The problems with calorie counting
Agilent has it's own VEE software competing on the same field. When you use your ohmmeter to measure the resistance of a wire you touch one meter lead to each end of the wire and you get a resistance measurment. Oscilloscope bandwidth is generally listed as the dB point in oscilloscope frequency response. With such oscilloscopes, the true pulse shape remains a mystery. Downside of FET probes are that they are typically expensive and need operating power to work either supplied by oscilloscope using properietary methods or powered with batteries. A unidirectional coupler has available terminals or connections for sampling only one direction of transmission; a bidirectional coupler has available terminals for sampling both directions.
The new design does not -- the money has to be folded. I don't have a problem with the quality of the plastic sack; I have issue with the design of the sack. The purposes for which I used the snack-pak sacks are no longer being met. I'm going to look for the old standby because it's kid friendly. Manaphraim, March 18, My store is Tomball, Tx. The store only carried them for a short time and I was only able to purchase 2 boxes. I LOVE these baggies! I am having to search all over to try and find them.
Please make these are available in all stores! Carla, March 25, I bought these bags originally to carry extra meds in my purse much more convenient than carrying the whole bottle. Since the opening in on the vertical short side , less likely to spill pills everywhere. My toddler granddaughter has her snacks in her portion bags. But the best use of these bags is for storing precut veggies that I keep in my freezer. These are ready for quick additions to soup, stew, meatloaf, sauces.
Armybear, March 2, As far as for snacks, these are horrible. They are only good for a limited type of items, the opening is very small. I understand that you tried to produce a more specialized bag and the measurement markings is nice. However if so, please still offer the original rectangular bags. Lily, July 28, The Great Value Portion Pack Snack Bags are a specialty snacking bag that is, by design, made for measuring snacks to be eaten on the go, such as nuts, small crackers, raisins, etc.
We are sorry you did not like them. The Great Value Square Snack bags may be a good option for you. They are slightly larger than the rectangular snack bag and are easier to fill and close, especially with larger snack items such as carrots or graham crackers. Where are my OLD snack bags?!? What in the world was someone thinking when they redesigned the snack bags? The wide opening on the long side has been changed to the small end.
Seriously - you have to use a teaspoon to get anything in these. The old design was perfect for half a sandwich or just a few cherry tomatoes or grapes, but this "improved" design is unusable and impractical. Bring back the wide opening you can actually use. The rectangular snack bags have been replaced with a new square snack bag which is slightly larger and 'square' vs rectangular which is more convenient to fill and holds more of most items.
This is a gas filled tube, to which a voltage of several V is applied. Normally, the gas insulates and no current is drawn. When a radiation particle or quantum passes the tube, it triggers a gas discharge, i.
The resulting current impulse can be amplified and made visible or hearable "clicking". Glas mantle tubes are only suitable for beta and gamma rays, as any alphas are absorbed in the glass. Window tubes have a window usually at one end , which is sealed with a very thin foil or mica.
Alphas can penetrate this window, and thus be detected, as well as betas and gammas. There are also diode based radioactive dosage meters in use. Adding heat to a system causes its temperature to rise. While there is no maximum theoretically reachable temperature, there is a minimum temperature, known as absolute zero, at which all molecular motion stops. Temperatures are commonly measured in the Kelvin or Celsius scales, with Fahrenheit still in common use in the Unites States.
There are many ways to measure temperature elecronically. A thermocouple is a very commonly used sensor for measuring temperature. It consists of two dissimilar metals, joined together at one end, which produce a small unique voltage at a given temperature. This voltage is measured and interpreted by a thermocouple thermometer. In practical applications the so called cold side of the junction is kept close to ambient temperature by bonding it to a temperature stable mass.
The hot side of the junction is exposed to the temperature to be measured. Because thermocouples measure in wide temperature ranges and can be relatively rugged, they are very often used in industry. Thermocouple is a A temperature sensing device made by joining two dissimilar metals.
