IET Labs HARS-LX, Руководство пользователя и обслуживания, Страница: 13 / 22

7
HARS-LX Series
7 Operation
4.4 Dial Setting
The resistance setting may be read directly from the
dial settings. For additional flexibility and range,
each decade provides a “10” position setting. This
“10” position on any one decade equals the “1” posi-
tion on the next higher decade if any. It adds about
11% to the nominal total decade resistance. The
most significant decade also has an “11” position
to extend the resistance range to over 1.2 M Ω . The
l0 m Ω decade, however, does not go below the
“1“ position in order to maintain a precise and
constant minimum resistance of 10 m Ω , so that no
subtraction of zero resistance is required.
To determine the resistance obtained when any one
or more “10” or “11” settings are used, simply add 1
to the next higher decade. For example, a setting of
“10-11-10-10-10-10” becomes:
11 1 1 0 0 0 0
10 1 0 0 0 0
10 1 0 0 0
10 1 0 0
10 1 0
10 1
1
10
Total 1 2 1 1 1 1
In order to obtain a zero in the l Ω position, set the
l Ω decade to the “10” position, i.e. l0 Ω , and take the
l0 Ω setting, in the next decade, into consideration.
To get 2 Ω , for example, the switches should be set
to show “1-10”.
Since the highest decade has an additional “11” po-
sition, resistance values of over 1.2 times nominal
maximum value can be obtained.
4.5 Power Considerations
To maintain the maximum possible accuracy and pre-
cision, power applied to the HARS-LX should be kept
as low as possible, preferably below 0.1 W. For best
protection of the instrument, it is advisable to limit
the input power to 1 W. This may be implemented
with a series resistor or fuse.
4.6 Environmental Conditions
For optimal accuracy, the decade box should be used
in an environment of 23ºC. It should be allowed to
stabilize at that temperature for at least four hours
after any significant temperature variation.
Humidity should be maintained at laboratory condi-
tions of 30% to 70% RH.
4.7 Switch Conditioning
The switch wipers employed in this unit are self
cleaning. They have solid silver alloy contacts.
After being left idle, the wipers and contacts must
be conditioned or “broken in” again to remove the
film of silver oxide that develops over time. This is
standard metrology practice when high accuracy is
required. This effect is of the order of less than 1 m Ω ,
So it may be ignored whenever measurements of that
magnitude are not important.
To perform this “breaking in,” simply rotate each
switch seven to ten times in each direction.