Operator`s manual

Signametrics 34
bility of this function to measure capacitors that have a very low value parallel resistance, which is impossible to
do u unction operates by figuring the complex impedance and extracting from
to
es
nction. Any time the stimulus level is adjusted; open
4.9 Inductance Measurement (SM2044)
The SM2044 measures inductance using a precision AC source with a frequency range of 20 Hz to 75 kHz. Since
inductors can vary greatly with frequency, you should choose the appropriate generator frequency. In addition to
inductance, the inductor’s Q factor can be measured. A high quality coaxial or at least a shielded cable is highly
recommended. For best accuracy, perform the Open Terminal Calibration function within an hour of inductance
measurements. The Open Terminal Calibration function must be performed with the cable or probes 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. Set the measurement rate to 10 rps or lower for best
accuracy.
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 after Open Terminal Calibration operation. This Relative action measures and
removes the inductance of the DMM signal path and that of the application cable.
4.10 Characteristic Impedance Measurement (SM2044)
To measure 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 inductance are within the
specified measurement range of the SM2044.
4.11 Trigger Operation
Several trigger functions are available; some are by means of an input signal to the trigger input, and
others by means of measured level.
4.11.1 External Hardware Trigger
The Trigger functions provide for a stand-alone capture of measurements. The local controller supervises the
operation, and when conditions are valid, it captures data into its buffer, or sends it back to the PC bus. The reading
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. You can abort the External Trigger modes by sending the DMM
the Disarm command. The hardware trigger functions include: . Read about these functions in the Windows
Command Language section (5.6) for details.
Warning! The DIN connector pins are only protected to a maximum of 30 V with respect to the PC chassis
or any other DMM terminal. Do not apply any voltages greater than 30 V to the DIN connector pins.
Violating this limit may result in personal injury and/or permanent damage to the DMM.
a
sing conventional methods. This test f
it both, the capacitance and resistance. The measurement is practical down to a few hundred Pico Farads, and up
several thousands micro Farads, with parallel resistances as low as 20Ω to 300Ω depending on range. Once set to
this function, use DMMRead(), DMMReadStr() and DMMReadNorm() to measure the capacitance value. To get
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
function, selecting the range to be calibrated and issuing DMMOpenCalACCaps(). The last function normalizes
the AC source signal. This open Calibration operation must be performed with the measurement cable or prob
plugged into the DMM, with the other end open. See figure 4-9 above for connection. If not modified by the
MMSetACCapsLevel() function, when making a measurement the DMM uses a default voltage of 0.45Vpk,
D
which means that a sine wave that has a peak-to-peak amplitude of 0.9V. This level is used during both, open
calibration and measurements. Since the DMM is optimized for this value, and it is well below most semiconductors
On voltage, it is recommended not to change the level from this default value. The stimulus voltage can be set from
.1V peak to 5V peak using the DMMSetACCapsLevel() fu
0
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.