Operating instructions

University of Saskatchewan
Electrical Engineering Laboratory Equipment Manual
 Normal
 Single
 TV
Auto level is the default triggering mode. It sets the trigger point to the 50% amplitude
point on the selected trigger source waveform. If there is no waveform present, a baseline is
displayed. Auto is a trigger mode that allows you to set the trigger threshold manually, but, like
the auto level mode, it will display a baseline if the trigger conditions are not met.
The normal trigger mode will display a signal only if a valid trigger signal exists that
satisfies all of the trigger conditions. If the trigger conditions are not met, the display will not be
updated.
The single trigger mode (single shot) triggers only once if the trigger conditions are met.
Once triggered, the oscilloscope automatically goes into the stop mode and must be rearmed
before it will reacquire data. The run button must be pressed to rearm the scope.
The holdoff knob is a very important control, as was stated earlier for the HP
54501A. When it is rotated, the trigger holdoff time is momentarily displayed at the
bottom left corner of the screen. Again, a general rule of thumb is to set the holdoff time
to be a little less than one period of the waveform you are examining if the scope is
having difficulty triggering.
The Slope / Coupling menu button brings up the following items:
 Slope rising/falling
 Coupling ac/dc
 Reject off/lf/hf (low frequency/high frequency)
 Noise reject off/on
The slope rise/fall item selects whether the scope should trigger off of a rising or
a falling edge that passes through the selected trigger threshold voltage on the trigger
source channel. The coupling selection allows you to choose whether the selected
input signal should be ac or dc coupled before it is passed to the trigger circuitry.
The reject/noise reject options are present to aid in triggering when examining
noisy waveforms. The LF reject option high pass filters the trigger signal with a cutoff
frequency of 50 kHz. The HF reject option will low pass filter the trigger signal, again
with a cutoff of 50 kHz. The Noise reject option simply decreases the trigger sensitivity
to help reduce the occurrence of false triggers caused by noise.