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SECTION 2
OPERATION
2.1 INTRODUCTION
This section
contains
information
necessary
to set up the
Model 261 and operate
the unit. Also included
are compen-
sating
equations
necessary
when
using
the source
with
measuring
instruments
with higlh input voltage
drops.
2.2 FRONT
PANEL
CONTROLS
AND
TERMINALS
Figure 2-l shows the front panel of the Model 261, The func-
tions
of the various
controls
and terminals
are described
below.
POLARITY
Switch.
The POLARITY
switch
has four posi-
tions which
are used to control
power,
turn the instrument
output
off and on, and set the polarity
of the source output.
In the AC OFF position,
the IModel 261 power
is discon-
nected.
In the OFF position,
power is applied to the instru-
ment,
but the source is disconnected
from the output
jack.
When the POLARITY
switch
iri in this position,
the output
resistance
of the source
is equal to the reciprocal
of the
AMPERES
switch setting,
regwlless
of the multiplier
settings
in use. The + and - positions s,elect positive or negative cur-
rent output
values.
Range
(AMPERES)
Switch.
The range switch selects one
of eight decade current
ranges between
10~5 and 10.'*A. The
actual output
is affected
by the positions
of the three multi-
plier switches.
When the multiplier
switches
are in the 1 .OO
positions,
the range switch
indicates
the actual output
cur-
rent.
Multiplier
Switches.
The mull:iplier switches
control the in-
ternal voltage
source of the instrument.
These switches
pro-
vide multiplying
values that determine
the actual output
of
the source.
To determine
the current
output,
multiply
the
current range by the multiplier
s,etting. The multiplier
switch-
es control
the output
through
the use of a 3-decade
Kelvin-
Varley divider. The Xl and X.01 switches
each have 11 posi-
tions between
0 and 10; the X:1 switch
has 10 positions
be-
tween 0 and 9. The illuminated
decimal point between
Xl and
X.1 switches
also serves as a pilot lamp.
OUTPUT
Receptacle.
The
OUTPUT
receptacle
is a
Teflon@
insulated
UHF type connector.
The low (threaded)
side floats from ground
unless the COM and GND terminals
on the rear panel are connected
together.
A chassis ground
terminal
(GI is located next to the OUTPUT
connector.
2.3 REAR
PANEL
CONTROLS
AND TERMINALS
Figure 2-2 shows the rear panel of the source. The purpose of
the various controls
and terminals
is described
below.
Voltage
Switch.
The voltage
switch
sets the source for
105.125V
or 210.250V
operation.
A screwdriver
can be used
to set the switch to the desired position.
FUSE.
By unscrewing
the fuse holder cap, the fuse is ac-
cessable.
See Section 6 for fuse replacement
procedures.
Power
Cord. The 3wire
cord is permanently
attached
to the
rear panel. The opposite
end of the power cord has a stan-
dard 3-prong
plug attached.
This plug should
be used only
with grounded
outlets.
COM end GND terminals.
The COM terminal
is connected
to the low side of the source output.
The GND terminal
is
connected
to chassis ground,
which
is connected
to the
power line ground
wire in the 3.wire power cord. Normally,
the GND and COM terminals
are connected
together
with a
shorting
link, which
is provided.
The link can be removed
to
float the low side from ground.
2.4 PREPARATION
FOR USE
Before operating
the Model 261, perform the following
steps:
1. Set the line voltage
selection switch to the appropriate
set-
ting depending
on the local power line voltage.
Check to
see that the appropriate
fuse is installed.
CAUTION
Operating
the source
on en incorrect
line
voltage
may
damage
the
unit.
possibly
voiding
the warranty.
2. Sat the Model 261 front panel controls
as follows:
POLARITY
Switch:
AC OFF
Range Switch:
Desired current
range
Multiplier
Switches:
10.00
3. Plug in the source to AC power and rotate the POLARITY
switch
to the OFF position.
The decimal
point pilot light
should come on, indicating
the unit is receiving
power.
If
not, disconnect
the instrument
from the power
line and
check to see that the fuse is good.
2.5 BASIC
OPERATING
PROCEDURE
Operation
of the Model 261 is fairly straight
forward.
Once
the
unit
is connected
to the measuring
instrument,
the
operator
need only select the appropriate
range and multiplier
switch
settings
and select the output
current
polarity.
The
basic operating
procedure
is as follows:
1. Plug in the instrument
to the appropriate
power source and
rotate the POLARITY
switch to the OFF position.
The pilot
light should indicate
that power
is applied
to the source.
Allow
a one hour warm-up
period for rated accuracy.
2-1
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