This junction produces an electrical voltage in proportion to the difference in temperature between the hot junction sensing junction and the leadwire connection to the instrument cold junction. In typical applications the the hot side is in the end of sensor wire and the cold juction in the temperature measurement device near the sensor connector. In many cheap meters this cold junction is just in the same temperature as the meter itself, and it's temperature is measured in other means to compensate the effect of changes in cold junction temperature.
Thermocouple detectors have low impedance. Thermocouples are available in different combinations of metals or calibrations. The four most common calibrations are J, K, T and E. Each calibration has a different temperature range and environment.
Propably the most commonly used type is K-type thermocouple, which is a Ni-Cr-sensor very suiable for degress celsius temteperature measurements can be used from to celsius. The accuracy of any circuit or system that uses a thermocouple to determine the temperature of a process is limited by the accuracy of the method used to perform cold-junction compensation. In a thermocouple measurement, two wires of dissimilar metal join together at the "hot," or measurement, junction. The isothermal termination of the thermocouple wires provides a second "cold," or reference, junction.
The potential across the thermocouple is proportional to the temperature difference between the two junctions. Thus, to determine the absolute temperature of the hot junction, you must also know the absolute temperature of the cold junction. Resistance Temperature Detector RTD is a sensor that uses the resistance temperature characteristic to measure temperature. There are two basic types of RTDs: A resistive thermal device RTD can measure temperatures as high as ?
C over a great distance and without expensive signal conditioning. The most popular RTD is a standardized platinum temperature sensor called the PT, which exhibits ohms resistance at 0? C and a linear temperature coefficient of 0. C characteristic appears almost linear over a narrow range. A PRTD's transfer function of resistance vs. C, are approximated by the equation: Unlike thermocouples, which deliver voltages that represent the difference between two temperatures, the resistance of an RTD represents the absolute temperature of that resistance.
Measurement is typically accomplished by driving a current of 1mA to 2mA through the sensor and measuring the voltage drop across it. Also semiconductors can be used as termperature sensors because semiconductor PN junction characteristics change when temperature changes. This change is well defined and this can be used in some temperature measurement applications. The temperature - versus - bulk resistance characteristics of semiconductor materials allow the manufacture of simple temperature sensors using standard silicon semiconductor fabrication equipment.
The ordinary semiconductor diode may be used as a temperature sensor because a forward biased voltage across a silicon diode has a temperature coefficient of about 2. C and is reasonably linear. The forward basing can be done with for example around 1 mA current through the diode.
To improve the performance of the diode as a temperature sensor, two diode voltages can be measured with two different currents typically selected to be about 1: The transistor sensor is used in diode mode by connecting the base and collector together or sensor is wired between base and emitter.
Semiconductor temperature sensors are available from a number of manufacturers. There are no generic types. The semiconductor or IC for integrated circuit temperature sensor is an electronic device fabricated in a similar way to other modern electronic semiconductor components such as microprocessors. C typical , low cost, good accuracy if calibrated but also poor interchangeability. In general, the semiconductor temperature sensor is best suited for embedded applications - that is, for use within equipment.
This is because they tend to be electrically and mechanically more delicate than most other temperature sensor types. The "out of the box" or interchangeability accuracy of most semiconductor temperature sensors is not particularly good.
If individual sensors are calibrated, significantly better measurement accuracy is possible tyically a two point calibration or three point calibration is used. Due to the high sensitivity of some sensors, they can be very good in measuring small temperature changes as opposed to absolute measurement.
Bimetallic thermometers are contact temperature sensors found in several forms if you know where to look, e. They typically consist of a strip of bi-metal that has some electrical contacts affixed to it. The temperature changes cause the strip to bend, making or breaking the connection as needed.
You will often find long bimetallic strips coiled into spirals. This is the typical layout of a backyard dial thermometer. By coiling a very long strip it becomes much more sensitive to small temperature changes. In some applications temperature sensing needs to be done without contact to the measured subject. Those measurements use infrared IR techniques.
Radiation Thermometers Pyrometers, if you will are non-contact temperature sensors that measure temperature from the amount of thermal electromagnetic radiation received from a spot on the object of measurement.
