Article for Elektronik Informationen
Isabellenhütte Heusler GmbH & Co. KG
14 August 2008 Shunts past and prent
Possibilities and applications of modern resistors
祝福英语During the last few decades, shunts had to be improved immenly to stay in u. Today, they are better than ever and constitute a component very much in demand in current applications, such as high-side current measurement in hybrid and electric vehicles. But not all shunts are alike: this article illustrates tho aspects that are most important for design engineers when choosing the best shunt for their purpo.
Once again, the latest crude oil cost explosion showed the importance of efficient primary energy consumption in all areas of our national economy. Electric energy is valuable and should be ud especially economically and efficiently, making it necessary to measure and control electric current.
There is a large number of different nsors using various physical principles for measuring electric current. Measuring devices of industrial importance include current-nsing resistors (shunts) and the l
arge group of nsors using the magnetic field generated by the measured current, among them current transformers, Hall effect nsors and GMR nsors. Niche applications (e.g. extremely high currents or isolation voltages) also u optical methods. Design engineers often find it difficult to determine which current nsor is best suited for their applications. Data sheets often do not include complete performance data such as linearity, absolute accuracy, temperature dependency and load respon, or the values are not easily comparable to tho of other nsors. Engineers need to determine their application's benchmarking data and then find the nsor best suited to their current, frequency and application temperature range. They also have to consider resolution, interference resistance, offt, long-term behaviour, isolation, construction volume, current drain and how the nsors are installed. All this turns choosing a suitable current nsor into a complicated and often underestimated task.
Isolated measurement almost without loss is one of the indisputable advantages of magnetic nsors, but this is only true for direct-indicating nsors (such as Hall effect nsors), which are often only suitable for approximate measurements due to insufficient accuracy, high offt and high temperature dependency. Compensation converters (especially in a high current area over 100 A) also require a measurement current and a substantial metrological effort in the condary circuit, in addition to being rather large.
In spite of claims to the contrary, shunts are in most cas the best solution for low voltage applications (e.g. the automotive ctor) or low-side measurements (e.g. houhold appliances). SMD version precision shunts with their high accuracy, low temperature dependency, extremely stable long-term behaviour and high load capacity in particular cannot be compared with older leaded resistors. Furthermore they can be automatically equipped, are small and comparatively inexpensive (figure 1: old and new).
Figure 1: Conventional leaded resistors compared to new SMD precision resistors
On Our Way to Finding the Perfect Current Sensor
Customers‟ expectations can be generally described as
R R(T, t, P, I, Hz, B . . . ),
meaning that the resistance value should be largely uninfluenced by any potential physical parameters such as temperature, time, performance, current, frequency, magnetic field and others.
U = R*I + Uth + Uofft + Uind + Uv + …
applies for the potential drop across at the resistor according to Ohm's law.
蒜怎么种The additional components constitute error voltages which may cau substantial measuring errors in the form of current-independent offt, especially with low-impedance resistors and their low measurement voltages.
When there is a temperature difference between contacts, using a …wrong‟ material that is not thermoelectrically adapted to the world of Cu (such as constantan, CuNi44, which is still often in u), will result in thermoelectric potential Uth of 0.1 to 1 mV. The worst problem with this is that in the ca of direct current this Peltier effect in the material will be the cau of a temperature difference and, as a result, thermoelectric potential, making errors unavoidable. This fact is unknown to many developers. In the past, resistors with impedances as high as possible were ud to increa the distance to error voltages, leading in turn to incread power dissipation and all other disadvantages connected with this.40厘米等于多少分米
The last decades‟ extreme progress in microelectronics has led to the development of high-performance, compact and inexpensive operation and measuring amplifiers and measuring converters with a low offt potential Uofft, low temperature dependency, low noi and a very low current consumption to allow for an accurate and low-noi measurement even for small voltages.
Induced interference potential can be minimid by the resistors‟ low lf inductance (up to 0.2 nH) and short, low-induction connections between resistor and the measuring system.
Other error voltages Uv may include voltages on the circuit board caud by the supply current that are accidentally included in the measuring circuit. However, careful design can mostly avoid the errors.
爱射As conventional resistors had all of the disadvantages, designers tended to u resistors that were far too large and never working to capacity in the application. Miniaturisation and the u of SMD technology required new and clearly improved components.
A resistor's properties are determined by the following values:
-Technology
寸进尺退的意思(carbon film, thin film, thick film, wire-wrap, foil technology,)
-Resistance material
(thick-film pastes, galvanically isolated layers, sputtering, resistance alloys) -Construction
-Manufacturing method
ISA-Plan-foil technique proved to be the best solution for current nsing resistors (CSR) for values below 10 Ohm, and ISA weld technology for extremely small values below 10mOhm. The precision resistance alloys ud, manganin, zeranin and Isaohm, are prerequisites for the resistors‟ low temperature dependency (figure 2), long-term stability and extremely low thermoelectric potential.
For Isa-Plan technology, a rolled, specially stabilid resistor foil is glued onto a Cu or Al substrate for isolation, structured with acid etching and then ud in a SMD resistor. Becau of its good thermo-conducting properties, the substrate leads to a very low inner thermal resistance, enabling the shunts to work under full load without losing stability or accuracy even at high temperatures. Furthermore, the metal substrate‟s coefficient of expansion is better adapted to the circuit board than that of the conventional ceramic, minimising strain on junctions in the ca of temperature changes when lead-free soldering is ud, therefore guaranteeing high durability.
