Simpson 270 Series - Page 36

Operation
4.10 AC VOLTAGE MEASUREMENT
0-2.5 THROUGH 0-500V RANGE
| WARNING |
Branch and distribution circuits (120/240/480V etc.)
can deliver dangerous explosive power momentarily into
a short circuit before the fuse/breaker opens the circuit.
Make absolutely certain that the Instrument switches
are set correctly, jacks properly connected, and that the
circuit power is turned off before making connections
to such circuits.
4.10.1 The 270 responds to the average value of an AC waveform.
The Dial is calibrated in terms of the rms value of a pure sine wave.
If the waveform is nonsinusoidal, and depending upon its wave-
form, the reading may be either higher or lower than the true rms
value of the measured voltage. Thus an error may be introduced
if the 270 is used to measure a nonsinusoidal waveform. Also,
accuracy is lessened at higher input frequencies (Figure 4-2).
4.10.2 Before proceeding with the following steps, review the
Safety Precautions in Paragraph 4.2.
a. Set the function switch at AC (Figure 4-3).
b. Set the range switch at one of the five voltage range positions
marked 2.5У, 10У, 50У, 250V or 500У.
NOTE: When іп doubt as to actual voltage present, al-
ways use the highest voltage range as a protec-
tion to the Instrument. If the voltage is within a
lower range, the switch may be set for the lower
range to obtain a more accurate reading.
c. Plug the black test lead into the - COMMON jack and the red
test lead into the + jack.
4-10