There are two types of commonly used sensors for this kind of applicatons: Pyroelectric Infrared Detectors and Thermopile detectors. Pyroelectric Infrared Detectors PIR convert the changes in incoming infrared light to electric signals. The pyroelectric detectors output is proportional to rate of change of incident radiation.
This means that pyroelectric detectors can only be used to detect temperature changes. This kind of PIR sensors are used for example in movement detectors where they sense the moving hot object like human through special optics this optics makes the movement of hot object change the radiation that gets to sensor change sharply when object moves. Pyroelectric detectors have very high impedance requiring an internal impedance converting buffer to make them useable.
Thermopile detector output is proportional to incident radiation. A thermopile is a number of thermocouples connected in series. The so called cold side of the junction is kept close to ambient temperature by bonding it to a temperature stable mass.
The hot side of the junction is exposed to incident radiation. Some thermopile sensors have a built-in thermistor which provides measurement of the ambient temperature thus allowing the temperature of the target to be calculated. A thermopile sensor generates a voltage, which is proportional to the incident infrared IR radiation power. Because every object emits IR radiation with a power, which is a strict function of its temperature, one can deduct the object?
This method is called pyrometry. Thermopile-type infrared and thermal detectors are used in a number of applications, including infrared spectroscopy, radiometry, security systems, and many consumer products.
Although they do not provide vision-quality images as in the case of quantum detectors, thermopiles are still attractive for many low-cost commercial and industrial applications, mainly because they do not need cooling for operation and the technologies are relativly simple.
Thermopile detectors have low impedance. In addition to those some applications use Thermal Infrared imaging camera. Thermal Infrared imaging camera is a camera that responds to the infrared signals instead of normal light. Thermal infrared imaging cameras are detector and precision optics platforms that give us a visual representation of infrared energy emitted by all objects.
Typical applications for this type of cameras are night vision,wildlife observation, search and rescue, victim location, wild fire recon, predictive maintenance in power transmission and machinery, carona detection, process control and printed Circuit Board evaluation.
Depending the applications the IR radiation can be shown as normal grayscale video or through real time color infrared output. The color conversion converts different radiation intensities to different colors for easy visual inspection of picture. With a well calibrated camera, those different colors on picture can be directly mapped to different temperatures. Thermal infrared imaging cameras are expensive devices bceause they need special imaging sensors that needs to be cooled down to make them operate correctly.
This is the Seebeck Effect, discovered by Thomas Seebeck in The effect is multiplied when there are a number of junctions in series in the circuit, with alternate junctions in close thermal contact with each other. Schematics, mounting instructions and step-by-step instructions included. Rate this link ECEFast Technical Papers - A selection of temperature measurement information document platinum resistance temperature detectors, thermocouple fundamentals, noncontact thermometers and infrared systems.
Also information on water characteristics measurement conductivity, exygen, pH. This technique is a very good way to detect the temperature of a person's eardrum.
Rate this link International Thermocouple Colour Codes: Rate this link Measuring temperatures on computer chips with speed and accuracy-a new approach using silicon sensors and off-chip processing - Silicon sensors are becoming increasingly important transducers in electronic systems.
As systems become more complex, more compact, and denser-and run faster and hotter-it becomes increasingly vital to monitor critical temperatures. Traditional sensor techniques, such as thermocouples, thermistors, and RTDs, are now being displaced by silicon sensors, with their ease of integration and use. Silicon sensors, on the other hand, are linear, accurate, low-cost, and can be integrated on the same IC as amplifiers and any other required processing functions.
The actual sensing element in a silicon sensor is a simple P-N transistor junction. C and this fact may be used to develop a temperature measuring system. Rate this link Omega Technial Reference Section - Lots of technical documents on temperature measurement sensors. Rate this link Pyroelectric detectors - Pyroelectric Infrared Detectors PIR convert the changes in incoming infrared light to electric signals.
Rate this link Remote diodes yield accurate temperature measurements - All of today's PC designs require thermal management. Heat generation is a problem for PC-system designers.
To prevent failures, you must incorporate thermal-management features in your design. You can control temperatures by, for example, lowering device voltages and reducing clock rates so that devices generate less heat, or by increasing airflow so that the system can better dissipate heat into its environment.
