Glossary of Terms

Pull-out torque – The maximum torque which a synchronous or stepper motor can produce and still maintain synchronous speed at designated voltage and frequency. Tested by progressively loading motor until motor falls out of synchrony. (Variable)

Stall Torque – The maximum torque that can be applied to a non-synchronous motor (eg. DC motor, hysteresis motor, induction motor output shaft without stopping rotation at designated voltage and frequency.  Tested by progressively loading motor until the output shaft of the motor stops rotating. (Variable)

Pull-in Torque – The maximum constant torque which a synchronous or stepper motor will accelerate to synchronous speed at designated voltage and frequency. Tested while under power, after loading motor to pull-out, reducing load until motor returns to synchrony. Motor remains under power throughout the test. (Variable)

Starting Torque – The maximum amount of torque against which a synchronous or stepper motor can start and run at synchronous speed at designated voltage and frequency. Tested by pre-loading the output shaft in the opposite direction of rotation with a given load, applying designated voltage and frequency, and observing when the motor starts.. Use torque gage or hysteresis brake to create load. (Variable)

Static Torque – A specified torque load applied to the output shaft of a non-energized gear motor at which it must survive without damage. Tested by applying a torque load in the opposite direction of rotation, without power applied. (Attribute)

Operating Torque / Running Torque / Run Torque – The specified minimum torque required by a customer’s application at designated voltage and frequency. (Variable)

Guidelines and Notes

If the pull-out torque specification exceeds the static torque specification of the motor, motor damage could occur due to testing. Engineering should be consulted prior to measuring pull-out torque if the blueprint does not annotate specific test instructions. If the motor pull-out torque is measured and exceeds the static torque specifications, it is to be considered a destructive test; the motor is no longer fit for use and is to be scrapped.

Engineers should be careful not to confuse the definitions with test parameters and instructions. Inspectors will collect variable data wherever possible, unless instructed otherwise, potentially damaging the motor in some cases. For example, Pull-out torque 240 oz.-in. min. Inspector applies the load until motor falls out of synchronous speed at 620 oz.-in. This causes motor damage. To avoid this, “Pull-out Torque 240 oz-in min. (Attribute Only)” is noted on the drawing, telling the inspector to measure the item as a pass-fail characteristic.