Philips 6652C - Time Measurements Using Probes

SLOPE*
This button inverts the EXT CONTR input making
the function se lected with the ARMING / AVG /E XT
GATE / OFF-switch active on the opposite slope .
The selection is indicated on the front panel.
* Not available on the PM 6652,-54.
Channel Co nsiderations
Input 8 is limited to 10MHz in the RATIO modes.
Input C may accept frequencies as low as
(approxi mately ) 80MHz.
TIME M EA SUREMENTS USING PROBES
· Introduction
It is possible to calibrate the probes for
Time / Phase measurements directly with a PM 6652
or PM 6654 Timer/Counter. The compensation pro-
cedure requires, besides the counter, a genera-
tor capable of delivering a 500 Hz square-wave
signal with 20 Ypp amplitude.
Why are probes used at all?
a) Probes are used to reduce the influence of
the measuring instrument on the device under
test. When measuring in high-impedance sy-
stems, an 1 Mohm load (normal counter input)
might be too low and a 10 Mohm load (probe)
is required.
b) Probes are sometimes used to reduce high vol-
tage levels. The measured level is divided by
10 usi ng a 10 Mohm/1 Mohm probe.
c) A probe is easy to hook on to different
measuring points in a test object. For this
purpose however it is not necessary to u se a
10:1 probe. A single wire with a test hook
might do
as well ( hsimple 1:1 probeh).
Measurement problems
a)
When an over-compensated probe is used in
pulse measurements, an "overshoot" is
generated in the counters input. This makes
the Vpp measurement go wrong . The display
shows a too high value.
~ 8
0
b) Very short Time Interval measurements might
go
wrong when two differently compensated
probes are used. An example is given below:
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