Every effort is made to include terms which the author believes are relevant. The definitions are intended to provide a descriptive definition without resorting to extensive theory and formulas.
Accuracy – The degree of uncertainty with which a measured value agrees with the ideal values. Accuracy class of instrument transformers are defined by the requirements of:
- ANSI C57.13 Standard metering accuracy classes are 0.3, 0.6 and 1.2.
- IEC 60044-1 Standard metering accuracy classes are 0.2, 0.5 and 1.0.
Active Power – The RMS voltage multiplied by the RMS current of the fundamental multiplied by the cosine of the phase angle between the current and voltage.
Ambient Temperature – Temperature of the surrounding air.
Amorphous Core – A type of transformer core material which offers high permeability, minimizing “no load” transformer power losses. At the molecular level the material is in a non-crystalline formation. This formation is achieved by quickly cooling the molten metal, solidifying the metal before it has a chance to form a crystalline structure.
Apparent Power – The product of the applied voltage and current in AC circuit. Apparent power, or volt-amps, is not the true power of the circuit since power factor is not considered in the calculation.
Auto Transformer – A transformer used to step voltage up or down. The primary and secondary share a single winding, therefore the primary and secondary are not isolated.
Auxiliary Power – A power source, other than that producing the measured input quantity, which supplies the power necessary for the correct operation of the transducer.
Average Responding – The measurement of an AC voltage or current obtained using a DC instrument with a rectifying input circuit that converts AC energy to DC. The meter scale or readout is usually calibrated in terms of the corresponding RMS values, but is accurate only for pure sine wave inputs.
Bifilar coil – Two wires wound side by side in parallel windings to form equivalent and symetrical coils.
Bar – A unit of measure of pressure. Typically used when describing weather conditions (one atmospheric pressure is equal to 1.01325 bar). The unit of measure conversion is; 1 bar = 100 kPa (Pascal) = 14.5037744 PSI.
BIL – Basic Insulation Level
Bimetallic – See Temperature Measurement Device, Bimetallic
BLOG – A BLOG (weB LOG) is a WEB based diary which covers any subject the author(s) desires to cover. A BLOG can have one to many authors, each contributing entries. Subjects range from war zone correspondence, to arts & crafts topics, to family correspondence.
Burden – In a current or potential transformer, the burden in VA is the maximum load the transformer can support while operating within its accuracy rating.
Calibration – Adjustment of a instrument so the output is always within a specified range for particular values of the input.
CAT Rating Rating of the instrument for voltage level of usage, insulation and surge withstand;
- CAT II – Measurement of low voltage applications, such as household appliances.
- CAT III – Measurement of building level applications, such as breaker panel.
- CAT IV – Measurement of electric utility level applications.
Closed-Loop Hall Effect Sensor – A current sensor based upon the Hall Effect principle that a magnetic field (primary conductor) applied perpendicular to an electric current will create a proportional Hall voltage perpendicular to the two fields. The closed-loop design incorporates a secondary winding which is used to offset the magnetic field of the primary conductor providing an instantaneous representation of the primary current.
Creepage – A measurement of the length of a short circuit conductive path that may occur across an insulated surface.
Crest factor – A measurement of the ratio between the peak value of a sinusoidal wave form and the effective value. As an example, a DC wave form has a Cress factor of 1. For alternating AC currents, the peak value may be compared to the RMS value of the waveform.
Current Transformer – An instrument transformer used to accurately scale ac currents up or down and/or to provide isolation. Generally used to scale large primary or bus currents to usable values for measuring (or control) purposes. The current measurement range is expressed as the ratio of full scale primary current to full scale secondary current. The primary winding is connected in series with the conductor carrying the current to be measured or controlled. There are two classifications of current transformers. Single Loop Primary type and Wound Primary type. In Single Loop type current transformers the primary winding is provided by the line conductor and is not an integral part of the transformer. In Wound Primary type the primary winding is an integral part of the transformers and usually consist of more that one turn. Wound Primary transformers are used in applications that require very high accuracies, as the position of the primary winding relative to the core magnetic field is fixed.
