6
PRS-200 Series
OPERATION
Chapter 3
OPERATION
The
GND
terminal on all models is connected to the
case and to earth and chassis grounds. This may be
used as a shield terminal.
3.2.2 Electrical Considerations
The performance of the PRS-202 is directly affected
by the quality of the connection to the system under
test. This is particularly true with the precision series
models equipped with higher accuracy, lower imped-
ance decade values.
For optimum performance, contact resistance should
be kept to a minimum using the most substantial mat-
ing connection practically possible, and assuring the
connection is well secured to the binding posts.
3.2.3 Four-Wire Kelvin Lead Connections
4-wire Kelvin leads minimize the effects of contact
resistance and approach ideal performance. The
CURRENT
and
SENSE HI
/
LO
terminal pairs may
be shorted together to provide a 2-terminal load in
instances where high accuracy is not a concern.
3.2.4 Thermal emf Considerations
The PRS-202 Series uses high quality, low emf com-
ponents. Thermal emf is primarily attributable to the
temperature difference between the leads of the re-
lay and the contacts when temperature is applied to
the coil. This emf is of the order of 5 V per relay,
but is not usually additive. The typical worst case is
<15
µ
V.
3.1 Initial inspection and setup
This instrument was tested and carefully inspected
before shipment. It should be in proper electrical and
mechanical order upon receipt.
An
OPERATING GUIDE
is attached to the case
of the instrument to provide ready reference to speci-
fications.
Mount the unit in a standard 19" rack if the rack mount
option is specified.
3.2 Connection
3.2.1 General Considerations
The PRS-202 Series Decade unit is available in three
or five terminal versions. The binding posts are stan-
dard laboratory type and readily accept banana plugs,
telephone tips, spade lugs, alligator clips, and bare wire.
Binding posts are located on the front panel of the
instrument unless specifically ordered with a Rear
Output option.
The three terminal version posts are labeled
HI
,
LO
,
and
GND
. The
HI
and
LO
terminals are connected
to the ends of the internal impedance being set.
5 terminal models provide four Kelvin terminals con-
sisting of a
CURRENT
and a
SENSE
pair, each
labeled
HI
and
LO
. These minimize contact resis-
tance.
