Keithley 263 Instruction Manual page 33

OPERATION
MODEL 263
I-_-_--_____-__----_-------~
/ I
Figure 3-2. Voltage Source
approximately 99.99% of Vs will be delivered to the load.
This 0.01% additional error will degrade basic volts ac-
curacy from 0.0175% to 0.0275%. The actual voltage
delivered to the load can be calculated as follows:
V, x Ri
vowr =
(R, + R,)
where
V OuT = Voltage delivered to the load
V, = Voltage setting of the 263
R, = Resistance of the load
Rs = Output resistance of the source (10)
If the load is <lOOkO, additional error is calculated as
follows:
10
Additional Error (%) =
x 100
Load Resistor + la
External Source (EXT INPUT)
EXT INPUT is provided so that the Model 263 can switch
select an external source of up to 2OOV and lOOmA. This
feature eliminates the need to physically disconnect the
Model 263 from the device under test (DUT) in order to
connect an external source to the DUT. This is particular-
ly handy when running automated test programs over the
IEEE-488 bus.
Since internal VOLTS only outputs up to k19.9995 and
+ 19.9995mA, an external source can be used to calibrate
instruments that have higher voltage and current require-
ments. A simplified circuit showing an external source
connected to EXT INPUT is shown in Figure 3-3. Maxi-
mum inputs for EXT INPUT are 200V peak and lOOmA
peak. Staying within these limits will protect the Model
263 from damage.
As with the internal voltage supply, connecting a high im-
pedance device (such as an electrometer) to the output will
not result in any loading problems. For low resistance
loads and high currents, EXT INPUT circuit resistance (In)
should be taken into account. When sourcing voltage
through the Model 263, use the following equation to
calculate voltage drop through the Model 263:
where
V = Voltage drop through the 263.
R LXT = Output resistance of the external voltage source.
R LoAD = Load resistance.
V E.77 = Voltage setting of the external source.
3-3