Current Ratio – Commonly used when specifying a current transformer. It is the relationship between the primary input value and by the secondary output value. For example: a current transformer that has a primary input value of 250 Amperes and a secondary output value of 35 ma will have a Current Ratio of 250:0.035.
Delay on Energization – A term describing a mode of operation relative to timing devices. Delay begins when the initiate switch is closed, or upon application of power to the input. Same as Delay on Make.
Delay on Make – Same as delay on energization.
Dielectric Strength – The continuous voltage a material can withstand without deteriorating/ breaking down.
Duty Cycle – The amount of time that a particular device is operating or on … expressed as time or percentage.
Effective Power – In AC measurements, effective power (measured in watts) equals the product of voltage, current and power factor (the cosine of the phase angle between the current and the voltage).
Ferroresonance Transformer – A ferroresonance transformer is a constant voltage transformer or voltage regulator. The transformer is designed to operate in the region of magnetic saturation. When the magnetic core is in saturation large fluctions in primary winding current will result in minimal fluctuation in magnetic flux and secondary output. The addition of a LC (inductor – capacitor) circuit tuned to the AC frequency filters out any harmonic distortions.
Frequency Shift Keying (FSK) – Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier wave. The simplest FSK is binary FSK (BFSK). As suggested by the name, BFSK uses two discrete frequencies to transmit binary (0’s and 1’s) information. With this scheme, the “1” is called the mark frequency and the “0” is called the space frequency.
Full Scale (F.S.) – The specified maximum value of the input quantity being measured that can be applied to a device without causing a change in performance beyond the specified tolerance.
Full Scale Output – The specified maximum output value for which the stated accuracy condition applies.
GIS – Gas Insulation Switch – Typically kV rated switches incorporated into electric power distribution networks that utilize SF6 (sulfur hexafluoride) gas internally as the insulating media.
GOSS – Grain Oriented Silicon Steel
Hall Effect – The Hall-effect is based upon the principle that a magnetic field applied perpendicular to a current will create a proportional Hall voltage perpendicular to the two fields. This technology allows; contactless sensing (sensing either an external magnet or a ferrous object) and non-intrusive current sensing. Hall-effect sensors are used for highly accurate gear-tooth sensing, direction detection, linear sensing, speed sensing, position sensing and contactless switching.
HART® Protocol – The HART protocol uses Frequency Shift Keying (FSK) on the Bell 202 1200 baud data communication standard to superimpose digital information on a conventional two wire 4 to 20mA analog signal. This enables two way communications between the host (master) device and the field instrumentation without interfering with the underlying analog signal. The HART protocol has become widely used in the process control industry. The protocol is maintained by an independent organization, the HART Communication Foundation.
Hertz (HZ) – Unit of measure for frequency. Equal to cycles per second.
Hysterisis – An error resulting from the inability of an electrical signal or mechanical system to produce identical readings or position when approached slowly from either direction. Also referred to as deadband.
IEC 60044-1 – International Electrotechnical Commission “Instrument Transformers – Part 1: Current Transformers” standard. This standard covers the requirements and tests necessary for current transformers for use with electrical measuring instruments and electrical protective relays. The standard is applicable for electrical measuring instruments and electrical protective relays at frequencies from 15HZ to 100HZ.
IMAP – Internet Message Access Protocol. This protocol is used to retrieve email from an email server and underlies the email application used by the email client (USER). This protocol retrieves emails, removing the email from the server only upon a specific command. This feature is useful when the email server is access through multiple devices/ paths/ locations (e.g. email application in the office, through the web, through a mobile phone, …). An alternative email protocol is POP … please see POP.
Impedance – The opposition in an electrical circuit to the flow of alternating (AC) current. Impedance consists of ohmic resistance (R), inductive reactance (L), and capacitive reactance (C).
