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Benchmark accuracy finds its way into new markets

14 Nov 2014  | Stephane Rollier, Horst Bezold

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Often, power needs to be measured across three, four or even six channels when testing a multi-channel product such as an inverter for example. For these multi-channel tests, LEM's multi-channel measurement system includes a power supply and transducer connection cables to enable a complete measurement system to be setup within minutes.


Precision motion control
The semiconductor manufacturing process is another application in which current transducers with ultra-high accuracy can be used.

The manufacturing process uses complex photolithographic techniques to image and create the nanoscale structures that form the integrated circuit components used in a chip. The use of a very short wavelength is crucial because the resolution of the process is directly proportional to the wavelength.


Figure 6: A photolithographic scanning stepper.


During the photolithographic process, a scanning stepper moves the silicon wafer through a series of positions so that an identical die or circuit can be etched onto each wafer. Each time an individual die is illuminated, the mask, wafer and light-source must be stationary in relation to each other.

To achieve the nanometre-scale geometries that produce the highest integration of components onto a die, and dice onto a wafer, precise positioning and motion control are essential. Positioning is split over two stages: stepping positioning in which the wafer is moved to a specific die position, and scanning positioning, which controls the movement of the wafer and the photo-mask.

The motion of the scanning stepper is controlled by measuring the drive current in the coil of the linear actuator. As near-perfect synchronisation between the two movements is imperative, a high-precision current measurement with extremely high differential linearity is essential.

An ultra-high precision DC current transducer offers the precision and differential linearity that are essential for this type of application. The only valid alternative with the same level of linearity is a simple shunt resistor. However, as the drive currents typically range from 5 to15A, power loss and temperature-induced drift can both affect the accuracy of the shunt resistor. The output from a shunt resistor also has some common-mode signals which are not present with a DC current transducer in which the primary and secondary signals are galvanically isolated. An ultra-high precision closed-loop DC current transducer would therefore be the preferred choice for this type of application.


Conclusion
Current transducers with the highest levels of accuracy, drift and response times were once used mainly by test laboratories. Now, with energy efficiency becoming a prime objective in virtually every market, the latest transducer technologies are extending the use of ultra-high precision transducers beyond high-end test and measurement applications and in the industrial and medical markets.


About the author
Stephane Rollier form LEM and Horst Bezold from Signaltech GmbH contributed this article.


To download the PDF version of this article, click here.


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