Because die temperature is a critical parameter, some devices incorporate a means to allow you to measure it. It is aimed at engineer, student, scientist, and technologist alike.
Rate this link Temperatures. Rate this link Thermocouples Introduction - The Thermocouple is a thermoelectric temperature sensor which consists of two dissimilar metallic wires, e. These two wires are connected at two different junctions, one for temperature measurement and the other for reference. Rate this link Track multisite temperatures on your PC - This low-cost circuit allows you to track four remote temperatures with thermistor sensors through the parallel port on your PC.
C and a resolution of better than? VBE for a bipolar transistor is a linear function of the absolute Kelvin temperature, T. You can use this truism to make accurate temperature measurements. The circuit provides analogue voltage output.
They are used in a wide variety of temperature measurement and control instrumentation. Rate this link Digital Remote Thermometer - Remote sensor sends data via mains supply, temperature range The Dallas Semiconductor DS digital thermometer allows measurement resolution as fine as 0.
C in digital form and with linear response. The accuracy specification is only 2? C, but you can improve this figure by careful calibration. Rate this link Qiozl's Temperature Sensor Project - Just a handful of components builds an 8-pin microcontroller based circuit for temperature logging via a serial port; small, fast, and acceptably accurate.
But most thermistors' resistance-versus-temperature characteristics are highly nonlinear and need correction for applications that require a linear response. Using a thermistor as a sensor, the simple circuit presented in this article provides a time period varying linearly with temperature with a nonlinearity error of less than 0. You can use a frequency counter to convert the period into a digital output.
Fortunately, several low-cost temperature-sensing integrated circuits ICs are easy to isolate. This application note shows two approaches to isolating temperature sensors. Rate this link Selecting temperature sensors Temperature Sensor ICs Simplify Designs - When you set out to select a temperature sensor, you are no longer limited to either an analog-output or a digital-output device.
There is now a broad selection of sensor types, one of which should match your system's needs. Rate this link Tradeoffs in Selecting IC Temperature Sensors - A discussion of IC temperature sensors has become timely and important because electronic systems are increasingly dense, power-hungry, and hot. Temperature sensors also have a lot of gadget appeal. Many ICs perform highly abstract functions. Included are seven segment decoders, display drivers, a reference, and a clock.
It contains an internal voltage reference, high isolation analog switches, sequential control logic, and the display drivers. The auto-zero adjust ensures zero reading for 0 volts input. This how this circuit uses that IC to make a voltage meter. Rate this link Digital Volt meter with video output - This design awarded the third international prize in the Elektor Electronics Microprocessor and Microcontrollers Design Contest.
Rate this link Circuit yields accurate absolute values - This circuit delivers the absolute value of the input signal with an accuracy better than 10 ppm of the full-scale range. This technique usually works well unless your design requires operation higher than a few kilohertz. In designs requiring such operation, the accuracy of the circuit severely deteriorates unless at least one of the amplifiers has a high slew rate and frequency response extending to tens or even hundreds of megahertz.
This circuit uses a moderately fast, inexpensive comparator instead of a high-slew-rate op amp to implement the peak detector. This circuit provides wide bandwidth and high accuracy without the use of precision components, and it's simple and inexpensive.
It is not an "Average" voltage and its mathematical relationship to peak voltage varies depending on the type of waveform. By definition, RMS Value, also called the effective or heating value of AC, is equivalent to a DC voltage that would provide the same amount of heat generation in a resistor as the AC voltage would if applied to that same resistor. True RMS allows the user to obtain accurate measurements of voltage at any waveform.
True RMS meter work for non-sinusoidal AC voltage and current waveform found in controls and circuits. Normally True RMS reading meters are very expensive. The typical multi-meter is not a True RMS reading meter.
It does this by measuring average voltage and multiplying by 1. Trying to use this type of meter with any waveform other than a sine wave will result in erroneous RMS readings. Improper measurement can easily lead someone to believe that a modified sinewave or square wave inverter is not putting out its rated power. A few handy things to keep in mind about RMS values that apply when dealing with a sine wave, are as follows: Peak Volts AC x.
