The Comprehensive Flowmeters Resource


Absolute – This commonly  refers to a feedback device such as a resolver or an absolute encoder that provides unique position information for each discrete shaft location and  unlike an incremental feedback device which requires a known reference point an absolute feedback device retains position information when power to the system is momentarily lost

AC induction motor -class of motors that derives its name from the fact that current is induced into the rotor windings without any physical connection with the stator windings (which are directly connected to an AC power supply); adaptable to many different environments and capable of providing considerable power as well as variable speed control.

AC synchronous motor – class of motors that has its phases in correct relationship with each other at every rotor position so that the phases of the stator are synchronous with the rotor poles- adaptable to many different environments and capable of providing considerable power as well as variable speed control.

Acceleration – rate of increase in velocity with respect to time; equal to net torque divided by inertia.

Accuracy – difference between the actual value and the measured or expected value

Ambient temperature -temperature of the local surroundings

Amplifier –  an electronic device that converts low level inputs to high level outputs

Armature – rotating member of a brushed DC motor

Back emf – voltage generated when a permanent magnet motor is rotated- a limiting factor for the high speed torque output of a permanent magnet motor as it is opposite in polarity to the supplied voltage and directly proportional to motor speed

Bifilar winding – indicates two distinct windings in the same physical arrangement – these windings are usually wired together, either in series or in parallel, to form one phase

Bipolar chopper drive – drive that uses the switch mode method to control motor current and polarity

Brush – is a  conductor between the commutator and the external circuit of a brushed DC motor

Brushed DC motor – classes of motors that have  permanent magnet stators and a wound iron-core armature- as well as mechanical brushes for commutation and are capable of variable speed control however are not readily adaptable to different environments

Brushless servomotor – a class of servomotor that uses electrical feedback rather than mechanical brushes for commutation-durable and adaptable to many different environments

Case temperature rating – maximum temperature a motor case can reach without the inside of the motor exceeding its internal temperature rating

Class B insulation –  is insulation with a temperature rating of 130° C essentially the industry standard

Class H insulation – insulation with a temperature rating of 180° C

Class 220 insulation -insulation with a temperature rating of 220° C

Cogging torque – this is a measure of non-uniform velocity

Commutation – controlling the currents or voltages in the motor phases in an effort to optimize motor performance; can be achieved mechanically or electrically

Commutator – a mechanical device in a brushed Direct Current (DC) motor that passes current from the brushes to the windings

Connector – a device used for connecting cables -usually come in pairs of female and male

Continuous stall current – amount of current applied to the motor to achieve the continuous stall torque

Continuous stall torque – the maximum amount of torque a motor can provide at zero speed without exceeding its thermal capacity

Controller – used to describe collective group of electronics that control the motor 

COP Or condensed outgas product; measurement of motor cleanliness in a vacuum environment

Coupler – a device that fastens the output shaft of the motor assembly to the shaft of the load

Critically damped – describes a system where the response to an input change is achieved in the minimum possible time

Current at peak torque – the amount of current required to produce peak torque

Current sink – transistor output configured so that the load is wired from the positive side of the power source to the output and the transistor makes the circuit sink to common

Current source – transistor output configured in such a way that the load is wired from the output of the sensor to the common side of the power source so that when the transistor turns on voltage is sourced to the load

Damping ratio -ratio of actual damping to critical damping; if the damping ratio is less than one a system is said to be underdamped and if it is greater than one a system is said to be overdamped

Damping – refers to the rate of decay or settling time of a signal

Deceleration – the rate of decrease in velocity with respect to time.

Decibel – a logarithmic measure of gain equal to twenty times the log of the gain

Detent torque – torque that is present in a non-energized motor

Drive – amplifier that converts step and direction input to motor currents and voltages

Duty cycle – percentage of time the motor is on

Dynamic – refers to something that is in motion

Dynamic braking – braking that can be enacted while the motor is in motion

EMI – electromagnetic interference

Encoder – feedback device that utilizes an optical source and sensor to provide velocity and position information in the form of a digital signal; not readily adaptable to different environments-

End play – amount of axial displacement resulting from the application of a load equal to the stated maximum axial load

Excitation – external electrical energy applied to a transducer for its proper operation

Explosion proof – specification that indicates an enclosure is capable of withstanding and confining internal explosions

Feedthru – device that physically interfaces one side of a separating surface to the other 
Flowmeter –  A quantification of bulk fluid movement examples

Friction -resistance to motion due to contacting surfaces

Gear ratio – ratio of the motor input speed to the gearhead output speed

Gearhead – device that reduces motor speed and increases motor torque

Gearhead efficiency – the actual torque output divided by theoretical torque output (the torque input multiplied by the gear ratio).

Hall sensors – feedback devices used for commutation

Holding torque – maximum torque the motor can provide to hold itself in a fixed position; also called static torque

Horsepower – measurement of power .  The most common definitions equal between 735.5 and 750 watts

Hybrid step motor -class of step motors that utilizes a permanent magnet to polarize soft iron pole pieces around the rotor

Hysterisis –   the difference noted in a sensor’s output as a response to first an increasing and then a decreasing i.e.  a type of error where the system response to an increasing input signal is not equal and opposite to a decreasing input signal of equal magnitude

Idle current reduction –the  drive feature that reduces the motor current at a standstill to reduce motor heating

Incremental – this refers to an output that is measured in known increments from a known reference point

Indexer – electronics that convert high level computer or Programmable Logic Controller commands to step and direction pulses

Inductance – measurement of  the ability of a conductor to resist a change in current flow

Inertia – measurement of an object’s ability to resist a change in velocity, this property is dependent upon the mass and shape of the object

IP – European rating system for specifying equipment compatibility with dust, water, and shock; also recognized in the U.S. IP standads for Ingress Protection

Lamination – material that holds the soft iron pole pieces and permanent magnet around the rotor

Linear actuator -refers to an assembly that transfers the rotary motion of a motor to linear motion

Magnetic stack -one set of soft iron pole pieces and permanent magnet; step motors typically have one, two, and three magnetic stack versions for each frame size

Microstepping – this is  a method of proportioning current so that the full steps of the step motor are broken into smaller – microsteps

Motor efficiency – mechanical power output of the motor divided by electrical power input to the motor

MTBF -the average time between failure – a measurement of reliability.