Inrush – The initial surge of current through a load when power is first applied. Lamp loads, induction motors, solenoids, contactors, valves, and capacitive loads all have inrush currents higher than the normal running or steady state currents. Resistive loads, such as heater elements, do not exhibit inrush.
Instrument Transformer – A transformer which is intended to reproduce in its secondary circuit, in a definite and known proportion, the current or voltage of its primary circuit with the phase relations substantially preserved.
IP Code (International Protection Rating) – The IP code is defined by the international standard IEC 60529. The IP is followed by a two(2) digit number with an optional letter. The code classifies the degree of protection offered by the product against intrusion from solid and liquid objects. Reference http://en.wikipedia.org/wiki/IP_Code.
Isolation – To be electrically separate. A measure of the strength of the dielectric providing the electrical isolation or separation.
Linearity – A measure of the departure from a straight-line response in the relationship between the primary and secondary quantities, where the change in one is directly proportional to a change in the other. Normally expressed as a maximum percentage
Loop Powered – The transducer uses the power supplied by the primary current measuring loop to power the transducer. An auxiliary power supply is not required.
Loop Resistance – The electrical resistance, in ohms, of a complete transducer circuit exclusive of an instrument’s internal resistance.
m H2O – The amount of pressure exerted by a column of water 1 meter high. Commonly used as the unit of measure for liquid level sensors and depth sensors.
Magnetic Permeability – The degree of magnetization of a material that responds linearly to an applied magnetic field . (Wikipedia)
Magnetic Saturation – Magnetic saturation is the state when the material cannot absorb a stronger magnetic field, such that an increase of magnetization force produces no significant change in magnetic flux density in the material. (Wikipedia)
MOV – Metal Oxide Varistor is an electrical component used to protect electrical circuits against voltage surges. The MOV is connected between the line voltage and ground. As long as the line voltage is at normal levels, the MOV is a high resistance path to ground. If the line voltage exceeds the designed threshold, the resistance decreases providing a path to ground effectively clamping the line voltage. The common household appliance that incorporates MOVs is the surge protected AC power strip.
Mutual Inductance – Mutual inductance is where the changing magnetic field of one circuit induces a changing voltage and/ or current in a second circuit. Current or voltage transformers are based upon the principle of mutual inductance. The rate of change of the current in the primary and the turns ratio of the primary to secondary determine the voltage and/ or current relationship between the primary and secondary (V or A secondary = mutual inductance factor * dA/ dt primary).
Nanocrystalline Magnetic Material – Iron based alloy magnetic core material which is treated to create a mixture of amorphous and crystalline structures in the material.
Non-Linearity – In an ideal system, the input-output relationship between variables is linear(i.e. straight line) Any departure from straight line is expressed as non-linearity.
Open-Loop Hall Effect Sensor – A current sensor based upon the Hall Effect principle that a magnetic field (primary conductor) applied perpendicular to an electric current will create a proportional Hall voltage perpendicular to the two fields.
Operating Voltage – A nominal operating voltage with a specified tolerance applied. The design voltage range to remain within the unit’s operating tolerances.
OR-ing Diodes – Refers to diodes used in power supply designs where the power supplies are designed to operate in a parallel/ redundant application. The diodes are incorporated into the output(s) of the power supply. In case of a power supply failure, these diodes prevent the good power supply from attempting to source power to the failed power supply through its outputs.
Pa, kPa, mPa – “Pa” or Pascal is a unit of measure used in the measurement of pressure. A Pascal is one(1) Newton per square meter, where a Newton is the amount of force necessary to accelerate 1 kilogram to one(1) meter per second per second. kPA is 1000 Pascals and mPa is 1,000,000 Pascals. One(1) Psi (pounds per square inch) is equal to 6.896 kPa.
PC Alloy – A blend of polycarbonate with an engineered plastic that offers good chemical resistance, impact resistance, and heat resistance. Widely used in electrical and electronics devices subject to rough handling and harsh ambient operating environments.
Permeability – A measure of the ability of a material to support the formation of a magnetic field.