As a result it will only produce misleading voltage readings when trying to measure anything other than a DC signal or sine wave. This will be indicated by a flashing light-emitting diode LED. This circuit is based on two LEDs and one lamp. Due to the lamp's filament behaviour, any voltage in the 1. For those high voltage, special techniques and probes are needed. Electronic high voltage meters - Common voltmeters, digital or analog, usually range to some hundred volts maximum.
Rate this link Measuring high voltages by spark length - The simplest way to get at least a rough value of tension is to measure the maximum distance the voltage can arc over. The maximum spark length is determined by applying the high voltage to a pair of electrodes and bringing the electrodes closer to each other until a spark jumps over.
Rate this link Current measurements Measuring electrical current can be done using many methods. There are three rival technologies that are typically used for measuring current: Each have attributes that differentiate them on a cost versus performance scale.
A general characteristics of different current measurement methods: The voltage drop over thisresistor is determined by the current and the resistor value. If you select a small resistence, you do not cause much voltage drop over it, so measung does not considerably affectthe measured circuit.
When measuring high currents on mains power cables devices called "current transformers" are used. Their main purpose is to produce, from the primary current, a proportional secondary current that can easily be measured or used to control various circuits.
The primary winding is connected in series with the source current to be measured, while the secondary winding is normally connected to a meter, relay, or a burden resistor to develop a low level voltage that is amplified for control purposes.
When using just one wire going through the core, that wire can easily made thick enough to be able to handle large currents.
Current transformers are relatively simple to implement and are passive devicesthat do not require driving circuitry to operate. The primary current AC will generate a magnetic field that is coupled into a secondary coil by Faraday's Law. The magnitude of the secondary current is proportional to the number of turns in the coil, which is typically as high as turns or even more.
The secondary current is then sensed through a sense resistor to convert the output into a voltage. The voltage measured over selected burden resistor resistor connected between the current transformer output coil outputs gives the indicationof the current voltage directly proportional to the current. The selected burden resistor value is usually defined with help of transformer data and experimenting.
When a suitable burden resistor value is selected, a general experimental transformation ratio is calculated for thisapplication ratio from input current to output voltage with given current transformer and burden resistor. When using current transformers on high current circuits, make sure that the current transformer is never run without a proper burden resistor. If there is a high current going on transformer primary and many turns on secondary, the open circuit voltage of current transformer can become very high, even to several kilovolts range that can cause operation danger and damage the current transformer secondary insulation.
In current transformer applications where the measuring equipment needs to be service, the output of current transformer should be short circuited before removing the burden resistor load. In some SMPS designs current transformer usually made using a ferrite toroid helps to track the current in the control circuit's feedback loop. This current is then used to determine how the future behavior of the SMPS will be modified.
Many clamp-on multimeters and clamp-on current measuring adapters that can measure AC current are built as current transformers. A simple current adaptor can only consist of the transformer core which can be opened , the transformer secondary coil and suitable burden resistor.
Some clamp-on multimeters can also measure DC currents. The hall sensor in the air gap measures the magnetic field cause by the wire running through the toroidal core. There are two techniques for sensing current using Hall effect devices: In an open loop topology, the Hall element output is simply amplified and the output is read as a voltage that represents the measured current through a scaling.
In a closed loop topology, the output of the Hall element drives a secondary coil that will generate a magnetic field to cancel the primary current field.
The secondary current, scaled proportional to the primary current by the secondary coil ratio, can then be measured as voltage across a sense resistor. By keeping the resultant field at zero, the errors associated with offset drift, sensitivity drift and saturation of the magnetic core will also be effectively canceled. Closed-loop Hall effect current sensors also provide the fastest response times. However, with a secondary coil that may be needed to drive up to several milli-amps of current, power consumption is much higher in closed loop Hall effect devices than open loop topologies.
Current clamp meters and clamp adapters are especially suited to measure DC and AC currents, in all instruments and systems, without interruption of the circuit. In practice there are many systems where it is not possible or safe to disconnect systems for the purpose of measuring the current flowing. Therefore, with the use of a Clamp Meter the current can be measured without any interruption whatsoever. Generally clamp-on multimeters need the toroidal type core to be closed to get measurements.
