Table of Contents
Advertisement
=
g-EMENTS
(Cont'd)
ESISTANCE
ME,
MELO
P-L
.
iL
| Command
Other Considerations
1. There
are
two
situations
in which
the
3468A
may
indicate
a negative
(minus) resistance. One is when small negative voltages exist on the circuit under
test. The second is where the inputs to the 4-WIRE SENSE and the input leads are
inverted from each other in the 4-wire ohms function.
2. Always use the shortest possible test leads. This is important on the lower
ranges to minimize errors due to lead resistance (2-wire ohms mode), and on the
higher ranges to minimize noise pick up.
3. Additional settling time may be required when using the higher ohms ranges
under
program
control.
This
is important
if there
is more
than
F shunt
capacitance
connected
externally
as might be the case
if you
were
using the
3468A with a scanner. Theoretically, the settling time necessary is:
—RC*In(P/100)
Where R is the resistance being measured, C is equal to $56pr plus any external
Capacitance, and P is the desired percentage of step accuracy. For example, lets
say we want to measure
a 3.0 Mohm
resistor through a scanner
with
1200pF
capacitance (High-to-Lo terminals). If a short was previously applied (short to 3.0
Mohms
= step) and a .001%
reading is desired, the settling time necessary
is:
o
~ (3108) +(1 200 + $88} «(10-12)«{In(.001/100)) = £3mns
Singe on the 3 Mohm range there is an internal delay of 20mS, an additional delay
of
to a8 mS should be allowed. The 30 Mohm range has an internal delay of
200
mS.
24
.
Advertisement
Table of Contents
