Operator`s manual

Figure 4-11. Measuring capacitors or inductors is best handled with low capacitance shielded probes.
4.10 In-Circuit Capacitance Measurement (SMU2064)
A second method for measuring capacitance is the AC based method. This function consists of six ranges,
24nF to 24mF. Though not as accurate or fast as the above function, it is able to measure capacitance
which is burdened with low parallel impedance. This function is more comlex for use, and should only be
used if the Charge Balance method does not work. The default stimulus is set at 0.45V peak, preventing
semiconductor junctions to conduct. It is also possible to control the stimulus voltage. This test function
operates by measuring the complex impedance and extracting from it both, the capacitance and resistance.
The measurement is practical down to a few hundred Pico Farads, and up to several thousands micro
Farads, with parallel resistances as low as 20 depending on range. Following the selection of this
function (DMMSetFunction(0, 82)), use DMMRead(), DMMReadStr() and DMMReadNorm() to
measure the capacitance value. The resistive component can be read using DMMGetACCapsR()
following a reading. It is necessary to calibrate each range prior to making measurements. This is done by
selecting the desiered range (DMMSetRange()) and performing open terminal calibration using
DMMOpenCalACCaps() function. Make sure nothing is connected to the test leads while doing this.
This process will calibrate only the selected range. It is best to use the default stimulus level. However, if
this level is changed (DMMSetACCapsLevel()), repeate the open terminal calibration. The calibration
factors are preserved, for each range as long as the driver (DLL) remains loaded. The
DMMSetACCapsDelay() is provided to allow control over the internal measurement delay, as well as
range limits. A delay value of 0 to 10s can be set (it has little effect on the three upper ranges). To remove
range limits (i.e. measure 5uF while in the 2.4uF range), the delay is set to a negative value. For instance
setting it to -0.1 will result in 100ms delay and no range limits. With the test leads connected to the DMM
terminals, use the Relative function (DMMSetRelative()) to take out any offset due to cables. The
stimulus frequency may be read using the DMMGetSourceFreq() function. The default frequencies,
starting at the lowest range are: 100kHz, 10KHz, 1kHz, 100Hz, 20Hz and 4Hz. For best results Set the
DMM Aperture for 33ms or higher. Or use the delay in conjuncton with a smaller aperture. An additional
modifier to this function is the DMMSetSourceRes() function.
Additional considerations
Lead resistance (overall path resistance, including swithing and interconnects) should be kept below 1
Ohm. The selected aperture must be an integer value multiple of 1/test frequency. When testing polarized
capacitors the DMM’s positive terminal must be connected to the corresponding terminal of the capacitor.
Capacitors with high ESR will read lower than their nominal value.
4.11 Measuring the resistance in a series RC network (2064)
A method for measuring the resistance of a series RC network is provided, which comlements the two
Capacitance measurement methods. The value of the resistor (ESR) is measured using an AC source in a
ratiometric method, which relies on a calibrated and characterized internal source resistance. To perform
this measurement use the following sequence of commands:
45 Signametrics