Lately there has become available "open jaw" style Electrical Tester for measuring current using measurement device which does not need the fully closed core.
Clamps and clamp adapters are easy to use. The conductor is completely surrounded by the current clamp. The measurement value appears on the analogue or digital display and can be read immediately. Most cheap clamp meters are designed to measure the current value of current that have sinewave shape. The RMS value is important for all non-sinus shaped currents, e. Generally, the measurement value displayed on conventional clamps is smaller than the actual measurement current present when the waveform is non-sinusoidal.
Clamp-on nmultimeters are typically designed to measure currents in range from few amperes to several hundred amperes some meter go beyond A. The cheapest clamp-on meters have measuring resolution of around mA.
There are more expensive meters that have higher resolution like 10 mA or 1 mA suitable to measure for example current industrial mA current loops. High resolution mini current clamps for leakage currents from 10? Leakage currents which do not return via an electrical conductor e.
N, PE can be quickly, easily and safely measured by surrounding all active conductors e. With traditional clamp-on current meters, measurements can only be made on single conductors.
If you need to measure current in multipair cables for example mains cables , this usually needs covers to be moved to gain access to individual wires. To measure the current consumption of an instrument, the individual wires of a cable had to be opened using e. From the safety aspect, this procedure was not without problems and relatively difficult to perform. Some new special multimeters can measures current in multi-core cables and power cords without the need to split them.
This kind of multimeter use techologies which are called dending on manufacturer with names like Flexiclamp, multi-core digital clampmeter, duplex clamp and SMF Technology.
Different manufacturers use slightly different technologies. Unitest uses in their duplex clamp technology that has several sensor coils are positioned at a certain distance and direction. With this coil layout, the field direction of the current within a lead can be filtered with respect to the neighbouring lead.
Thus, current measurement within a multi-lead cable is possible, without opening. A new technology for AC current measuring is Rogowski coil. Rogowski coil current transducers can measure alternating currents in a frequency range from less than 0. Their measurement range is impressive ranging from a few milliamps to over 1 million amps. These transducers have an excellent transient response capability and they can be used for measurements on very large or unusually-shaped conductors.
A Rogowski coil is an 'air-cored' toroidal coil placed round the conductor. The alternating magnetic field produced by the current induces a voltage in the coil which is proportional to the rate of change of current. The combination of a coil and an integrator provides an exceptionally versatile current-measuring system which can be designed to accommodate a vast range of frequencies, current levels and conductor sizes.
The output is independent of frequency, has an accurate phase response and can measure complex current waveforms and transients. One of the most important properties of a Rogowski coil measuring system is that it is inherently linear.
The coil contains no saturable components and the output increases linearly in proportion to current right up to the operating limit determined by voltage breakdown. The integrator is also inherently linear up to the point where the electronics saturates. Linearity makes Rogowski coils easy to calibrate because a transducer can be calibrated at any convenient current level and the calibration will be accurate for all currents including very large ones.
Also, because of their linearity, the transducers have a very wide dynamic range and an excellent transient response. Some designs of coil can be fitted on the conductor without the need to disconnect the conductor.
Most flexible coils can be fitted this way and it is also possible to build split rigid coils. When measuring current on mains wires please note that most AC current meters are designed to give right current ratings only when they are connected to pure sinusoidal mains current.
Pulse-width motor control systems, SCR and triac controllers and switchmode power supplies, for example, add high frequency HF components to the 50Hz mains that can cause false readings on traditional multimeters. Solar Panel Current Meter - This circuit is used to measure the current from a solar panel. It has very low power loss for currents in the A range. It also works as a general purpose DC current meter. The circuit can be used on either the positive or negative side of a DC circuit.
The circuit works with DC circuits at any practical voltage. The coil output voltage is integrated electronically so that the output from the integrator is a voltage that accurately reproduces the current waveform of the wire going through the coil. This document describes both open loop and closed loop Hall current sensors operation. Rate this link Measure power-on current transients on ac line - For any electronic or electrical system, you usually determine the ac-line fuse rating based on the steady-state current.
