Figure 2-11 Coulombs Connections - Keithley 6512 Instruction Manual

Normal charge measurements
Use the following procedure to measure charge with the
Model 6512:
1. Turn on the power, and allow a two-hour warm up peri-
od for rated accuracy.
2. Place the instrument in the coulombs mode by pressing
the COUL button. Set V, Ω/ GUARD to OFF.
3. To achieve rated accuracy, place the instrument on the
200pC range, and zero the instrument by enabling zero
check and then pressing the ZERO CORRECT button.
4. Select the desired range, or use auto-ranging, if desired.
5. Disable zero check. A small amount of zero check hop
(sudden change in the reading) may be observed when
OFF
V, Ω GUARD
Q S
Figure 2-11
Coulombs connections
TRIAX CABLE
INPUT
ON
MODEL 6512
INPUT AMPLIFIER
C F
1000pF
HI
LO
S
GND
PREAMP
OUT
COM
zero check is disabled. If desired, enable suppress to null
out any zero check hop, which typically will be in the
10-25 count range.
6. Connect the triax cable to the INPUT jack. Connect the
other end of the cable to the circuit being measured, as
shown in Figure 2-11. For low-level measurements,
shielding may be required.
Do not connect the circuit to the instru-
ment with zero check enabled.
7. Read the charge value from the display. The exponent
may be placed either in the alpha or numeric modes as
described in paragraph 2.5.
NOTE: LEAVE Q S DISCONNECTED
HI
LO
A. CONNECTIONS
S
100Ω
B. EQUIVALENT CIRCUIT
NOTE
UNTIL ZERO CHECK DISABLED
Q S
MEASURED
CHARGE
SHIELD (OPTIONAL)
TO A/D
CONVERTER
2V ANALOG
OUTPUT
S
Operation
2-15