1Ona And 1Na Range Verification - Keithley 220 Instruction Manual

7. Using the measured value of the 1OMR resistor, calculate
the voltage drop ecross that resistor.
Example: f + 1 .OOOO-6A) x llO.OOlMQ) = lO.OOlOV.
IModel 220 Programmed Output1 x (Measured
Resistance) = (Expected Voltage Drop Across RI.
8. Verii that the reading on the Model 192 is the calculated
voltage drop f0.0165V.
9. Place the Model 220 in the standby mode and take the
Model 192 out of the zero mode (ZERO annunciator off).
10. Set the Model 192 to the 2VDC range.
11. Cancel the effects of guard offset from the Model 220 as
follows:
A. Program the Model 220 to output +OOO.O-9A.
B. Short the 10MQ resistor.
C. Zero the display of the Model 192 by pressing the
ZERO button.
D. Remove the short from the 1OMD rasistor.
12. Program the Model 220 to output + lOO.O&9A with a
20V compliance.
13. Using the measured value of the 1OMB resistor, calculate
the voltage drop across that resistor.
Example: f+ lOO.OO-9A) x (lO.OOlMD) = l.OOOlOV.
(Model 220 Programmed Output) x (Measured
Resistance) = (Expected Voltage Drop Across RI.
14. Verify that the reading on the Model 192 is the calculated
voltage drop *O.O0367V.
15. Repeat steps 4 through 14 with negative current output
16. Place the Model 220 in the standby mode and take the
Model 192 out of the zero mode
r--------i
1. To decrease settling times and to assure accurate calibrations. it is
recommended to use an internal guard Ias shown in the drawing
aboveI. The guard mwf be insulated from the surrounding case.
2. To further minimize inaccuracies. current leakage paths to ground for
guardl mwst be minimized. This requires the use of low leakage insu-
Ming materials for conStruction and the use of special cleansing agents
such as freona
to clean the components and insulators after construe-
don.
Figure 3-2. Test Fixture
3.6.4 1OnA and 1nA Range Verification
1. Construct the test fixture shown in Figure 3-2 using the
1GD resistor specified in Table 3-l.
2. Measure the 1GR resistor with the Guildline 9520 and
note the value.
3. Set up the circuit shown in Figure 3-3.
4. Set the Model 192 to the 20VDC range.
5. Cancel the effects of guard offset from the Model 220 as
follows:
A. Program the Model 220 to output O.OOO-9A.
B. Short the 1Gfl resistor.
C. Zero the display of the Model 192 by pressing the
ZERO button.
D. Remove the short from the IGQ resistor.
6. Program the Model 220 to output C lO.OOO-9A with a
20V compliance.
7. Using the measured value of the 1GD rssistor, calculate
the voltage drop across that resistor.
Example: f + 10.0009A) x fl.OOlGfB = lO.OlOOV.
(Model 220 Programmed Output) x (Measured
Resistance) = (Expected Voltage Drop Across R).
8. Verii that the reading on the Model 192 is the calculated
voltage drop *O.O34OV.
9. Place the Model 220 in the standby mode end take the
Model 192 out of the zero mode.
10. Set the Model 192 to the 2VDC range.
11. Cancel the effects of guard offset from the Model 220 as
follows:
A. Program the Model 220 to output + .OOOO-9A.
B. Short the 1GQ resistor.
C. Zero the display of the Model 192 by pressing the
ZERO button.
D. Remove the short from the 1GR resistor.
12. Program the Model 220 to output + 1 .OOOO-9A with a
20V compliance.
13. Using the Measured value of the 1GD resistor, calculate
the voltage drop across that resistor.
Example: f + 1.00069A) x fl.OOlGD) = .OOlOOV.
(Model 220 Programmed Output) x (Measured
Resistance) = fExpsctad Voltage Drop Across RI.
14. Verify that the reading on the Model 192 is the calculated
voltage drop *0.00542\1.
15. Repeat steps 4 through 14 with negative current output.
Figure 3-3. lpA-1nA Range Verification
3-313-4