Signametrics
34
s the AC based method. Though not as accurate as the above
nction, the advantage of this method is that the default stimulus is set at 0.45V peak, which is lower than a
nge of voltages. A further advantage is the
t
ge to be calibrated and issuing
DMMOpenCalACCaps()
.
The last function normalizes
open
alibration and measurements. Since the DMM is optimized for this value, and it is well below most semiconductors
ltage can be set from
q()
.
ment (SMX2044)
he
urce with a frequency range of 20 Hz to 75 kHz. Since
indu
e the appropriate generator frequency. In addition to
or
,
.10 Characteristic Impedance Measurement (SMX2044)
uctance are within the
ecified measurement range of the SMX2044.
he Trigger functions provide for a stand-alone capture of measurements. The local controller supervises the
oper
s it back to the PXI bus. The reading
r
be at a low logic level (inactive). While using the PXI trigger inputs as the trigger source,
e External Hardware trigger must at a low logic level, or disconnected. Failing to do this will result in a disabeled
trigger. The PXI and External Hardware trigger software functions includes:
DMMArmTrigger
, which responds to
4.8 In-Circuit Capacitance Measurement (SMX2044)
A second method provided for measuring capacitors i
fu
semiconductor junction on voltage. It may also be set over a wide ra
ability of this function to measure capacitors that have a very low value parallel resistance, which is impossible to
do using conventional methods. This test function operates by figuring 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
Ω
to 300
Ω
depending on range. Once set to
this function, use
DMMRead()
,
DMMReadStr()
and
DMMReadNorm()
to measure the capacitance value. To ge
the resistance value use
DMMGetACCapsResist()
following a read. Each of the ranges must be calibrated with
open terminals prior to making measurements. Each range must be calibrated. Do this by activating the AC-Caps
unction, selecting the ran
f
the AC source signal. This open Calibration operation must be performed with the measurement cable or probes
plugged into the DMM, with the other end open. See figure 4-9 above for connection. If not modified by the
DMMSetACCapsLevel()
function, when making a measurement the DMM uses a default voltage of 0.45Vpk,
hich means that a sine wave that has a peak-to-peak amplitude of 0.9V. This level is used during both,
w
c
On voltage, it is recommended not to change the level from this default value. The stimulus vo
0.1V peak to 5V peak using the
DMMSetACCapsLevel()
function. Any time the stimulus level is adjusted; open
calibration must be carried out. The results of
DMMOpenCalACCaps()
are kept in memory until the DLL is
unloaded. Repeating Open calibration periodically will result in improved accuracy. AC Capacitance measurement
function must be used with a DMM reading rate of 10rps. Other functions of interest for this operations are
MMSetACCapsDelay()
and
SetACCapsFre
D
4.9 Inductance Measure
T
SMX2044 measures inductance using a precision AC so
ctors can vary greatly with frequency, you should choos
inductance, the inductor’s Q factor can be measured. A shielded, high quality cable is highly recommended. F
best accuracy, perform the Open Terminal Calibration function within an hour of inductance measurements. The
Open Terminal Calibration function must be performed with the cables plugged into the DMM, but with the other
end open circuited. This process characterizes the internal signal path inside the DMM, the open application cable
and the DMM circuitry.
For best measurement accuracy at low inductance values, zero the DMM often by using the ‘
Relative
’ function with
the leads shorted. This must be done following Open Terminal Calibration operation. This Relative action measures
and removes the inductance of the DMM signal path including that of the application cable being used.
4
To measure a transmission line’s characteristic impedance, measure the cable’s capacitance C (with the end of the
cable open) and then it’s inductance L (with the end of the cable shorted). The cable’s impedance equals the square
root of L/C. Be certain the cable is long enough such that both the capacitance and ind
sp
4.11 Trigger Operation
4.11.1 External Hardware Trigger
T
ation, and when conditions are valid, it captures data into its buffer, or send
rate must be set to 10 rps or higher. The External Trigger’s isolated high and low input lines are provided at pins 7
(+) and 4 (-), respectively, on the DIN connector located on the front panel of the instrument. You may abort the
External Trigger’s wait state using the Disarm command. It is important to note that the External Hardware Trigge
is
Wire-Ored
with the PXI triggers. Therefore, while using the External Trigger, the PXI trigger input line selected
see section 4.11.4) must
(
th
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