For the Isa weld technology, electron beam welded bands (Cu-Manganin-Cu) are ud to die-cut extremely low-impedance, inexpensive resistors for high-current applications in SMD versions or for current bar installation in the ca of currents well above 1000 A (2 µOhm to 3 mOhm)
Both manufacturing methods result in precision shunts with largely optimid physical properties that come very clo to the “id eal current nsor.”
Along with recent electronic systems, they make it possible to develop very compact measuring modules with an unprecedented cost-performance-ratio for current measurement and control.
Shunts will also be ud in new mi-conductor systems, e.g. in high-resolution, offt-free voltage transformers for low input voltages in the µV/mV area, transformers with an integrated µC and highly dynamic insulation transformers, in areas that were conventionally rerved for magnetic nsors.
Some examples for applications will be described more cloly in the following:
High Voltage Measurement with Shunt and ISA-ASIC
Until now, current transformers or the DIN shunt (DIN 43 7039) in combination with complicated electronic measuring equipment were ud exclusively in the area of high voltage measurement. The ISA-ASIC or similar offt-free voltage transformers for low-potential measurement make it possible to develop compact, inexpensive and much more accurate modules such as the measuring module shown in figure 3 for very preci and quick direct and alternate current measurements up to 400 A (up to 1,500 A over short periods).
Figure 3: Conventional DIN-Shunt compared to a new measuring module with an Isabellenhütte ISA-ASIC and an Isa weld shunt
Conventional high-current DIN shunts have a potential loss between 60 and 300 mV at nominal current. In a comparison at voltages of 10 mV and less, Isa weld shunt-bad systems are considerably more accurate, smaller and less expensive, with a power dissipation that is six to ten times lower, which in the end was the cau for the DIN standard named above not to be renewed or transformed into a European standard.
The measuring electronic circuit board (ISA-ASIC+µC) is soldered directly to the 100-µOhm Isa weld shunt for extremely short connections between measuring current and measured value acquisition, leading to high interference resistance and quick reactions. The ISA-ASIC is a very accurate, absolutely offt-free 16-bit measuring value acquisition system. Its four input channels and many special features make it perfect for measuring extremely low voltages. For the output of measured current and voltage values, it us a RS232 or RS485 interface for external processing.
Zero offt, very good linearity and low noi make it possible to measure even very small direct currents up to 1 mA in high overlaid alternate currents of more than 100A.
Figure 4 shows puld current measurement of 400 A/300 mc recorded with a sampling rate of 16 kHz. It illustrates that the measured value is in a completely steady state even after only one measuring cycle (<62 µc). Floating measurements for extremely fast current increas of more than 7 kV/mc caud no outliers or interferences. The devices are delivered fully calibrated and have a very high absolute accuracy of (0.05% vMW +/- 25 mA) and a temperature dependency of 50 ppm/K (figure 5.)
By changing the resistance value to only a few µOhm, the current range can be expanded easily to between 5,000 and 10,000A without producing too much lost heat.
High side current measurement
Battery-operated devices and the automotive industry often require current to be measured on the power supply side (high side) (Figure 6). For this, various mi-conductor manufacturers offer inexpensive high-quality ICs with low offt values and variable amplification (differential amplifier or current mirror) to amplify the signal produced by the SMD shunt on the power supply side and transmit it via a µC to the earth side for processing, making it possible to u very low-impedance resistors for currents of up to some 100 A.
Isolated high current measurements for propulsion technology饮的多音字组词
Various mi-conductor manufacturers (e.g. TI, Infineon, Avago or AD) have recently introduced new isolation transformers which, in combination with a shunt, will enable highly
dynamic, insolated current measurement in the area or 500 A. The basic idea is using a 1-bit sigma delta modulator on the high-side together with a 10 to 20 MHz clock transferred over an isolated ction. The result is transferred to the earth side as bit current. Suitable digital signal filters lead to extremely flexible, highly dynamic and accurate motor current measurement and control and enable a fast excess current detection in the µc area. The systems can easily work with extremely fast voltage changes of up to 15 kV/µc as they occur in modern synchronid motor control systems and provide 12-14 bit measured values with sampling rates up to 100 kHz. This method is even more interesting for most recent motor controls already including the programmable filters mentioned above. Together with its compact build and its low power loss and measuring power, this new method leads to an unprecedented cost-performance ratio.
All this will lead to shunts finding their way into another domain traditionally rerved for current transformers on a long-term basis and replacing transformers especially in the areas of high-performance motor controls as in the ca of machine tools, hybrid and electric vehicles, etc.
简笔玫瑰花Captions:
Figure 1: Conventional leaded resistors compared to new SMD precision resistors
Figure 2: Low temperature dependency due to manganin, zeranin and Isaohm
Figure 3 Conventional DIN shunt compared to a new measuring module with an Isabellenhütte ISA-ASIC and an Isa weld shunt
Figure 4: ISA-ASIC puld current measurement
Figure 5: ISA-ASIC proves its high absolute accuracy
Figure 6: High-side current measurement议论文万能开头模板
Figure 7: Shunt replaces converter in high performance engine control
approx. 11,500 characters
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Author: Dr. Ullrich Hetzler
Head of Rearch and Development
Isabellenhütte Heusler GmbH & Co. KG
Company contact:
Dr. Ullrich Hetzler
hetzler@isabellenhuette.de
Tel.: 02771 / 934-242
Press contact:
Michaela Wasnberg
