CS201706B1 - Connection for determination of the exposition time - Google Patents

Description

The invention relates to a circuit for determining the exposure time for photographically scanning objects observed on a scanning electron microscope screen.

Taking a photographic image of the observed specimen is one of the basic operations of scanning electron microscopes. The image is obtained by photographic scanning from a scanning electron microscope screen.

The correct exposure is influenced by a number of factors, such as the brightness of the screen, the speed of scanning, the sensitivity of the photographic material, the aperture of the camera, etc.

Shooting is therefore performed at certain scanning speeds, at a constant aperture of the camera, which determines the exposure time. The brightness of the screen or the contrast of the displayed place remains as a variable.

You need to set the appropriate brightness of the screen to determine the exposure correctly. For this purpose, objective measurement of screen brightness must be ensured.

Scanning electron microscopes use different ways of measuring screen brightness. For example, the DC level of the screen modulation signal is measured to adjust the exposure value, or the screen grid or cathode voltage is measured directly. If a signal is applied to the screen grid and the brightness changes by changing the cathode potential, these methods cannot be used.

These prior disadvantages are eliminated by the wiring to determine the exposure time for photographic imaging of objects observed on the scanning electron microscope screen. The principle of the connection is that a compensating voltage source is connected to the cathode of the screen parallel to the DC voltage source via a divider consisting of two resistors, the center of the divider between the two resistors is connected to the inverting input of the differential amplifier. a capacitor and a resistor which are connected via a second terminal to a grounding conductor and a fourth resistor connected to a screen modulation electrode, while the output of the differential amplifier is coupled via a gauge adjustment circuit to a pointer meter.

The advantage of the circuit is the circuit simplicity with a minimum number of components, easy reproducibility during production and setting the exposure time, which is virtually independent of changing the DC level of the modulation voltage, or the change of the cathode potential.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated in more detail by the accompanying drawing, in which an example of connection is shown. The screen 1 is connected to the cathode 2 by a cathode DC voltage U1. The compensating voltage source 6 is connected in series via a divider of two resistors R1, R2 to the cathode of the screen 1. The modulation electrode to which the modulation voltage U ₂ is connected is connected via a fourth resistor R4 to a node with capacitor Ci by resistor R5 and a third resistor. R3, which is connected to the noninverting input of the differential amplifier 3. Its IEI inverting input is connected with the center divider between the first and second resistance R R _2nd The output of the differential amplifier 3 is connected via the meter adjustment circuit 4 to the pointer meter 5. The resulting voltage Ug is at the output of the differential amplifier 3.

The wiring works as follows during operation. The voltage Ui on the cathode of the screen 1 is applied through a divider consisting of the first and second resistors R1 and R ₂ to the differential amplifier 3 input. The compensating voltage source 6 connected in opposite polarity to the DC voltage source 2 ensures that the voltage at the

Claims (1)

Subject Connection for determining the exposure time for photographic imaging of objects observed on a scanning electron microscope screen, characterized in that it is connected to the cathode of the screen (1) parallel to the DC voltage source (2) via a divider consisting of two resistors (Ri, R ₂ ) a compensating voltage source (6), the center of the divider being coupled to the inverting differential input inverting the differential amplifier 3 approaching zero. The modulation voltage U ₂ is applied to the non-inverting input of the differential amplifier 3 via a low-frequency filter formed by the third and fourth resistors R ₃ , R ₄ and the capacitor Cp. E1 = _ Uj Uj U ₂ ' The desired transfer voltage is adjusted by selecting the resistance values Ri, R _2, R '5. Whenever the voltage U ₄ and U ₂ or both voltages simultaneously, the change of the output voltage _{U; j,} which recorded over circuit 4 to adjust .průběhu gauges include dial gauge 5. These changes are directly related to changes in screen brightness 1. It if change of the two voltages Ui and U ₂ are the same size and identical polarity does not change the brightness of the screen or to change the voltage U3, because the potential between the cathode and the modulation electrode is constant. The gauge adjustment circuit 4 adjusts the scale and at the same time protects the pointer 5 from overload. BACKGROUND OF THE INVENTION an amplifier (3) whose non-inverting input is coupled via a third resistor (R ₃ ) to a capacitor (Q) and a resistor (Ø ₅ ) connected to a ground conductor via a second terminal and a fourth resistor (R ₄ ) connected with the display modulation electrode (1), while the output of the differential amplifier (3) is coupled via the meter adjustment circuit (4) to the pointer meter (5). 1 drawing