Keithley 199

BASIC DMM OPERATION
2.6.6 Resistance Measurements
The Model 199 can make resistance measurements from
lmf? to 300MQ. The Model 199 provides automatic selec-
tion of Z-terminal or 4terminal resistance measurements.
Th% means that if the ohms sense leads are not connected,
the measurement is done 2-terminal. If the sense leads are
connected, the measurement is done 4terminal. For
4-terminal measurements, rated accuracy can be obtained
as long as the maximum lead resistance does not exceed
the values listed in Table 2-3. For best results on the 3WQ.
3k0 and 3OkQ ranges, it is recommended that 4terminal
measurements be made to eliminate errors caused by the
voltage drop across the test leads which will occur when
MODEL 199
----
Figure 2-5. Four-Terminal Resistance
Measurements
2-ten&al meazuements are made. The Model 5806
Kelvin Test Lead Set is ideal for low resistance 4termina.l
measurements. In the 4% digit mode, use 4terminsl or
Notes:
connect the source leads to the sense leads at the instru-
ment to avoid extra noise pickup.
1. Table 2-3 shows the current output for each resistance
range.
To ~make resistance measurements, proceed as follows:
2. It helps to shield resistance greater than 1OOkQ (or
anytime 4% digit resolution is used) to achieve a stable
1. Select the ohms function by pressing the QHMS buttqn.
2. Select a range consistent with the expected resistance
or use autoranee.
”
3. Select the front or rear panel input termirials using the
J.NruT switch.
4. For 2-terminal measurements connect the resistance to
the instrument as shown in Figure 2-4. For 4terminal
measurements connect the resistance to the instrument
as shown in Figure 2-5.
5. Take the reading from the display.
reading. Place the resistance in a shielded enclosure and
electrically connect the shield to the LO input terminal
of the instrument.
3. Diode Test-The 3kQ range can be used to test diodes
as follows:
A. Select the 3kR range.
8. Forward bias the diode by connecting the red ter-
minal of the Model 199 to the diode anode. A good
diode will typically measure between 3GGQ and IkO.
C. Reverse bias the diode by reversing the c+u-wtions
on the diode. A good diode will overrange the
display.
Shielded
Optional shield
Table 2-3. Resistance Ranges
Maximum Test Lead
S=hd Nominal Resistance (Q) for
Range Resolution I-Short ~1 Count Error (Wzd)
300 0 hnfl 1.7mA 10
3kfl lOmQ 1.7mA 30
30kR lOOmdt
le.4
100
Figure 2-4. Two-Terminal Resistance Measurements
300kR 10 5w 300
3MQ 10 n $A
Ik
30MQ 100 n O&A
3k
3ooMO 1 kO 0.5&4 30k
NOTE: Typical open circuit voltage is 5.511
2-11