Heathkit IM-18 User Manual

Page 24
TEST AND CALIBRATION
During
the
preparation
of
the
test
leads
and
cabi-
net,
the
VTVM
has
had
an
opportunity
to
warm
up
thoroughly
and
should
now
be
calibrated,
Turn
the
instrument
off
and
make
sure
that
the
mechanical
zero
position
of
the
meter
pointer
is
correct,
If
not,
adjust
as
before,
(J Turn the instrument on again,
ZERO ADJUST
() Set the Function switch to DC+, Check oper-
ation of the ZERO ADJ control, Turning
this control should move the meter pointer
part way up scale, Set the pointer to zero at
the left side of the scale and check for
zero positioning when the Function switch
is changed to DC-, It should be possible to
obtain a ZERO ADJ control position that will
permit the meter pointer to remain station-
ary when switching through from DC+ to
DC-, If there is an appreciable zero shift
of more than two divisions on the scale,
it should be regarded merely as an indi-
cation that additional aging of the 12AU7
tube is required, This aging canbe obtained
by leaving the instrument turned on for a
period of 46 hours or more, or through con-
tinued use of the VTVM with periodic cali-
bration,
DC CALIBRATE
(-
)
Insert
the
test
lead
phone
plug,
Set
the
Function
switch
to
DC+,
the
Range
switch
to
1.5
V
and
the
probe
to
DC,
Connect
the
probe
to
lug
1
on
the
rear
wafer
of
the
Range
switch
(the
point
to
which
the
blue
ca-
ble
wire
is
connected
in
Pictorial
4).
(, ) Adjust the DC Calibrate control so that the
meter pointer falls directly over the very
small red dot on the meter face, Approach
the red dot going up scale by turning the
screwdriver control and watch the meter
read 1,4 volts, and 1,5 volts, and then the
red dot, As soon as the red dot is reached,
stop turning the DC Calibrate control, Re-
member that the Range switch must be set
on 1.5 V for this adjustment,
OHMS CHECK
{ ) Set the Function switch to OHMS, Set the
OHMS ADJ control for full seale (infinity).
Set the probe switch to AC-OHMS (the posi-
tion opposite the DC marking) and touchthe
probe to the common test clip, The meter
pointer should drop to zero at the left end
of scale (no resistance),
AC CALIBRATE
NOTE: Your AC power line outlets may be
either 2-wire or 3-wire types, Determine which
type you have and complete the appropriate AC
Calibration instructions, Use the AC Calibrate
With Line Cord Adapter for the 2-wire outlets
and AC Calibrate Without Line Cord Adapter for
the 3-wire outlets,
AC Calibrate With Line Cord Adapter
CAUTION: Do not allow the green wire on the line cord
adapter to be grounded in any way. or to touch any part of
the VTVM. A good way to prevent this is to put a piece of
tape over the spade lug on the end of Lhe green wire.
( ) Install the line cord adapter on the line
cord,
{ ) Temporarily remove the phone plug from the
jack,
{ ) Set the Range switch to 1.5 V andthe Func-
tion switch to AC,
{ ) Adjust the AC Balance control so no move-
ment is detected when switching from AC
through DC- to DC+,
{ ) Set the Range switch to the 150 V range if
you wired your VTVM for 120 VAC opera-
tion, or to the 500 V range if you wired the
VTVM for 240 VAC operation,
Set the Function switch to AC,
Set the AC Calibrate control fully clockwise,
Set the switch on the test probe to AC,
)
)
) Reinsert the phone plug,
)
)
Connect the test probe to one side of the AC
line and then the other side, Note the lowest
reading and remove the probe from the AC
line,

Heathkit IM-18 Specifications

General

Brand	Heathkit
Model	IM-18
Category	Measuring Instruments
Language	English