Dc Voltage Measurement - Datron 1061A User Handbook Manual

DC
voltage
measurement procedure
4
Connect
guard.
if
remote guard
_ 2
Select
range
selected
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5
Apply
signal to
'Hi'
and
'Lo'
terminals
3
Select
filter
if
required
(1061 A: 6V2 digits)
(1071 :7'/2 digits)
Simple lead connection
For
the
majority of applications the
simple lead
connection
shown
below with
'Local
Guard'
selected will
be
adequate.
The disadvantage of
this
simple
arrangement
is
that the
connecting
leads
form
a loop. If
a
stray alternating
magnetic
field,
e.g.
from
the
line
transformer of a
neighbouring
instrument, passes
through
the
loop
it
will
behave
as
a single
turn
secondary winding inducing
unwanted
AC
voltages into
the
measuring
circuit.
Use of a
twisted pair
will
reduce the
loop area
as
adjacent
twists will
automatically
cancel
any
induced
voltages. If
problems
with
stray
pick-up are
encountered,
it
is
recommended
that
a
screened
twisted pair
cable
be used with
the
screen
connected
to the 'Lo'
or 'Guard' terminal.
ran
Hold Ratio
Test Spec
Av
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MODE.
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C
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fA~B)
+C
Max Min
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COMPUTE.
'
1 Select
DC
flowing
in
the
measuring
circuits,
are
minimised
by
providing a separate
common
mode
current path
as
shown
in
the
examples
below.
Use
of
remote guard connection
The 'Guard' terminal should be used with
'Remote
Guard'
selected
when
the
source
to
be
measured
presents
an unbalanced impedance
to the
measuring
terminals
and
common mode
voltages are present.
Regardless of
how
the 'Hi'
and
'Lo'
terminals are
connected, the 'Guard' terminal should refer to
the
source of
common
mode
voltage. This will
ensure
that errors,
caused by
common mode
currents
'GUARD"
—
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ill
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2
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r
-4
Cil_R
3
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eL
RL
Cl
=
Input
impedance
R2,
C2
=
Input to guard
leakage
impedance
R3,
C3
=
Guard
to case
leakage
impedance
Vcml,
Vcm2
= Common
mode
voltages
2-4