Fluke 787 - Manual (Page 26)

787
Users Manual
18
Measuring Electrical Parameters
The proper sequence for taking measurements is as
follows:
1. Plug the test leads into the appropriate jacks.
2. Set the rotary knob.
3. Touch the probes to the test points.
Input Impedance
For the voltage measurement functions, input impedance
is 10 M
Ω . See the specifications for more information.
Ranges
A measurement range determines the highest value the
Meter can measure. Most meter measurement functions
have more than one range (see the Specifications).
Being in the right range is important:
• If the range is too low, the display shows OL
(overload).
• If the range is too high, the Meter will not be
displaying its most accurate measurement.
The Meter normally automatically selects the lowest range
that will measure the applied input signal (Auto showing
on the display). Press Kif you want to lock the
range. Each time you press K, the Meter selects the
next higher range.
If you have locked the range, the Meter resumes auto
ranging when you change to another measurement
function or you press K and hold it for 1 second.
Measuring a Composite Signal
Because the input is dc-coupled, to measure an ac
voltage or frequency with a dc bias, you must manually
select the range specified in Table 7. For example, to
measure 100 mV ac with 20 V dc superimposed, select
the 4 V range.
Table 7. Range Requirements for Measuring a
Composite Signal
Range (ac) Max. Allowable AC + DC
400.0 mV 3 V
4.000 V 30 V
40.00 V 300 V
400.0 V 400 V
1000 V 1000 V