Amptec Research 620A SERIES, Руководство по эксплуатации и обслуживанию

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the front panel. Replace blown fuses with the
same type and rating only!
The battery charging jack is a barrel type and is
located on the 620A rear panel. The center pin
of the connector is positive. The charging
requirements of the internal battery pack are
6VDC @300mA. The correct charging voltage
is supplied by the adapter included with the
instrument. Additional AC/DC Battery
Chargers are available as Option "DC".
The four-terminal configuration of the 620A
eliminates errors normally caused by in series
test lead resistance and contact resistances. In
many applications the contact resistance can
exceed the value of the load by several orders
of magnitude.
The 620A avoids this potential error source by
providing two terminals of constant current and
an additional two terminals for high impedance
voltage measurement. The constant current can
be thought of as a that overcomes
lead length resistance and contact resistance
encountered (all series resistance) along its loop
path. The result is a fast, accurate resistance
measurement of the load, independent of the
resistance of the current carrying leads.
Figure D-1 (above) illustrates the 4-wire
principle and how it is used to eliminate lead,
wire and contact resistances as potential error
sources. The internal current source inherently
overcomes all series resistance (within
compliance voltage limits) and delivers a
precise constant current.
The internal high-impedance DVM senses the
voltage drop across the load. There is
negligible contact and lead resistance error
created by the voltage measurement because the
high input impedance of the DVM limits
current flow in the voltage leads.
Charging Jack
D-4. 4-Wire Resistance Measurement
As a
side note, with the AMPTEC 620A-5, the
charging jack is mounted on the unit’s front
panel.
current loop
Figure D-1. Error Sources in Resistance
Measurements eliminated with Four Wire
Kelvin Connections
Connections are made to the front panel
terminals using a 4-wire configuration as
described in section 4-4. When using AMPTEC
test leads, the tabbed or
. This ensures that the
current is carried in the largest conductor and
that the voltage input is shielded. The 620A
features five way gold plated input jacks. The
gold plating on the input jacks helps minimize
thermal EMFs . Wire connections often generate
a DC offset voltage with the contact between
two dissimilar metals (also called the thermo-
couple effect).
In addition, the 620A five way input jacks allow
for clean, simple connections to bare wires,
cables terminated with spade lugs, and banana
jacks.
D-5. Connections
negative (-) side of the
banana jack is plugged into the current
terminals of the 620A
620A
CLOSEUP - INPUT JACKS (4 wire connection)
* contact resistance
4.8
VDC
BA
TTER
Y
DC CURRENT
LIMITED
CONSTANT
CURRENT
SOURCE
VOLTAGE
LIMITING
RESISTOR
IGNITER
Current
Loop
LEAD RESISTANCE
LEAD RESISTANCE
FAIL-SAFE
OHMMETER
DIGIT
AL
V
O
LTMETER
V
hi
I
hi
I
low
V
low
V high I high
V low I low
*
*