However, the power-on current surge is an important parameter in determining the fuse's I 2 t rating. The I 2 t rating is a measure of the energy required to blow a fuse in pulsed conditions.
Rate this link Picoammeter circuit with 4 ranges - This circuit uses a CA BiMOS op amp to form a picoammeter with 4 ranges and exceptionally low input current typically 0.
The probe is "clamped" around the current carrying conductor to perform non contact current measurement. This technology allows "open jaw" and "multi-core digital clampmeter".
The key to the performance of this new sensor is a series of planer magnetic coils placed in a specified layout around the conductor. The magnetic field created by the current in the conductor induces a voltage in the magnetic coils, which is proportional to the magnetic field of the conductor.
Rate this link Field Adjustment of Current Transformer Ratio - The ratio of current transformers can be field adjusted to fulfill the needs of the application. Passing more secondary turns or more primary turns through the window will increase or decrease the turns ratio. Rate this link Selecting ANSI Class Metering Current Transformers - One of the most common uses of current transformers are in metering and power usage, where a 5 Amp secondary current transformer is applied to a panel meter or a power meter for displaying amperage or recording power.
When extremely accurate measurement is required, or when revenue is generated from a power meter, ANSI class current transformers are generally selected. Creating DC from an AC source creates problems with diode voltage drops and the variances over temperature and current.
This circuit provides an accurate method for creating this DC signal. In this example, a compressor current is sensed, and when it reaches a selected set point, the circuit turns on a relay, which controls a fan motor. The circuit is generated with a minimum number of parts, and includes hysteresis.
Rate this link An Analysis of Current Transformer Ratio and Phase Angle Error - A technical discussion of the current transformers including equivalent circuits, phasor diagrams and Thevenin equivalents. Rate this link Application Guide - A general application guide that covers most areas of electrical current monitoring using current and voltage transformers. The primary purpose of this guide is to give the reader a basic understanding of how to apply instrument transformers in a practical way while observing good engineering practice.
A special effort will be made to keep to a minimum technical terms and language. The transducer was tested with currents from a tuned LC circuit for frequencies between 0. The current sensing requirement is a more difficult problem. Not only does the current sensor require a wider measurement dynamic range, it also needs to handle a wider frequency range because of the rich harmonic contents in the current waveform.
They could not be used for current measurements because coil output voltage and power were not sufficient to drive measuring equipment. Rogowski coils have many advantages over conventional current transformers. Rate this link Using Rogowski coils for transient current measurements - In recent years the Rogowski-coil method of measuring electric current has developed from a "laboratory curiosity" to a versatile measuring system with many applications throughout industry and in research.
The technique possesses many features which offer an advantage over iron-cored current measuring devices and these are well illustrated by considering how it can be used for measuring transient currents The paper describes the principle of operation of Rogowski coils and the practical aspects of using them and gives several examples of their use in making transient measurements.
But metering technologies have been the Cinderellas of energy infrastructure - they work hard as cash registers for the utilities, using electromechanical designs which have altered little for the past 30 years. However, the utility market is changing, and as the cost of digital microelectronic devices comes down, the opportunities offered by solid-state meters are looking increasingly attractive for more intelligent metering systems.
On the National Spherical Torus Experiment NSTX , the plasma current Rogowski Loop had the constraints of the very limited space available on the center stack, volt isolation and flexibility requirements. This paper tells about the coil design. When the cables become polluted and wet, a conductive layer is formed on the cables, and leakage currents are induced on their leading to dry-band arcing.
Knowledge of the leakage current levels on the cable surface before dry-band arcing can be used to predict cable failure. Monitoring the leakage current can also yield information on the aging of the cable. This paper presents a review of three different current sensors that can be used on ADSS cables, which include a simple shunt resistor, an active Rogowski coil, and a double core sensor. Rate this link Rogowski Coils - Rogowski coils are used for measuring alternating current.
They work by sensing the magnetic field caused by the current without the need to make an electrical contact with the conductor. These coils have been used in various forms for detecting and measuring electric currents for decades but it is only in recent years that their potential is being realised on a commercial scale.
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