Current Measurements; Resistance And Diode Measurements - Sperry instruments DM-350A Operating Instruction

are used to measure distorted waveforms such as
chopping, square of sawtooth waveform, a large amount
of measurement error will be introduced, thus making it
impossible to take accurate measurement of True RMS
values. The model DM-307A with True RMS capability
provides accurate measurement of True RMS values
regardless of the waveform. It also permits measurement
of AC only of AC plus DC coupled Current and voltage.
Here reference is made to the crest factor which is
defined to be the ratio of True RMS value to the peak
value as represented by the following formula:
Peak Value
Crest Factor =
True RMS Value
The crest Factor for model DM-370 is 3. This means that
a maximum voltage value to be measured is 3 times the
rated scale value of each range.
Sec. 8.2 CURRENT MEASUREMENTS
1. Insert the black and red test leads into the respective
"COM" and "mA" terminals.
2. Place the function switch to the 200mA position.
Always start with the highest range of the function to
be measured.
Do not attempt to take a current measurement if the
current is unknown or above 200mA. The "COM"
terminal potential should not exceed 500V measured to
ground.
3. Completely de-energize the circuit in which the
current is to be measured. Place the DMM in series
with the conductor carrying the current which is to be
measured. Energize the circuit.
Before changing ranges, always de-energize the circuit
completely. An open circuit exists between the test leads
during range change on the DMM.
CAUTION
CAUTION
The mA ranges are fuse protected. To avoid possible
electrical shock, instrument damage and/or equipment
damage do not:
1. Attempt to take mA current readings on circuits
having more than 200mA current flow.
2. Impress a voltage between the "COM" and "mA"
terminals exceeding 250Vac/dc. Some circuit
damage may result for voltages below 250Vac/dc.
3. Raise the "COM" terminal potential above 500V to
ground.
4. Energize the circuit. If the reading is within the next
lower range, switch to that range after completely de-
energizing the circuit under test. Continue changing
to lower ranges if the reading is within the next lowest
range to obtain the best accuracy.
5. Completely de-energize the circuit before removing
the test leads.
Sec. 8.3 RESISTANCE AND DIODE MEASUREMENTS
1. Insert the black and red test leads into the respective
"COM" and "V-Ω" terminals.
2. Place the range selector switch into the Ω range
desired for a measurement. (The test range
measures resistance from 000 up to 1999 and is
used to test the forward resistance value of diodes.
The diode check entails injecting a given current into
the diode juction to be tested and reading the voltage
drop across the diode. Models DM-350A, DM-370A
All resistance and diode measurements should be taken
on de-energized circuits only. To avoid possible
electrical shock, instrument damage and/or equipment
damage do not connect the "COM" and "V-Ω " terminals
to circuits having a potential difference exceeding
250Vdc/ac. Do not connect the "COM" terminal to
potentials exceeding 500V to ground.
3. Completely de-energize the circuit or device which is
CAUTION
CAUTION