Method and apparatus for testing DC motors

A method for testing a DC motor, said method comprising the steps of:

• applying a constant voltage across the terminals of said DC motor for a first predetermined time interval;
• sensing the current flow through said DC motor during at least a portion of said first predetermined time interval;
• with an electrical circuit, generating a first electrical signal if the current flow through said DC motor falls below a predetermined level during said portion of said first time interval;
• causing a constant current to flow through said DC motor for a second predetermined time interval;
• sensing the voltage across the terminals of said DC motor during at least a portion of said second predetermined time interval;
• and
• with an electrical circuit, generating a second electrical signal if the terminal voltage of said DC motor is outside a predetermined voltage range at the end of said portion of said second predetermined time interval;
• whereby, the occurrence of either of said first or second electrical signals may be used to indicate a defect in said DC motor.

Apparatus for testing a DC motor which comprises:

• a constant voltage source of DC electrical energy;
• a constant current source of DC electrical energy;
• first circuit means for connecting said constant voltage source to said DC motor for a first predetermined time interval;
• second circuit means for sensing the magnitude of current flow through said DC motor when it is connected to said constant voltage source and for generating a first electrical signal if said current magnitude falls below a predetermined level during at least a portion of said first predetermined time interval, said second circuit means comprising a current shunt for generating a voltage signal proportional to the current flow through said DC motor, and an amplifier circuit having an input coupled to said current shunt, a gate circuit having an input coupled to the output of said amplifier circuit, and a memory device having a controlled electrode coupled to the output of said gate circuit, said first electrical signal being an electrical state of said memory device which state occurs if the magnitude of said current through said shunt falls below said predetermined level during said portion of said first predetermined time interval;
• third circuit means for connecting said constant current source to said DC motor to cause a constant current to flow through said DC motor for a second predetermined time interval;
• and
• fourth circuit means for sensing the voltage across the terminals of said DC motor during at least a portion of said second predetermined time interval and for generating a second electrical signal if said terminal voltage is outside a predetermined voltage range at the end of said portion of said second predetermined time interval;
• the presence of either of said first or second electrical signals being indicative of a defect in said motor.

Apparatus for testing a DC motor which comprises:

• a constant voltage source of DC electrical energy;
• a constant current source of DC electrical energy;
• first circuit means for connecting said constant voltage source to said DC motor for a first predetermined time interval;
• second circuit means for sensing the magnitude of current flow through said DC motor when it is connected to said constant voltage source and for generating a first electrical signal if said current magnitude falls below a predetermined level during at least a portion of said first predetermined time interval;
• third circuit means for connecting said constant current source to said DC motor to cause a constant current to flow through said DC motor for a second predetermined time interval;
• and
• fourth circuit means for sensing the voltage across the terminals of said DC motor during at least a portion of said second predetermined time interval and for generating a second electrical signal if said terminal voltage is outside a predetermined voltage range at the end of said portion of said second predetermined time interval, said fourth circuit means comprising an amplifier circuit having an input coupled to the terminals of said DC motor and to a reference voltage level, said amplifier producing an output signal which initiates said second predetermined time interval, a low motor-terminal-voltage detection circuit, a high motor-terminal-voltage detection circuit, a gate circuit coupled to said low and high motor-terminal-voltage detection circuits, a memory device, and means for enabling, at the end of said second predetermined time interval, said memory device to obtain an electrical state indicative of a defect in said DC motor if, at the end of said second predetermined time interval, said low motor-terminal-voltage detection circuit senses a motor-terminal-voltage below a first predetermined level, or if said high motor-terminal-voltage detection circuit senses a motor-terminal-voltage above a second predetermined level;
• the presence of either said first or second electrical signals being indicative of a defect in said motor.