HP 740B Operating And Service Manual page 18

r
,
Model 740B
- - - - - N O T E - - - -
Either local or remote sensing
must be used at all times in
Standard mode.
3 -24. GUARDING.
3 -2 5. The output cable GUARD terminal is connected
to the Model 740B guard chassis and may be used to
reference the guard chassis to a desired potential.
Normally the GUARD terminal is connected to the
- OUTPUT terminal using the strap attached to the
GUARD terminal. The GUARD terminal may, however,
be connected to a reference potential or guard terminal
in the load to reduce the effects of unequal ground
potentials, stray ac pickup, etc.
3-26. NEGATIVE OUTPUTS.
3-27. FLOATING.
3-28. Negative output voltage not referenced to earth
ground is obtained by connecting the + OUTPUT and
+
SENSE terminals to the high (least negative) side of
the load and connecting - OUTPUT and - SENSE to
the low (most negative) side of the load. The INPUT
and OUTPUT
..Jo
terminals must not be connected to
any of the other terminals.
3-29. GROUNDED.
3 -30. Negative outputs referenced to earth ground are
obtained by connecting the + OUTPUT and + SENSE
leads to the ground reference point in the circuit under
test. The 740B then drives the - OUTPUT and - SENSE
leads negative with respect to the ground reference.
Again, the INPUT and OUTPUT
..Jo
terminals must
not be connected to any of the other terminals.
~
DO NOT FLOAT - OUTPUT
TERMINAL MORE THAN
500 V ABOVE OR BELOW
EARTH GROUND (~ ).
3-31. USING THE ZERO CONTROL.
3 -32. In Standard mode, the ZERO control sets the
output voltage zero reference. The ZERO control
range of adjustment varies with the voltage range
selected (Table 3-2).
Table 3-2. ZERO Control Range
Model 740B
ZERO Control,
Voltage Range
Approximate Range
of Adjustment
1 V ± 10 }J.V
10 V ± 100 }J.V
100 V
±
1mV
1000 V ± 10 mV
01794-1
Section III
3-33. The ZERO control may beused to set the output
to exactly zero volts or to null the effects of small dc
offset voltages existing in a test setup. Offset voltage
is present if the load (divider, potentiometer, etc.)
produces a small voltage with no apparent drive volt-
age applied. Such voltages are usually produced when
contact is made between dissimilar metals, tempera-
ture gradients exist in a test setup, etc.
3-34. SETTING THE OUTPUT TO ZERO.
3-35. To set the output voltage zero reference to 0 V,
proceed as follows:
a. Set 740B FUNCTION to STD, RANGE to the
desired range , VOLTAGE SET and STANDARD
VERNIER to zero and OUTPUI on.
b. Connect a sensitive dc null detector across
the + and - OUTPUT terminals.
c. Set null detector range to obtain an off-null
indication.
d. Set 740B ZERO control to obtain a null indi-
cation.
e. Disconnect null detector.
- - - : : - - - NOTE - - - - -
The ZERO control setting varies
slightly f rom range to range. Re-
adjust ZERO control each time
RANGE is changed.
3-36. NULLING EXTERNAL OFFSETS.
3 -37. To null the effects of external dc offset voltage;
proceed as follows:
a. Set 740B FUNCTION to STD, RANGE to the
desired range, VOLTAGE SET and STANDARD
VERNIER to zero and OUTPUT on.
b. Connect the OUTPUT terminals to the load.
c. Connect a sensitive null detector across the
load (or across the reference leg of the load).
d. Set null detector range to obtain an off -null
indication.
e. Set 740B ZERO control to obtain a nullindi-
cation.
- - - - - N O T E - - - - -
The ZERO control setting varies
slightly from range to range. Re-
adjust ZERO control each time
RANGE is changed.
3-38. USING THE CURRENT LIMIT CONTROL.
3-39. Maximum output current available at the OUT-
PUT terminals depends on both the value of the output
3-7