21
3.11 Direct Current Measurement
Do not change the range setting of the range or function switches while the circuit
is energized.
Never disconnect test leads from the circuit under measurement while it is ener-
gized.
Always turn the power off and discharge all the capacitors before changing switch
settings or disconnecting leads.
Never exceed the circuit-to-ground voltage of the instrument (1000 V max., Table
1-1, item 16).
Always connect the instrument in series with the ground side of the circuit.
In all direct current measurements, make certain that the power to the circuit being
tested has been turned off before connecting and disconnecting test leads or
restoring circuit continuity.
3.11.1
Direct Current Measurement 0-50
μ
A Range
a.
Set the function switch at +DC.
b.
Plug the black test lead into the -COMMON jack and the red test lead into the
+50
μ
AMPS/250mV jack.
c.
Set the range switch at 50
μ
AMPS (dual position with 50V).
d.
Open the ground side of the circuit in which the current is being measured.
Connect the VOM in series with the circuit. Connect the red test lead to the
positive side and the black test lead to the negative side.
e.
Read the current on the black DC scale. Use the 0-50 figures to read directly
in microamperes.
NOTE:
For polarity reversing see paragraph 3.4.
3.11.2
Direct Current Measurement 0-1mA Through
0-500mA Range
a.
Set the function switch at +DC.
b.
Plug the black test lead into the -COMMON jack and the red test lead into the
+jack.
c.
Set the range switch at one of the four range positions marked 1 mA, 10 mA,
100 mA or 500 mA.
d.
Open the grounded side of the circuit in which the current is being measured.
Connect the VOM in series with the circuit. Connect the red test lead to the
positive side and the black test lead to the negative side.
e.
Turn the power on. Read the current in milliamperes on the black DC scale.
For the 1 mA range, use the 0-10 figures and divide by 10. For the 10 mA
range, use the 0-10 figures directly. For the 100 mA range, use the 0-10
figures and multiply by 10. For the 500 mA range, use the 0-50 figures and
multiply by 10.
!
NOTE:
The maximum voltage ratio that can be measured is +50 dB on the 0-250V
range.
d.
If dB measurements are being made to a 0.006 watt into 500 reference
level, su7 dB from the reading obtained on the 260.