GxT Ferret 92 Color Labscope - Manual (Page 17)

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Voltage generators: Conventional O2 sensors operate in a range between 0 and 1 volt. AC generating sensors vary
in amplitude, but are usually under 10 volts.
The scope will display up to the selected Voltage Scale level. (10 Volt setting will display from 0 volts to 10 volts) In
most cases you’ll want to select a Voltage Scale slightly higher than expected voltage so the trace doesn’t range
off of the display. Voltage Scale may be adjusted once the trace is on the screen, as can other settings.
Time Base:
This setting will determine how much time is represented on the display. There are some things we need to consider
when selecting a Time Base.
First, we need to consider the duration of the event. How long does it take for the event we want to see to occur?
Suppose we want to look at a fuel injector at warm idle. An average pulse width should be around 3 mS. If we
wanted to see a lot of detail in the trace we’d use a relatively short Time Base, just slightly longer than the duration
of the event. If we want to leave room for change in pulse width, we’d use a longer Time Base.
Next, do we want to see the event repeated several times across the display? If so, a longer Time Base would be
necessary.
Last, do we want to see a single event or a chain of related events? If we want to see a chain of events we would
need some idea of the time required for it to take place.
Don’t be too concerned if your Time Base selection isn’t right the fi rst try. Like all settings, it can be adjusted once
you have the trace on the screen.
Trigger:
The Trigger setting will tell the scope when to begin drawing the trace. There are times when you’ll just want the
trace to scroll across the display. Maybe you’re monitoring a temperature sensor or something that has voltage
transitions slow enough to view in real time. Or maybe you’re testing a component that you are unfamiliar with and
want to look at the trace before setting a trigger. In either case you would select None. (no trigger)
Many events begin with a change in voltage. We’ll usually want to see an event from the beginning, so we would
select a voltage trigger. To trigger on increasing voltage we’d select a positive slope trigger. To trigger on decreasing
voltage we’d select a negative slope trigger.
There are also times when you’ll want to trigger on an external event. An external event is an event other than what
you want displayed. The fi ring of #1 spark plug is the most common event used as an external trigger and works
well for viewing anything that is related to camshaft or crankshaft rotation. Cam sensors, crank sensors, ignition
parade patterns and things of that sort would be good examples. This type of trigger will also sync the event to
the trigger source.
Trigger Level:
If we’ve selected a voltage trigger, whether positive or negative slope, we’ll need to set a Trigger Level. When a
positive slope trigger is selected, the scope will trigger when increasing voltage rises above the set level. With a
negative slope trigger, the scope will trigger when decreasing voltage falls below the set level.