Control for electron microprobe

Claim 1

In an electron microprobe apparatus for use with a source of power for analyzing a sample mounted on a movable holder by producing a secondary emission of X-rays from the sample by impacting an electron beam thereupon and for use with computer means for producing actuating signals and control signals and having an informational input, wherein the apparatus includes a cathode device for producing said electron beam, an X-axis beam control device between the cathode device and the sample for controlling the orientation of the beam along an X-axis transverse thereto, a Y-axis beam control device between the cathode device and the sample for controlling the orientation of the beam along a Y-axis transverse thereto, an X-axis holder control device for controlling the position of the holder along a first axis transverse to the beam, a Y-axis holder control device for controlling the position of the holder along a second axis transverse to the beam, an X-ray detector, and an adjustable device for picking up the secondary emission and separating it into components and directing selected components to said detector, the combination therewith of: a plurality of power driven means connected to said devices for controlling the setting of the respective devices and for producing electrical feedback signals in analogue form representative of the control settings of the devices; control matrix means connected between the computer means and the power driven means for directing actuating signals from the computer means to the respective power driven means as dictated by control signals from the computer means; an analogue to digital converter having an analogue input and a digital output, said digital output being connected to said informational input of the computer means; selector matrix means connected to said power driven means for receiving said feedback signals, to said computer means for receiving control signals and to the input of said converter for selecting a feedback signal as dictated by a control signal from the computer means and delivering said selected signal to said converter so that said selected signal is delivered to said computer means by said converter in digital form, said matrix means comprising a plurality of switches each having an operating element, a plurality of electric circuits, each circuit connecting a respective switch and a respective device to the source of power, said switches being controllable between a first state at which each switch energizes the respective device through the respective electric circuit and a second state at which said respective device is deenergized, and means operatively connecting said each of said switches to said computer means to actuate the operating element of a respective switch as dictated by a control signal from the computer means; a beam control device connected to said cathode device for controlling the emission of electrons from the cathode device and one of said power driven means connected to said emission control device to control said emission; and a sample current measuring device for producing an output signal indicative of the current flow from the sample to ground, said current measuring device being connected to said selector matrix means; said X-ray detector including a ratemeter and a scaler each producing output signals, said ratemeter being connected to said selector matrix means to deliver its output signal thereto, said ratemeter being connected to said computer means to deliver its output signal thereto; each of the X-axis holder control device and the Y-axis holder control device including a rotatable threaded shaft which rotates a given number of turns to traverse the holder through its maximum range of movement; and each of the power driven means connected to said holder control devices comprising: an electric motor connected to the control matrix means to be operated in accordance with signals from the control matrix, means operatively connecting said motor to said shaft for driving the shaft in accordance with the operation of the motor, a first potentiometer having a contact movable within a given range on the potentiometer, said contact being connected to said selector matrix means, means operatively connecting said movable contact and said shaft for moving the movable contact within said range on said potentiometer in response to said shaft rotating said given number of turns, second potentiometer means having contact means movable repetitively through a given range on the second potentiometer, said contact means being connected to said selector matrix means, gearing means operatively connecting said movable contact means of the second potentiometer means and said shaft for moving said contact means through a greater portion of its range in response to a given rotation of the shaft when the portion of the range of the first potentiometer traversed by the contact thereof in response to the same given rotation of the shaft, and means connecting said potentiometer and potentiometer means to said source of power for imposing a voltage across the potentiometer and the potentiometer means, whereby voltages are obtained at said contact and said contact means which together are indicative of the holder position along the respective axis.