Operator`s manual

47 Signametrics
measurements. The Open Terminal Calibration function must be performed with the test cable plugged
into the DMM, and open at the application side. This process characterizes the signal path including
both, DMM and cable. Set the Aperture to 160ms or to higher for better accuracy.
Particularly for low inductor values (<300uH), it is important to zero the DMM by using the ‘Relative’
function (DMMSetRelative()) while 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
and that of the application cable. The following is the general proceedure to accomplish the above:
1) Select Inductance: DMMSetFunction(nDmm, INDUCTANCE);
2) With cable open at its test end perform Open compensation: DMMOpenTerminalCal(nDmm);
3) Select a range: DMMSetRange(nDmm, _33uH); // 33uH range
4) Perform Short compensation: DMMRead(); DMMRead(); DMMSetRelative(nDmm,TRUE);
5) You are now ready to measure inductance.
Range Range symbol Range selection code Default test frequency
33µH _33uH 0 100kHz
330µH _330uH 1 50kHz
3.3mH _3300uH 2 4kHz
33mH _33mH 3 1.5kHz
330mH _330mH 4 1kHz
3.3H _3300mH 5 100Hz
Figure 4-12. Inductance measrement function default frequencies.
4.13 Characteristic Impedance Measurement (SMU2064)
To measure transmission line’s characteristic impedance, measure the cable’s capacitance C (with the end
of the cable open) and then its 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 SMU2064.
4.14 Trigger Operation
Several trigger functions are provided; some are by means of an input signal to the trigger input, and
others by means of input level.
The Trigger functions provide for a stand-alone capture of measurements. The
on-board controller supervises the operation, and when conditions are valid, it captures data into its circular buffer,
or sends it back to the PC bus. The aperture must be set to a value equal or smaller to 160ms for all trigger
operations.
4.14.1 External Hardware Trigger
The External Hardware Trigger inputs are isolated high and low input lines available at pins 7 (+) and 4 (-
) of the DIN-7 connector. The External Trigger operation may be aborted using the
DMMDisarmTrigger(). 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 35 V with respect to the PC
chassis or any other DMM terminal. Do not apply any voltages greater than 35 V to the DIN
connector pins. Violating this limit may result in personal injury and/or permanent damage to the DMM.
4.14.1.1 Edge Triggered Operation
In this mode of operation, the DMM takes between 1 and 120 (or 1 and 80 if high resolution)
measurements in response to the currently set edge. Once armed, the DMM waits for this Trigger event
until it occurs, or the process is aborted (DMMDisarmTrigr()). While waiting for the selected trigger
edge, the DMM continuously makes measurements and stored them to the internal buffer, utilizing the
whole buffer. Depending on the length of time prior to the trigger event, this circular buffer may or may
not be filled / over-written. For additional information a counter is provided to counts the number of times
the buffer fills up while waiting for the trigger event. On reception of the trigger, the DMM takes the
number of readings specified in the DMMArmTrigger() command and indicates it is ready
(DMMReady() = TRUE). These post trigger readings are stored in subsequent locations of the circular
buffer. At the end of the capture process the internal buffer pointer points to the beginning of the buffer.