Oscilloscope

TRACE INTENSITY

The trace intensity control is located to the right hand side of the display. It adjusts how bright the trace will be. Turn the knob in a clockwise direction and the brightness is increased, turn the knob anti-clockwise for reduction in intensity.

TRACE FOCUS

This control is located above the intensity control, and adjusts the clarity of the trace on the display. Turn the control to the left to reduce clarity, and turn the control to the left to increase clarity.

TRACE VERTICAL CENTER ADJUST

There's two controls (one for each input channel) located above the volts/div control for their respective channels. To move trace towards the bottom of the screen, turn knob to the left. Turn knob to the right to move the trace towards the top.

HORIZONTAL TRACE ADJUST

Located to the right of the time base control, this control is simply used to adjust the trace to the right side on the display, or to the left side on the display. By turning the knob in a clockwise direction the trace will move towards the right, and counter clockwise to adjust the trace towards the left.

TRIGGER SOURCES

Trigger sources are grouped into two categories. The first is when the signal is an internal signal, and the second type is when the signal is an external signal. The trigger circuit operates the same whether it's an external or an internal triggering source. The switches 'source' and 'int' determine the trigger source. When the source switch is switched over to 'int' the internal triggering sources are turned on. When on 'norm' and the signal is applied the sweep is then activated. When there's no signal, the base line trace will disappear The P-P Auto-TV Line mode is needed for a waveform with a repetition rate of at least 20Hz, the scope will then trigger off this waveform. When the signal is lower than 20Hz the 'Sweep free' mode is activated. The range of the trigger level is determined by the peak-to-peak range of the trigger signal. The TV Field can be activated when both the P-P Auto and Norm buttons are pushed. This allows triggering on television field signal. By pressing the spring-return button marked 'SGL SWP RESET' the scope will then be armed for a single-sweep display. For each signal that is triggered, only one sweep will be displayed. By pressing the 'SGL SWP RESET' again, another sweep will be displayed on the screen. This control is very useful for signals, which cause unstable displays, or signals that are non-repetitive.

TIME BASE SELECTIONS
 
 

The oscilloscope has a time base usually referred to as the main time base and it is probably the most helpful. A lot of the oscilloscopes have 'delayed time base', a time base sweep that begins only after a pre-determined time from the start of the main time base sweep. The delayed time base requires the setting of a delay time, and possibly the use of delayed trigger modes.

TRIGGER CONTROLS

The trigger controls let you stabilize repeating waveforms and capture single-shot waveforms. The trigger makes repeating waveforms appear static on the oscilloscope display. Imagine the jumble on the screen that would result if each sweep started at a different place on the signal.

TRIGGER LEVEL AND SLOPE

For edge triggering, the trigger level and slope controls provide the basic trigger point. You select the slope and voltage level that you want to trigger at. When the trigger signal matches your settings, the oscilloscope generates a trigger. The slope control determines whether the trigger point is on the rising or the falling edge of a signal. A rising edge is a positive slope and a falling edge is a negative slope. The level control determines where on the edge the trigger point occurs.

TRIGGER MODES

The trigger mode determines whether or not to draw a waveform, if the oscilloscope does not detect a trigger. Common trigger modes include normal and auto. In normal mode the oscilloscope only sweeps if the input signal reaches the set trigger point; otherwise (on an analog oscilloscope) the screen is blank. Normal mode can be annoying, since you may not see the signal at first, if the level control is not adjusted correctly. Auto mode causes the oscilloscope to sweep, even without a trigger. If no signal is present, a timer in the oscilloscope triggers the sweep. This ensures that the display will not disappear if the signal drops to small voltages. It is also the best mode to use if you are looking at many signals and do not want to bother setting the trigger each time. In our lab, you will probably use both modes: normal mode because it is more flexible, and auto mode because it requires less alteration. Some oscilloscopes also include special modes for single sweeps, triggering on video signals, or automatically setting the trigger level.

TRIGGER COUPLING

as you can select either AC or DC coupling for the vertical system, you can choose the kind of coupling for the trigger signal. Besides AC and DC coupling, your oscilloscope may also have high frequency rejection, low frequency rejection, and noise rejection trigger coupling. These special settings are useful for eliminating noise from the trigger signal to prevent incorrect triggering.

TRIGGER HOLDOFF

Sometimes getting an oscilloscope to trigger on the correct part of a signal requires great skill. Many oscilloscopes have special features to make this task easier. Trigger holdoff is an adjustable period of time during which the oscilloscope cannot trigger. This feature is useful when you are triggering on complex waveform shapes, so that the oscilloscope only triggers on the first trigger point it sees.

We hope that you have enough knowledge now to complete the lab and then answer the questions. Good luck.