Introduction to Vertical and Horizontal Deflection Factors for Oscilloscopes
(1) Vertical Deflection Factor Selection (VOLTS/DIV) and Fine Adjustment
The distance that the point of light is deflected on the screen under the action of a unit input signal is called the offset sensitivity, and this definition applies to both the X and Y axes. The reciprocal of the sensitivity is called the deflection factor. The unit of vertical sensitivity is cm/V, cm/mV or DIV/mV, DIV/V, and the unit of vertical deflection factor is V/cm, mV/cm or V/DIV, mV/DIV. In fact, due to the customary use and the convenience of measuring voltage readings, the deflection factor is sometimes used as the sensitivity.
Each channel of the oscilloscope has a vertical deflection factor selector switch. Generally, the band switch is divided into 10 steps from 5mV/DIV to 5V/DIV in 1, 2, and 5 steps. The value indicated by the band switch represents the voltage value of one vertical frame on the fluorescent screen. For example, when the band switch is set to 1V/DIV, if the signal dot on the screen moves by one frame, it represents a 1V change in the input signal voltage.
There is often a small knob on each band switch to fine tune the vertical deflection factor for each gear. Turn it clockwise to the end, in the "calibration" position, this time the vertical deflection factor value and the value indicated by the band switch. Turning this knob counterclockwise will fine-tune the vertical deflection factor. It should be noted that the fine adjustment of the vertical deflection factor may cause inconsistency with the value indicated by the band switch. Many oscilloscopes have a vertical expansion function that expands the vertical sensitivity by a factor of several (and reduces the deflection factor by a factor of several) when the trim knob is pulled out. For example, if the deflection factor indicated by the band switch is 1V/DIV, the vertical deflection factor is 0.2V/DIV when the ×5 expansion state is used.
When doing digital circuit experiments, the ratio of the vertical travelling distance of the measured signal on the screen to the vertical travelling distance of the +5V signal is often used to judge the voltage value of the measured signal.
(2) Time base selection (TIME/DIV) and trimming
Time base selection and trimming are used in a similar way to vertical deflection factor selection and trimming. The time base selection is also realised by a band switch, which divides the time base into several steps in the manner of 1, 2 and 5. The value indicated by the band switch represents the time it takes for the point of light to move one frame in the horizontal direction. For example, in 1μS/DIV, the point of light moving one frame on the screen represents a time value of 1μS.
The "Trim" knob is used for time base calibration and trimming. When the knob is rotated clockwise to the calibration position, the time base value displayed on the screen is the same as the nominal value indicated by the band switch. Turning the knob counterclockwise fine tunes the time base. The knob is pulled out in the scanning extension state. For example, in 2μS/DIV, the time value represented by one horizontal frame on the fluorescent screen in the scanning extended state is equal to For example, at 2μS/DIV, the time value represented by one horizontal frame on the fluorescent screen in the extended scan state is equal to 2μS×(1/10)=0.2μS.
T DS There are 10MHz, 1MHz, 500kHz and 100kHz clock signals on the bench, which are generated by quartz crystal oscillator and frequency divider with high accuracy and can be used to calibrate the time base of the oscilloscope.
The oscilloscope's standard signal source, CAL, is specially designed for calibrating the oscilloscope's time base and vertical deflection factor. For example, COS5041 oscilloscope standard signal source provides a square wave signal with VP-P=2V and f=1kHz.
The Position knob on the front panel of the oscilloscope adjusts the position of the signal waveform on the screen. Rotate the Horizontal Displacement knob (labelled with horizontal double arrows) to move the signal waveform left and right, and rotate the Vertical Displacement knob (labelled with vertical double arrows) to move the signal waveform up and down.
