13
OPERATION
HPRS Series
Chapter 4
OPERATION
4.1 General Considerations
The
HPRS
Series Decade unit provides three termi-
nals labeled
H
(high),
L
(low), and
G
(ground.) The
H
and
L
terminals are connected to the ends of the
resistor being set. the
G
terminal is connected to the
case. The
G
terminal may be used as a guard or shield
terminal. It may also be connected using a shorting
link to either terminal to allow two-terminal as op-
posed to three-terminal measurement. See Figure 5.1.
In order to make proper use of the full performance
capabilities of the HPRS unit, especially if low re-
sistance or high power are important, take care in
connecting to the terminals of the decade box.
In order to keep contact resistance to a minimum,
make the most substantial and secure connection to
the binding posts. They accept banana plugs, tele-
phone tips, spade lugs, alligator clips, and bare wire.
The largest or heaviest mating connection should be
made, and, where applicable, the binding post should
be securely tightened.
4.2 Duty Cycle
It is important to keep the amount of time power is
applied the the HPRS within the duty cycles below.
The duty cycles assume an ambient temperature of
around 23
0
C.
Power
Time on
Time off
<101 W
continuous
none
>101 W
5 minutes
10 minutes
Exceeding the time on can cause damage to the resis-
tors. If continuous use is required to full rated power
see DRS-900 High Power Resistance Substituter.
4.3
Electrical Considerations
As a good safety practice, the case should be grounded
using the
G
terminal.
Since high voltages may be present, it is important to
observe all precautions and safety rules.
•
CONNECT THE G (GND) TERMINAL TO
EARTH OR OTHER SUITABLE
GROUND IN
ORDER TO MAINTAIN THE CASE AT A SAFE
VOLTAGE.
•
WHENEVER HAZARDOUS VOLTAGES (>45 V)
ARE USED, TAKE ALL MEASURES TO AVOID
ACCIDENTAL CONTACT WITH ANY LIVE
COMPONENTS:
•
-USE MAXIMUM INSULATION AND MINIMIZE
THE USE OF BARE CONDUCTORS.
•
- REMOVE POWER WHEN SETTING
SWITCHES.
•
EXERCISE CARE WHEN HANDLING UNIT.
CASE - ESPECIALLY REAR AND BOTTOM
MAY BECOME HOT IF HIGH POWER IS AP-
PLIED FOR AN EXTENDED PERIOD.
•
POST WARNING SIGNS AND KEEP
PERSONNEL SAFELY AWAY
.
4.4 Dial Setting
Whenever the dials are used for positions 0-9, the
resulting resistance is simply read from the panel dial
setting directly. Both the decimal point and the steps
are clearly marked on the panel.
4.5 Environmental Conditions
For optimal accuracy, the decade box should be used
in an environment near 23
0
C and <50% RH. It should
be allowed to stabilize at those conditions for at least
two hours after any signifi cant temperature variation.
