Fluke 341A - Current Limit; Operation; Overload Protection; Mechanical Zero Adjustment

341
A
the
Mode! 341A/343A is
equipped with
remote sensing,
which maintains
regulation at
the load
independent of
lead
length.
343A
Set
the
FUNCTION
switch to STANDBY/RESET
and remove the
short from across the OUTPUT ter-
minals.
2-17.
Remote
Sensing.
If the
voltage developed in the
load connecting
leads is found
to be excessive, proceed as
follows:
a.
With the FUNCTION
switch set to OFF or to
STANDBY/RESET,
remove the front-panel shorting
links between
the
SENSE
and OUTPUT
terminals.
b.
Using
a
twisted
pair
of
insulated wires, connect the
+ SENSE terminal to
the positive side of the load,
and connect the
-
SENSE
terminal to the
negative
side of the load.
CAUTION!
Ensure that the SENSE
terminals are connected
to
the load in
the proper
polarity. Incorrect
connections
will result in
loss of
regulation and
possible damage to
the
instrument. When re-
mote sensing is
not used, the
SENSE
terminals
must be
connected
to
the OUTPUT
terminals
with the
front-panel shorting
links.
2-18. CURRENT LIMIT
OPERATION
2-19.
The CURRENT
LIMIT control
sets the operating
point of the
controlled
current limiter, which limits
the
instrument
output current to any
value between 1 and
25
milliamps. The approximate
value of limiting
current is
indicated
by a
1 to
25 scale
circumscribed about the
CURRENT LIMIT control
on the front panel.
If no cur-
rent limiting is
desired, set the
CURRENT LIMIT control
fully
clockwise
(25).
In
this position,
maximum
instru-
ment
output current is available
at
all
voltage settings.
If
some degree of current limiting is
desired,
proceed
as
fol-
lows:
2-20. OVERLOAD PROTECTION
2-21.
The Model 341A/343A is
automatically protected
against
current overload, and a continuous short circuit will
in no
way harm the unit. At
output voltage
dial settings of
299.99X (299.999Xon the Model 343
A)
or less, the output
voltage will return quickly upon
removal
of the overload.
At voltage dial settings of 300.000 (300.0000 on the Mod-
el
343A)
and above,
a
short circuit at the output will trip
the instrument to STANDBY. Trip is evidenced
by
illu-
mination of the
CURRENT LIMIT
lamp and extinction of
the ON lamp. After the overload condition is
corrected,
the instrument may be reset by setting the FUNCTION
switch to the STANDBY/RESET position
momentarily
and then back to ON.
2-22. Output voltages are fully controlled when down-
ranging or switching
to STANDBY.
This is
accomplished
by
a pair of crowbar relays, which discharge the high vol-
tage filter
capacitors
in a
series of steps.
The action of the
crowbar relays is very rapid and is audible to the user.
When
downranging from
the
1000
volt
range
(500
to
1000 volt dial settings)
to
the 100 or 10 volt ranges, crow-
bar
operation
can be heard as a
rattle
as
the
switch position
is changed.
The crowbar
circuit provides continuous
pro-
tection as long as downranging is not excessive; however,
if
downranging occurs consistently at intervals less than
5 seconds, the
instrument
will automatically trip to
STANDBY.
2-23. MECHANICAL ZERO
ADJUSTMENT
2-24.
When necessary, mechanically
zero the
meter
with
the adjustment
screw
on
the front panel. If
the
instrument
has been
operating, it
must be
turned
off for at least 3
minutes prior
to
this
adjustment.
a.
Set
the Model 341A/343A control as
follows:
2-25. OPERATION AS A VOL I
AGE CALI-
BRATOR
FUNCTION
RANGE
Voltage dials
CURRENT LIMIT
STANDBY/RESET
10
1.00000
(Model 341 A)
1.000000
(Model
343A)
Fully clockwise
b. Place a short across the
+
and
-
OUTPUT terminals.
2-26.
To use
the Model 341A/343A as a
voltage source,
proceed as follows:
a. Set the FUNCTION
switch
to STANDBY/RESET.
Allow at least
a
10-minute
warm-up period if the
instrument
has
just been
energized.
c.
Set the FUNCTION switch to METER
CURRENT.
d. Set the output current limit
by
rotating
the
CUR-
RENT LIMIT control
counterclockwise
until
the
panel meter indicates the desired limiting current.
Connect
the SENSE
terminals to
the
OUTPUT
ter-
minals
with
the shorting
links provided and.
connect
the
load. If remote sensing is
desired, connect the
SENSE terminals to
the load
as
described in para-
graph
2-17.
2-5