Model 412A Sect.11 Page 1
SECTION II
OPERATING INSTRUCTIONS
2-1 LOW-LEVEL ELECTRICAL PHENOMENA Turn the 412A on and allow a few minutes
warm up.
Stray low-level electrical phenomena are present,
in one form or another, in nearlyall electrical cir-
cuits. The 412A does not distinguish between stray
and signal voltages; it measures net voltage. Thus, A. VOLTAGE MEASUREMENT
when using the lower voltage ranges, consider the
possibility of low-level electrical phenomena.
Thermocouples (thermoelectric effect), flexing of 1) Set FUNCTION selector to VOLTS.
coaxial cables (triboelectric effect), apparent re-
sidual charges on capacitors (dielectric absorp- 2) Set POLARITY switch to desired polarity.
tion), battery action of two terminals mounted on 3) Set RANGE switch to desired range.
an imperfect insulator (galvanic action) all can pro-
duce voltages within the range of the 412A. 4) Use VOLTS and COM leads to connect instru-
ment across circuit or component, and read voltage.
The 412A voltage probe, current/resistance lead,
and common lead are designed to have a very low B. CURRENT MEASUREMENT
thermoelectric effect with copper, the most com-
mon electrical conductor. However, you may en- 1) Set FUNCTION selector to MA.
counter other materials. For example, the leads
of many transistors are made of a mixtureof iron,
nickel, and cobalt known commercially as Kovar, 2) Set RANGE switch to desired range.
Fernico, etc. This material makes a very good
thermocouple with copper: about 40 1-1 v/OC with 3) De-energize circuit to be tested.
respect to a reference junction.
4) Use MA/OHMS and COM leads to connect in-
strument into circuit.
Whenever possible, connect the 412A leads to copper 5) Energize circuit, set POLARITY switch for up-
and maintain the points of connection at the same scale reading, and read current.
temperature, preferably ambient temperature.With
the leads so connected, any voltage indicated by
the 412A is developed within the circuit under test.
NOTE -
When measuring current, be sure there is no con-
nection between the chassis-ground and cabinet-
2-2 OPERATING INSTRU CTI ONS ground terminals of the DC AMPLIFIER OUTPUT
connector. --------------
CAUTION
Do not overload the instrument. Amplifier input,
current shunts, and internal resistance standards C. RESISTANCE MEASUREMENT
are not protected from extreme overload. Momen- 1) Set FUNCTION selector to OHMS.
tary overloads ten times full scale will notdamage
the instrument. ---- ---------- 2) De-energize circuit to be measured. |
ACEC
