| 摘要 |
PURPOSE:To facilitate easy reading of the indicated value by using an n channel field effect transistor to extend the indication of a point near the limit of the lifetime and therefore having the equally divided scales of indication to the overall gap depth of a magnetic head. CONSTITUTION:The indication value of an indicator 31 such as a meter, etc. is extended by using an n channel field effect transistor 29. This is due to a fact that the variation of an output current ID,S, i.e., the current flowing to the indicator 31 is large although the variation of voltage of a point (c) near zero of the gap depth D of a head 25 to be measured, i.e., the variation of the input voltage VGS of the transistor 29 is small. Thus the indication is improved at a point near discrimination for the lifetime of the head 25. At the same time, the indication scales can be equally divided for display to the indicator 31 to the whole depth D1-D2 of the head 25. This facilitates easy reading of the indication value of the indicator 31.
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