Main Body

### TORQUE DEFINITIONS

### VELOCITY DEFINITIONS

### CURRENT DEFINTIONS

### TEMPERATURE DEFINITIONS

### TIME CONSTANT DEFINITIONS

### WINDING DEFINITIONS

### POWER DEFINITIONS

### MECHANICAL CHARACTERISTICS DEFINITIONS

## GLOSSARY |

**Cogging torque (Tcog)**

Cyclic torque in an un-energized motor resulting from the tendency of the rotor and stator to align themselves in a position of minimum magnetic reluctance

**Continuous stall torque (Tcs**

Maximum continuous output torque that the motor can develop under a stall condition without the motor exceeding its rated temperature

**Peak torque (Tp)**

Maximum torque developed by a motor under specified conditions when the maximum allowable peak current is applied.

**Rated torque (Tr)**

Continuous torque

Full load torque

Output torque

Torque developed at rated voltage and rated speed without exceeding the temperature rating.

**Torque ripple**

Variation of torque within one shaft revolution under specified test conditions, expressed as the ratio of peak-to-peak torque amplitude to average torque (not including cogging torque)

**Viscous torque**

Dynamic friction torque

The resistance to motion that is velocity dependent

**Torque constant (KT)**

The ratio of change in torque to change in current developed by a motor.

Torque constant is temperature dependent and can be mathematically derived from the back EMF constant.

(KE). For SI (metric) units, KT = KE. For English units, the following conversions apply:

a) KT = KE /11.834 for brush commutated or trapezoidal EMF brushless motors;

b) KT = KE /13.017 for sinusoidal EMF brushless motors with square wave current;

c) KT = KE /13.662 for sinusoidal EMF brushless motors with sinusoidal current.

The available shaft output torque is the developed torque reduced by frictional and rotational losses.

**NOTE In industry, velocity is commonly referred to as speed and is expressed in rpm.**

**No load speed (?nl)**

Actual motor speed with no external load and specified terminal voltage

**Rated speed (?r)**

Continuous speed

Maximum motor speed that can be achieved while maintaining a specified rated torque.

**Maximum mechanical speed (?max)**

Highest speed at which the shaft can be rotated without mechanical damage

**No-load current (Inl)**

The current drawn by an unloaded motor at the rated voltage

**Continuous current (Ic.)**

Current required to develop rated torque without exceeding the temperature rating.

**Continuous stall current (Ics.)**

Maximum current that can be continuously applied to a stalled motor without exceeding the temperature rating of the motor.

**Peak current (Ip.)**

acceleration current

Maximum intermittent current that does not cause motor damage or irreversible degradation of motor performance.

**Rated current (Ir.)**

Current developed at rated voltage and rated speed without exceeding the temperature rating.

**Demagnetization current (Idm.)**

The winding current that creates a magnetic flux opposing the main field flux which irreversibly decreases the field strength of the motor magnets.

**Ambient temperature (Tamb)**

Temperature of the cooling medium, usually air, immediately surrounding the device.

**Case temperature (Tcase)**

Temperature of the surface of a device.

**Maximum allowable winding temperature (Tmax)**

Maximum temperature of the winding permitted by the temperature class of the insulation system used.

**Temperature rise (?T)**

Increase in temperature (in oC) of a device above ambient temperature at designated conditions.

**Electrical time constant (?e)**

Time required for the current to reach 63.2% of its steady state value when a step input voltage is
applied.

**Mechanical time constant (?m)**

Time required for a device to reach 63.2% of its steady state velocity after a zero source impedance step voltage input is applied.

**Thermal time constant (?th)**

Time required for a device to reach 63.2% of steady state temperature rise with constant power dissipation.

**Back EMF**

**Counter EMF (Eg)**

Internally generated voltage produced by the relative movement between the magnetic field and the armature winding when measured on an open circuit.

**Back EMF constant (Ke)**

Amplitude of the counter EMF waveform generated at the motor terminals as it is moved through the magnetic field at a constant velocity divided by that velocity:

**Motor terminal inductance (La)**

Inductance of the armature as measured across the terminals of the device.

**Motor terminal resistance (Rm)**

Resistance of the armature winding and, where applicable, of the connections measured at the brush contact points.

**Rated power (Pr)**

The ability of a motor to output its full power for a sustained period of time

*NOTE Power is calculated by the formula*

Pr = Tr x ?r

where

?r is the rated speed, Tr is the rated torque

**Duty cycle**

Relation between the on time and the off time of a device.

**Efficiency (h)**

Ratio of power output to power input of a machine, expressed as a percentage.

**Safe operating area**

Area defined by speed and torque conditions at which the motor will operate within its thermal
limitations.

**Moment of inertia (Jm)**

Property of matter that causes the mass to resist any change in its motion.

**Breakaway torque (Tbr)**

Starting torque

Static friction torque

Mechanical resistance that a device must overcome before motion can occur.

**Friction torque (Tf)**

Resistance to motion that is independent of velocity.

**Torsional resonance**

Rotational oscillation that occurs in any rotating system when it is being excited at or near its natural frequency.

**Locked rotor**

Stalled motor

Condition where the rotor is held stationary while power is applied to the motor terminals.