Tachometer: A small generator normally used as a speed sensing device.
Tachometer Generator (Tach): A generator, mechanically coupled to a rotating machine whose function is to generate a voltage, the magnitude or frequency of which is used either to determine the speed of rotation of the common shaft or to supply a signal to a control circuit to provide speed regulation.
Temperature Codes: In explosion-proof motors, the temperature code is assigned by the National Electrical Code (NEC) to group together flammable liquids, vapors, dusts, and flyings into groups with similar flashpoints.
Temperature, Ignition: In explosionproof motors, the temperature at which once attained will cause an explosion to occur in the volatile environment.
Temperature Rise: The measurable rise above the ambient temperature at which the fully loaded motor operates. This temperature rise is the result of the heat losses in the stator winding, core, and rotor.
Temperature, Ultimate: The highest temperature of any spot to which a specific class of insulating materials can be continuously subjected without marked decrease in the system’s designed life.
Terminal Blocks or Strips: An accessory available to titan frame motors which fits into the conduit box and provides a means to group terminating leads from accessories separately from the main leads.
Test - Complete Initial: A motor test which consists of full load heat run, percent slip, no load current, full load current, locked rotor current, locked rotor torque, breakdown torque (calculated), efficiency and power factor at 100%, 75% and 50% full load, winding resistance, high potential, and bearing inspection. Complete initial tests are per IEEE 112 Method B and performed on a dyno.
Test - Noise: A motor test of the sound levels produced by the motor at certain distances. All sound tests are performed at no load in a free field. Noise tests are per IEEE 85.
Test - Short Commercial: Motor test conforming to NEMA MG1-12.51, consisting of no load current, locked rotor current, winding resistance, high potential, and bearing inspection.
Test - Spray: A test of the motor stator on sealed, formwound stators only. The stator is sprayed with water and then measured for seepage in the winding.
Test - Vibration: A test of the motor when operating to ensure the vibration does not exceed certain levels.
Thermal Overload Relay: A thermal overload relay functions (trips) by means of a thermally responsive system.
Thermal Protector: A protective device for assembly as an integral part of the machine and which, when properly applied, protects the machine against dangerous overheating due to overload and, in a motor, failure to start. Notes: 1) It may consist of one or more temperature sensing elements integral with the machine and a control device external to the machine; 2) When a thermal protector is designed to perform its function by opening the circuit to the machine and then automatically closing the circuit after the machine cools to a satisfactory operating temperature, it is an automatic reset thermal protector; 3) When a thermal protector is designed to perform its function by opening the circuit to the machine but must be reset manually to close the circuit, it is a manual reset thermal protector.
Thermal Protector, Winding - Therma-Sentry: A USEM complete thermal protection system for windings, protecting the motor from running overloads. It will also protect the motor from abnormally high ambient temperatures, voltage unbalance, high or low voltage, ventilation failure and single phasing. It consists of three thermistors, solid state control for mounting in the customer supplied panel, with 3 amps control circuit capacity.
Thermal Protector, Winding - Thermistors: A non-linear resistance temperature detector made from semi-conductor material. There are two general types, positive temperature coefficient (PTC) which has a resistance that increases with increasing temperature, and negative temperature coefficient (NTC) that has a resistance that decreases with increasing temperature. USEM’s standard is PTC. Lines should not exceed 50 ohms.
Thermal Protector, Winding - Thermocouples: A pair of two dissimilar materials which generates a minute voltage in proportion to its temperature. Such devices may be used as a signal source in indicating instruments and control equipment.
Thermal Protector, Winding - Thermostats: Snap action, bi-metallic, temperature actuate switches installed in the connection end-turns of the motor winding. Their purpose is to activate a warning device or shutdown the motor upon excessive winding temperatures.
Thermal Protector, Winding - Winding RTD's: Precision, wire-wound resistors with a known temperature-resistance characteristic. Recognized for their accuracy, the RTDs resistance increases with temperature rise in a known and highly repeatable manner. 2 RTDs per phase/6 per motor are USEM’s standard offering.
Thermistor: A non-linear resistance temperature detector made from semi-conductor material. The thermistor trip point is defined as the point where resistance suddenly rises or falls depending on the type of thermistor. It is usually used with a solid state controller that monitors the thermistor resistance and performs a preprogrammed f unction at the thermistor trip point. Thermistors are available with a multitude of preset non-adjustable trip points. This type of temperature detection device is used in the USEM THERMASENTRY motor protection device.
Thermocouple: A junction of two dissimilar materials which generates a minute voltage in proportion to its temperature. Such devices may be used as a signal source in indicating instruments and control equipment.
Thread Speed: A fixed low speed, usually adjustable, supplied to provide a convenient method for loading and threading machines. May also be called a preset speed.
Thrust: In vertical motors an unusually heavy weight or load in one or both directions.
Thrust Bearing: A specialized bearing design to handle heavy weights or loads in one or both directions.
Thyristor: A three junction semiconductor device that can be switched from the off state to the on state or vice versa.
Time Delay: A time interval that is purposely introduced in the performance of a function.
Torque: A turning force applied to a shaft, tending to cause rotation. Torque is normally measure in pound/feet and is equal to the force applied times the radius through which it acts.
Torque, Breakdown: The maximum torque the motor will develop with rated voltage applied at rated frequency without an abrupt drop in speed. Usually expressed as a percentage of full-load torque.
Torque, Constant: An application which requires the same torque at all operating speeds. Horsepower varies directly with the speed. Examples of constant torque applications include conveyors, hoists, and positive displacement pumps.
Torque Control: Motor torque is regulated instead of motor speed.
Torque, Full-Load: The torque necessary to produce its rated horsepower at full-load speed.
Torque, Locked-Rotor: The torque the motor will develop at rest (for all angular positions of the rotor) with rated voltage and frequency applied.
Torque, Pull-Up: The minimum torque developed during the period of acceleration from locked-rotor to the speed at which breakdown torque occurs. For motors which do not have a definite breakdown torque (NEMA design D), pull-up torque is the minimum torque developed up to the rated full-load speed. Usually expressed as percentage of full-load torque.
Torque, Variable: An application in which the torque required varies as the square of its speed. Horsepower requirements increase as the cube of the speed. Examples include: centrifugal pumps and blowers, turbine pumps, and fans.
Totally Enclosed Machine (Motor): A totally enclosed machine is one so enclosed as to prevent the free exchange of air between the inside and the outside of the case, but not sufficiently enclosed to be termed airtight.
Transducer: A device that converts one energy form to another (e.g., mechanical to electrical). Also, a device that when actuated by signals from one or more systems or media, can supply related signals to one or more other systems or media.
Transient: A momentary deviation in an electrical or mechanical system.
Translator: A solid state, three terminal device that allows amplification of signals and can be used for switching and control. The three terminals are called the emitter, base and collector.
Trigger Circuit: The circuit used to gate a thyristor that causes it to conduct current.
Turn: A complete encirclement of the slots into which the coil is placed.
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