Keithley 2790, Справочное руководство

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Model 2790 SourceMeter
®
Switch System Reference Manual 5-13
SxVohms
Calculates and displays the high resistance reading for 7751/7753 module in slot x (where
x =1 or 2). This ohms function is a shortcut for the m/X+b calculation. When selected, the
following “m” and “b” factors are used:
m = -200,000
×
V
SOUR
(7751)
m = -20,000
×
V
SOUR
(7753)
b = 0
7751 calculation:
R = m/X + b
= (-200,000
×
V
SOUR
) / V
MEAS
+ 0
= - V
SOUR
/ V
MEAS
x 200,000
7753 calculation:
R = m/X + b
= (-20,000
×
V
SOUR
) / V
MEAS
+ 0
= - V
SOUR
/ V
MEAS
x 20,000
where: V
SOUR
is the programmed voltage level of the V-source of the 7751/7753.
For the 7751, (-200,000 x V
SOUR
) is the “m” factor for the calculation (m/X+b).
200,000 is the value of the feedback resistor (R
F
) for the I/V amplifier (R
F
=
200k
Ω
).
For the 7753, (-20,000 x V
SOUR
) is the “m” factor for the calculation (m/X+b).
20,000 is the value of the feedback resistor (R
F
) for the I/V amplifier (R
F
=
20k
Ω
).
V
MEAS
is the measured voltage by the DMM of the Model 2790. It is the “X” variable for
the calculation (m/X+b).
When the SxVohms calculation is selected, the Model 2790 measures voltage (X) and
calculates m/X+b using the above factors. The displayed reading will be in ohms (
Ω
).
Note that the V
MEAS
reading will be negative (-). Because the output of the V/I amplifier
is inverted, the negative value of “m” will cause the ohms reading to be displayed as a
positive value.
When using the high ohms calculation, the highest DCV measurement range that can be
selected is 10V. Attempting to select a higher range will cause error -222 (Parameter out of
range). Attempting to turn autoranging on generates error -221 “Settings conflict” over the
GPIB or a “NO AUTORANGE” message on the display if done from the front panel
AUTO key.
SxVohms overflow rules: If V> - 10mV, overflow occurs. If V< -12V, underflow occurs.