Specifications

50


=






You can calculate the scope's rise time 

in ns from:


=
350

where B is the scope's bandwidth in MHz.
Probe compensation
Probe compensation is the process of matching the probe's electrical characteristics to the scope's.
The result is that signals viewed by the scope using the probe will be accurately depicted (excluding the
roll-off due to the probe's bandwidth).
Probe compensation is usually done with a square wave signal provided on the scope's front panel.
This is usually a 1 to 2 Vpp square wave at 1 kHz (and, hence, the compensation is termed low-
frequency compensation). The user hooks the probe to the scope and connects the probe's center
conductor to the square wave. A non-conductive screwdriver is used to adjust a small capacitor on the
probe so that the waveform on the screen matches a square wave signal with no undershoot or
overshoot.
The key take-away about probe compensation is that a poorly-compensated probe exposes you to
measurement errors -- and you won't know you're making an error unless you check for it.
A probe's compensation should be checked when it is first connected to the scope. If you've used that
probe with the scope's different channels and know the compensation is good for all the channels, then
you might relax that requirement if you know no one else has used the probe. Even so, it's probably
good practice to check your probe compensation at the start of every day. If the probe might have been
used with another scope,
always check the compensation.
Probe types
Many different scope probes are available. Passive probes are the biggest sellers because they are
lower cost and more robust. Probably the most common probe is the 10X probe with the bandwidth the
user needs. 1X/10X probes are also popular, as they contain a switch in the probe body that lets you
switch between the 1X position, 10X position, and a position where the input line is connected to the
ground line. However, a disadvantage of a 1X/10X probe is that you can accidentally leave it in the 1X
position when you need it to be in the 10X position. This can result in qualitative and quantitative
measurement errors because the attenuation is not what you expect and the frequency response is
substantially different than in the 10X position.
100X and 1000X passive probes are also available. These can be useful because they reduce the
capacitive effects even more, but at the cost of more signal attenuation. They are often made to
withstand voltages into the kilovolt ranges. For example, the Cal Test GE3225 100X probe has a 200
MHz bandwidth, 5 pF of capacitance, and a 2 kV CAT I voltage rating.
Active probes are used for differential measurements and probes with high frequency response with
minimal circuit loading.
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