied by a pump which can vary its speed. The oil supply pressure in the machine is measured by a pressure gauge. The pressure gauge sends a signal to a computer. The computer compares the actual pressure to the desired setpoint pressure. The computer then sends a small current through a wire to the motor drive. This control current varies from 4 to 20 milliamps depending on the desired motor speed. The motor drive has a power supply input of 240 volts. It adjusts the output voltage to the motor depending on the input current from the computer. As the voltage to the motor changes, the speed of the pump changes.
The desired supply pressure is 20 psig. One day the oil supply gauge is reading only 12 psig. You check the motor, and it is running very slowly. You suspect that the problem may be in the motor drive.
How can you check to see if the motor controller is causing the problem?
A)Measure the current between the computer and the drive.
B)Disconnect the pressure gauge and see what happens.
C)Measure the speed of the pump motor.
D)Measure the actual input voltage of the 240V supply power.