Permalloy – The trademark for any of several alloys of iron (FE) and nickel (NI) having high magnetic permeability, low coercive force, low hysteresis loss magnetic properties . This material is used in the fabrication of high performance transformer cores.
Phase Angle – The difference by which an alternating signal lags or leads another signal, typically expressed as degrees. Phase angle may be a measure of power factor when used to indicate the relationship of a voltage to current signal for a non-resistive load. Phase angle may also be used to measure the different in phase between the primary and secondary of a current or voltage transformer.
Pollution Degree Rating for Electric Equipment – The pollution degree is a classification of the amount of pollution and condensation in the operating environment. The classification reflects the possibility of pollution and condensation providing a hazardous conductive short circuit path.
- Pollution Degree 1 – Operating environments are either non-condensing or no pollution exists.
- Pollution Degree 2 – Operating environments are either non-condensing or non-conducting pollution exists.
- Pollution Degree 3 – Harsh industrial operating environments with conducting pollution or pollution which conducts with condensation.
- Pollution Degree 4 – Outdoor environments subject to conducting elements such as rain, snow …
Polyphase Wattmeter – A wattmeter consisting of 2 or 3 single phase watt meters mounted in the same package. The watt sensing elements can be electronic transducers. A dual element wattmeter will measure power in a 3 phase system regardless of power factor, voltage or current variations between phases. Most common types are 2,2« or 3 element forms. In 4 wire circuits, with the 4th wire carrying current, the 2« or 3 element type is used. If there is voltage imbalance, only the 3 element units can be employed.
POP – Post Office Protocol. This protocol is used to retrieve email from an email server and underlies the email application used by the email client (USER). This protocol retrieves and removes the email from the server. An alternative email protocol is IMAP … please see IMAP
Power – A source or means of supplying energy. The unit of measurement is the watt. 1 Horsepower is equal to 745.7 Watts.
Power Factor – The RMS current of the fundamental harmonic divided by the Total RMS current multiplied by cosine (where is the phase angle between the current and voltage. A Power Factor of 1 implies all of the electrical energy is available as Active Power, a power factor of less than 1 implies losses due to Reactive Power.
Proof Pressure – The specified maximum pressure that can be applied to a sensor without causing permanent damage.
PTC – Positive Temperature Coefficient. A PTC device uses a unique polymer based material to protect electrical circuits against over current conditions. In normal operation, the PTC device offers minimal resistance. In an over current condition, the temperature of the polymer material rises. As the temperature rises, the PTC device limits the flow of current. As the flow of current returns to normal, the PTC device cools down and returns to its former resistance level.
Pulse Width Modulation (PWM) – Adjustment of the duty cycle of a signal or power source, to either convey information over a communications channel or control the amount of power sent to a load. http://en.wikipedia.org/wiki/Pulse_width_modulation
Range – Nominal operating limits, specified by the lowest calibration point to the highest calibration point.
Rated Continuous Thermal Current Factor (RF) – The multiple of the rated primary current of a current transformer that is the maximum continuous primary current that can be maintained without exceeding the limiting temperature rise from 30° C average ambient air temperature.
Rated Output – The maximum output of a device at standard calibration
Ratios – The relationship between the primary input value divided by the secondary output value. For example: a current transformer that has a primary input value of 600 Amperes and a secondary value of 5 Amperes will have a Current Ratio of 600:5 and a Turns Ratio of 120:1. It is important to use the term Current Ratio for most applications because it defines the current handling capacity of wire used in the secondary winding. The Turns Ratio only refers to the winding ratio and does not define the current handling capacity of the either primary or secondary windings.
Real Power – Same as Effective Power.
Reactive Power – A component of apparent power (volt-amps/ VAR) which does not produce any real power (watt) transfer
Remanence or Remanence magnetization or residual magnetization – The magnetization left behind in a ferromagnetic material after an external magnetic field is removed. When a magnet is “magnetized” it has remanence.
Repeat Accuracy – The maximum deviation from one timing operation to the next.
