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Low Current Source LCS-02

INTRODUCTION
Ultra-Low Constant Current Sources are needed when the sample resistance, either inherently or due to contact resistances, is large. These include the resistivity measurement of silicon wafers or high resistivity film deposits. Large values of the sample resistance make the measurement prone to noise pick-up from the mains and elsewhere. This is one of the most significant problems of high resistance measurement.
In the present unit the problem of pick-up has been reduced to very low levels by having a battery operated source. Since the current requirement is small and the circuit being specially designed for this purpose, the batteries should have a reasonably long life. Further, a transistor circuit has been preferred over an Op-Amp based circuit as it offers a reduction of the battery count and is also simpler. An internal voltage reference of 2.5 volt ensures reliable operation even when the batter voltage falls and a ten turn potentiometer makes the current adjustment very easy. The actual current is read on a 31⁄2 digit LCD display. There are two current ranges which may be selected with the help of a switch the panel.

Description

Ultra-Low Constant Current Sources are needed when the sample resistance, either inherently or due to contact resistances, is large. These include the resistivity measurement of silicon wafers or high resistivity film deposits. Large values of the sample resistance make the measurement prone to noise pick-up from the mains and elsewhere. This is one of the most significant problems of high resistance measurement.

SPECIFICATION
Open Circuit Voltage : 15V
Current Range : 0-2μA, 0-20μA, 0-200μA, 0-2mA
Minimum : 1nA at 0-2μA range
Accuracy : ± 0.25% of the reading ± 1 digit
Display : 31⁄2 digit, 7 segment LCD with autopolarity and decimal

indication

Load Regulation : 0.05% for 0 to full load
Power : 3 x 9V batteries

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