Keithley 2790 User Manual

2-10 Model 2790 SourceMeter
®
Switch System User’s Manual
High ohms calculation (SxVohms)
• SxVohms – Calculates and displays the high resistance reading for the 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 x V
SOUR
(7751)
m = -20,000 x V
SOUR
(7753)
b = 0
7751 calculation: R = m/X + b
= (-200,000 x V
SOUR
) / V
MEAS
+ 0
= -V
SOUR
/ V
MEAS
x 200,000
7753 calculation: R = m/X + b
= (-20,000 x 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
= 200kΩ).
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
= 20kΩ).
V
MEAS
is the output voltage of the V/I amplifier measured 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). This
selection also sets DMM to DCV, 10V range. 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 (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 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.

Keithley 2790 Specifications

General

Brand	Keithley
Model	2790
Category	Switch
Language	English