1.
SECTION I
GENERAL DESCRIPTION
1-1. GENERAL
.
1-2. TheModel 412A
/
AR DC Vacuum Tube Voltmeter is a precision, wide range, multipurpose instrument
which covers the entire range of dc voltage, current, and resistance measurements normally encountered
in electronic equipment.
1-3. It measures
de
voltages over the wide range of 0.02 millivolts to 1000 volts on thirteen ranges ar-
ranged in al, 3, 10 sequence from 1 mv full scale to 1000 v full scale. Overall accuracy on all thirteen
ranges Iswíthín ±1
%
of full scale. Voltage differences can be measured easily since the input circuit is
í
so-
lated from the case and from the power line ground.
1-4. DAMAGE IN SHIPMENT.
1-5. Inspect and operate this instrument upon receipt. Section
'
I'V includes a performance check which
is a good test as part of incoming quality control inspection. The check can be made with the instrument
in its cabinet
.
If there is any damage, see the
"Claírn
for Damage in Shipment" paragraph at the back of this
manual.
1-6. POWER CABLE.
1-7. The three-conductor power cable supplied with this instrument terminates in a polarized three-prong
male connector recommended by the National Electrical Manufacturers' Association. The third contact
is an offset round pin added to a standard two-blade connector. This contact grounds the instrument when
used with an appropriate receptacle. An adapter should be used to connect the NEMA plug to a standard two-
contact output
.
When the adapter is used, the ground connection be comes a short lead from the adapter.
This lead should be connected to a suitable ground for the protection of operating personnel
.
1-8. 115-230 VOLT OPERATION.
1-9. A switch located on the instrument rear converts the Model 412A
/
AR for use from either a 115-volt or
230-volt, 50-60 cps power source. The switch changes the connection of the dual 115-volt primary windings
of the power transformer from a parallel combination to a series combination, or vice versa. Switch positions
are marked 115 and 230.
1-10. To convert the instrument from 115-volt operation to 230-volt operation, or vice versa, insert a
screwdri ver
blade
into the switch slot and slide the slot until the marking indicates the line voltage.
At the time of the change, replace the line fuse. A
O.
6 ampere slow-blow fuse should be used for 115-volt
operation; a 0.4 ampere slow-blow fuse should be used for 230-volt operation.
CAUTION
Be sure the 115/230 V switch is set at the proper position before applying power to the instrument
Incorrect setting of the switch can result in damage to the instrument.