Keithley 2790 User Manual page 31

2-10
High ohms calculation (SxVohms)
•
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 x V
m = -20,000 x V
b = 0
7751 calculation: R = m/X + b
7753 calculation: R = m/X + b
where:
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). This
selection also sets DMM to DCV, 10V range. Note that the V
(-). 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 (SxVohms), 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).
If V> - 10mV, an overflow will occur. If V< -12V, an underflow will occur.
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.
NOTE
SxVohms – Calculates and displays the high resistance reading for the 7751/7753
module in slot x (where x =1 or 2).
(7751)
SOUR
(7753)
SOUR
= (-200,000 x V
= -V
SOUR
= (-20,000 x V
= -V
SOUR
V is the programmed voltage level of the V-source of the 7751/7753.
SOUR
For the 7751, (-200,000 x V
200,000 is the value of the feedback resistor (R
(R = 200kΩ).
F
For the 7753, (-20,000 x V
20,000 is the value of the feedback resistor (R
V is the output voltage of the V/I amplifier measured by the DMM of the
MEAS
Model 2790. It is the "X" variable for the calculation (m/X+b).
Readings for both the 7751 and 7753 modules will overflow when the I/V output
is greater than -9mV and underflow when the I/V output is less than -12V.
Model 2790 SourceMeter
) / V + 0
SOUR MEAS
/ V x 200,000
MEAS
) / V + 0
SOUR MEAS
/ V x 20,000
MEAS
) is the "m" factor for the calculation (m/X+b).
SOUR
) is the "m" factor for the calculation (m/X+b).
SOUR
) for the I/V amplifier (R
F
®
Switch System User's Manual
) for the I/V amplifier
F
F
reading will be negative
MEAS
= 20kΩ).