NFPA – (USA )National Fire Protection Association responsible for providing safety information 

NFPA 496 – a guideline published by the NFPA that among other things describes the application of positive pressure with dry air or nitrogen to convert the interior of a motor to a non-hazardous area

Oil-filled – describes an enclosure  that has been filled with oil to prevent leakage

Open-loop -describes a system that operates without feedback.

Opto-isolation – a method of sending a signal from one piece of equipment to another without the usual requirement of common ground potentials.

Outgassing – evaporation of oil – dirt – or any other substance from a surface after it is placed in a low pressure or vacuum environment

Parallel – refers to a motor winding configuration – motors that are wired in parallel produce more torque at high speeds but less torque at low speeds than motors wired in series

Peak torque – the maximum torque that can be delivered for even a short period of time

Permanent magnet motor – general class of motors that uses permanent magnets to produce torque

Phase – describes one or more signals that neither lag nor lead one another; step motors typically have two phases and brushless motors typically have three phases

Phase angle – angle at which the steady state input signal leads the output signal

PMDC motor – permanent magnet DC motor; also called a brushed DC motor

Power – the rate at which work is done and this is equivalent to torque times rotational speed or voltage times current

Pressure compensator – device that equalizes the internal pressure of the motor with the external pressure of the environment

Pulse rate – frequency of pulses applied to the drive

Pulse Width Modulated (PWM) drive – drive that utilizes a method of switching voltage on and off at fixed but variable frequencies

Purged and Pressurized: NFPA 496 describes the application of positive air or dry nitrogen to purge and then pressurize an enclosure for hazardous area duty. The positive pressure in the enclosure inside the enclosure does not allow for ignitable gases to penetrate into the enclosure.

Rated current – maximum allowable current a motor can receive without exceeding its thermal limit

Rated torque –  torque producing capacity at a specified speed

Reflected load inertia – this refers to the load inertia as seen by the motor – e.g., a gearhead reduces the inertia of the load as seen by the motor by a factor of the gear ratio squared

Regeneration – refers to the electrical energy returned to the drive when a motor acts like a generator as it is slowed mechanically

Regulator (Traction Engine) This controls the amount of steam allowed into the cylinder
And so  the speed of the engine. It is operated by a lever at the drivers position

Resolver-to-digital converter – those electronics that convert an analog resolver signal to a digital – encoder-like signal

Resolvers – rugged electromagnetic feedback devices that act like a rotating transformer to provide an analog signal with velocity and position information- adaptable to many different environments because of its construction

Resonance –   oscillatory behavior usually regarded as unfavourable (for instance e.g slow single step response and settling times) caused by mechanical limitations

RMS – the root mean square and is derived from the  power dissipation / AC current.

Rotor – the  rotating member of a motor.

Series –  refers to a motor winding configuration- motors that are wired in series produce more torque at low speeds but less torque at high speeds than motors wired in parallel

Servomotor -class of motors that operates within a closed-loop system with respect to both position and velocity

Settling time –  time required for the motor to come to rest at its commanded position; a measure of system performance

Single step response time – the time required for the motor to rotate one step and settle at that position – this can be a measure of a system performance

Stall torque – the amount of torque developed with voltage applied and shaft locked

Stator – stationary member of a motor

Step angle – angular distance of a single full step

Step motor – class of motors that provides incremental motion, or steps, in response to pulses of current that alternately change the polarity of the stator poles; step motors do not require feedback

Stiffness– relationship describing motor displacement from a fixed position due to an applied torque of specified value

TAD is the  total accumulated dosage

TEFC – totally enclosed, fan cooled meaning that the motor is equipped for fan cooling by means integral to the motor but external to the enclosing parts.

TENV –  totally enclosed, non-ventilated meaning that the motor is not equipped for cooling by means external to the enclosing parts

Thermal current – see rated current.

Thermal cycling – refers to the expansion and contraction of a material that is heated and cooled repeatedly over time

Thermal resistance – temperature rise per unit of power loss

Torque – force that tends to rotate a body

Torque constant – relationship of torque output per ampere

Torque to inertia ratio – measurement of the motor’s maximum ( no load) acceleration

Torr – unit of measurement equal to 1 mm of Hg- commonly used when specifying vacuum pressure levels

Transducer – device that produces an electrical output that is proportional to a mechanical input . Various types exist for different purposes.

TTL – transistor transistor logic.

Tuning – adjusting the parameters of a system in an effort to optimize performance.

Type C Face – face mounting with a male pilot  fitted with threaded holes in the mounting surface

Unipolar drive -drive that is capable of driving phase current in only one direction

Vacuum – refers to a volume of space that has little or no pressure due to the absence of air or any other gasses; there are differing degrees of vacuum
Variable reluctance motor – class of motors whose rotor has neither permanent magnets nor electrical windings – capable of high speeds, but produces little torque.

Velocity – change in position with respect to time; velocity has both a magnitude and a direction.

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