The following is a list of common controls found on the oscilloscope:
The power switch is used to turn the oscilloscope ON or OFF.
This control is used to locate the position of the trace if it is off the display. The BEAM FINDER button will indicate the approximate location of the trace. The position controls are then used to move the traceback on the display.
This is a reference voltage point used when compensating the probe. Most probes adjust points to produce a square wave signal of about 0.5 volts.
Intensity and Focus
The INTENSITY control adjusts the brightness of the trace. A bright spot should never be left on the display because it will burn a spot on the face of the cathode ray tube (CRT). This burned spot results in permanent damage to the CRT. The FOCUS control sharpens the image of the trace.
This is used to adjust the trace up or down on the display. If a dual-trace oscilloscope is being used, there will be two vertical POSITION controls. (A dual-trace oscilloscope contains two separate traces that can be used separately or together.)
CH 1–BOTH–CH 2
This control determines which channel of a dual-trace oscilloscope is to be used, or whether they are both to be used at the same time.
This control is active only when both traces are displayed at the same time.
The ADD adds the two waves together.
ALT stands for alternate. This alternates the sweep between Channel 1 and Channel 2.
The CHOP mode alternates several times during one sweep. This generally makes the display appear more stable. The CHOP mode is generally used when displaying two traces at the same time.
The AC is used to block any DC voltage when only the AC portion of the voltage is to be seen. For instance, assume an AC voltage of a few millivolts is riding on a DC voltage of several hundred volts. If the voltage range is set high enough so that 100 VDC can be seen on the display, the AC voltage cannot be seen. The AC section of this switch inserts a capacitor in series with the probe. The capacitor blocks the DC voltage and permits the AC voltage to pass. Because the 100 VDC has been blocked, the voltage range can be adjusted for millivolts per division, which will permit the AC signal to be seen.
The GND section of the switch stands for ground. This section grounds the input so the sweep can be adjusted for 0 volt at any position on the display. The ground switch grounds at the scope and does not ground the probe. This permits the ground switch to be used when the probe is connected to a live circuit. The DC section permits the oscilloscope to display all of the voltage, both AC and DC, connected to the probe.
This control adjusts the position of the trace from left to right.
This determines whether the time base will be triggered automatically or operated in a free-running mode. If this control is operated in the NORM setting, the trigger signal is taken from the line to which the probe is connected. The scope is generally operated with the trigger set in the AUTO position.
The LEVEL control determines the amplitude of the signal must be before the scope triggers.
The SLOPE permits selection as to whether the trace is triggered by a negative or positive waveform.
The INT. stands for internal. The scope is generally operated in this mode. In this setting, the trigger signal is provided by the scope. In the LINE mode, the trigger signal is provided from a sample of the line. The EXT or external, mode permits the trigger pulse to be applied from an external source.
Note: These are the major controls. Most oscilloscopes contain these controls.