RF – The continuous thermal rating factor (RF) of a current transformer. The RF value is multiplied by the rated primary current of the current transformer to give the maximum primary current that can be handled continuously by the current transformer without exceeding the limiting temperature rise at an ambient temperature of 30° C.
RMS – The effective value of alternating current or voltage. The RMS (Root Mean Square) value equates an ac signal to a dc signal which provides the same power transfer.
Rogowski Coil – The Rogowski coil is an electrical device used for measuring alternating current (AC) or fluctuating current pulses. It consists of a helical coil of wire wrapped around the primary conductor. (Imagine a toy slinky wrapped around the primary conductor). Effectively, each loop of the coil is perpendicular to the primary conductor and the magnetic flux generated by the fluctuating current pulses in the conductor. Using the “right-hand rule”, the magnetic flux lines break the plane of each coil perpendicularly. A voltage is induced in the coils that is proportional to the rate of change of current in the conductor (dv/ dt). Integrating the resulting voltage provides a measurement of the current in the primary conductor. (http://en.wikipedia.org/wiki/Rogowski_coil)
Advantages of a Rogowski coil sensor are;
- The sensor can be made open-ended/ split-core and flexible, allowing it to be wrapped around a live conductor without requiring taking the primary conductor off-line.
- The coil has an air core rather than an magnetic core, hence the low inductance allows faster response to fast-changing currents.
- Highly linear response to large primary current changes since it does not have an magnetic core that can saturate.
- A correctly formed Rogowski coil, with equally spaced windings, is largely immune to electromagnetic interference.
- The coil’s air core does not store energy unlike a magnetic core.
RTD – Resistive Temperature Device or Resistive Temperature Detectors. These temperature sensing devices depend upon the relationship between the resistance of the sensor element and temperature to determine the ambient temperature. The most common industry sensor incorporates a platinum element, with a nominal resistance of 100 ohms at 0°C (commonly referred to as a Pt-100 sensor). These sensors offer excellent stability, repeatability and accuracy. Relatively impervious to electrical noise, they are suitable for noisy industrial applications.
Self Powered – The power required for correct operation of a transducer is supplied via the line being measured.
Separately Powered – The power required for correct operation of a transducer is supplied via an external or auxiliary power source, rather than via the line being measured.
Setting Accuracy – The ability to accurately set a knob, switch, or other adjustment to the time delay, or other monitored parameter.
Self Inductance – Self inductance is where the changing magnetic field of a circuit induces an opposing voltage in the same circuit. The rate of change of the current in the circuit and the topography of the circuit (e.g. straight versus coil) will determine the magnitude of the self induced voltage (V induced = self inductance factor * dA/ dt).
Sintered Ferrite – A ceramic composite powder composed of iron (FE) and barium oxide or strontium oxide which has been die pressed and fired (sintered) in a high temperature oven. The “soft” version of the sintered ferrite does not retain its magnetism when the magnetic field is removed. Transformer cores manufactured from this type of material are incorporated into high performance transformer applications.
Snubber Network – A form of suppression network which consists of a series connected resistor and capacitor connected in parallel with the output device. Helps to limit the maximum rate of rise of a voltage. Used to prevent false turn-on of solid state outputs.
Snubber – A resistance/capacitor or diode/resistor circuit used to dissipate transient energy peaks.
Temperature Measurement Device, Bimetallic – A bimetallic measuring device uses the principle that different metals have different rates of thermal expansion. When two metal strips that have been bonded together are heated, one side will expand faster than the other resulting in the pair bending. The angle of the bend can be translated into a temperature reading. Relative to other technologies, these devices are not very accurate. However, they are portable and do not require a power source.
Temperature Measurement Device, Resistive -A resistive temperature device (RTD) uses the principle that electrical resistance of a material changes as the temperature changes. As the temperature rises, the resistance rises in the metal more or less linearly.
Temperature Measurement Device, Thermistor – A thermistor uses the principle that electrical resistance of a material changes as the temperature changes. As the temperature rises, the resistance in a ceramic semiconductor drops nonlinearly with the change in temperature.
