6
PRS 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 is directly affected by
the quality of the connection to the system under test.
This is particularly true with the precision series mod-
els having higher-accuracy and/or lower-impedance
decades.
For optimum performance, contact resistance should
be kept to a minimum by using the most substantial
mating connection possible, and by assuring that 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 connec-
tion in instances where high accuracy is not a con-
cern.
3.2.4 Thermal emf Considerations
The PRS Series uses high-quality, low-emf compo-
nents. Thermal emf is primarily attributable to the tem-
perature difference between the leads of the relay
and the contacts when temperature is applied to the
coil. This emf is of the order of 5 µV 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 Series Decade unit is built in 3-terminal or
5-terminal versions. The binding posts are standard
laboratory type and readily accept banana plugs, tele-
phone 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 3-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.
PRS-202 IEEE.2/05-12-05