Temperature Measurement Device, Thermocouple -A thermocouple uses the principle that when certain materials are bonded together at one end, changes in temperature results in a change in the electromotive force (voltage) between the opposite ends. As the temperature rises, the output emf rises, though not linearly with the change in temperature.
Thermistor – See – Temperature Measurement Device, Thermistor
Thermocouple – See – Temperature Measurement Device, Thermocouple
Thermowell – A thermowell is a pressure tight enclosure designed to accept a temperature sensing element and provide a means to insert that element into a vessel or pipe. A thermowell acts as a barrier between a process medium and the sensing element of a temperature measuring device. It protects against corrosive process media, as well as media contained under pressure or flowing at a high velocity. A thermowell also allows the sensing element to be removed from the application while maintaining a closed system.
Transducer, Current – A device for converting an Alternating Current (AC) electrical signal into a useable DC voltage or current signal for measurement purposes.
Transducer, Pressure – A device for converting a pressure measurement into a useable DC current or voltage signal for measurement purposes.
Transducer, Temperature – A device for converting a temperature measurement into a useable DC current or voltage signal for measurement purposes.
Transducer, Voltage – A device for converting an Alternating Current (AC) electrical signal into a useable DC voltage for measurement purposes.
Total Harmonic Distortion – The ratio between the apparent power associated with higher order harmonics divided by the apparent power associated with the fundamental harmonic.
Transient – Term used to describe power disturbances such as surge, spike, RF (radio frequency) interference, harmonics.
True RMS Amps – The effective value of an ac signal. For an amp signal, true RMS is a precise method of stating the amp value regardless of waveform distortion. An ac measurement which is equal in power transfer to a corresponding dc current.
True RMS Volts – The effective value of an ac signal. For a voltage signal, true RMS is a precise method of stating the voltage value regardless of waveform distortion. An ac measurement which is equal in power transfer to a corresponding dc voltage.
TVS – Transient Voltage Suppression diode is an electrical component used to protect electrical circuits against voltage surges. The bi-directional diode is connected between the two lines to be protected. As long as the two line voltages are in equilibrium the TVS is a high resistance path between the two lines. If a line voltage exceeds the designed threshold, the resistance decreases providing a path to second line effectively clamping the line voltage. The TVS bi-directional diode is typically incorporated into either a clamp-on current transformer or split-core current transformer with a secondary current output. The incorporation across the secondary output dissipates any stored energy should the current transformer be opened while live.
UL 94 – UL Subject 94 is a flammability test. This test is meant to describe and quantify the flammability of plastic materials when exposed to a flame and heat.
UL 94 V-0 – Flammability test rating – highest rating for a vertical burn test (flame extinguished within 10 seconds and no flaming drip).
UL 94 V-1 – Flammability test rating (flame extinguished within 60 seconds and no flaming drip).
UL 94 V-2 – Flammability test rating (flame extinguished within 60 seconds, flaming drips are allowed).
UL 94 H-B – Flammability test rating, horizontal burn – lowest rating (flame slow moving or self extinguishing).
Unbalanced Loads – Refers to an unequal loading of the phases in a three phase system. Imbalances could be the result of unequal resistive or inductive loads on each phase.
Watt – Unit of electrical power. WATTS=E*I*PF
VA – The product of the RMS voltage applied to a circuit and the RMS current (amperes) flowing through it.
VAR (Volt-Amperes Reactive) – The unit of reactive power as opposed to real power (watts)
Wiki – WEB based collaborative software which permits invited users to edit or add material to a common project. An example is the wiki encyclopedia project (en.wikipedia.org/wiki/main_page).
Other uses include; research & development projects, project management, etc.
Zigzag Transformer – A special purpose transformer that has two primary windings for each phase but no secondary windings. Applications include; a) deriving an earth reference point in ungrounded electrical distribution networks, enabling the detection of earth fault currents and b) the detection/ control of harmonic currents in ungrounded electrical distribution networks.