Operator`s manual

Signametrics 34
4.0 DMM Operation and Measurements Tutorial
Most of the DMM’s measurement functions are accessible from the Windows Control Panel (Figure
above). All of the functions are included in the Windows DLL driver library. To gain familiarity with the
SMU2060 series DMM’s, run the Windows ‘SETUP.EXE’ to install the software, then run the DMM, as
described in the previous section. This section describes in detail the DMM’s operation and measurement
practices for best performance.
4.1 Voltage Measurement
Measures from 0.1 V to 330 VDC or 250 VAC. Use the V,2 + and V, 2 - terminals, being certain to
always leave the I,4+ and I,4- and DIN-7 terminals disconnected. Use the AC/DC button on the
Control Panel to switch between AC and DC.
Making Voltage Measurements is straightforward. The following tips will allow you to make the most
accurate voltage measurements.
4.1.1 DC Voltage Measurements
When making very low-level DCV measurements (<1 mV), you should first place a copper wire shorting
plug across the V, 2 + and V, 2 - terminals and perform Relative function to eliminate zero errors
before making your measurements. A common source of error can come from your test leads, which can
introduce several Volts of error due to thermal voltages. To minimize thermal voltaic effects, after
handling the test leads; you should wait a few seconds before making measurements. Signametrics offers
several high quality probes that are optimal for low-level measurements.
Note: The front panel powers up in DCV, 0.5s aperture, 240 V range. If the DMM is operated in
Autorange, with an open input, The DMM will keep changing ranges. This is perfectly normal with ultra
high impedance DMM’s such as the SMU2060. The virtually infinite input impedance of the 240 mV and
2.4 V DCV ranges causes this phenomenon. On these ranges, an open input will read whatever charge is
associated with the signal conditioning of the DMM. As this electrical charge accumulates, the
SMU2060 will change ranges.
4.1.2 True RMS AC Voltage Measurements
ACV is specified for signals greater than 1mV, from 10 Hz to 100 kHz. The ACV function is AC
coupled, and measures the true RMS value of the waveform. As with virtually all true-RMS measuring
meters, the DMM may not read a perfect zero with a shorted input. This is normal.
In ACV measurements it is important to conenct NEUTRAL or GROUND signal being measured to the
DMM’s V,2 - terminal. This prevents any “Common Mode” problems from occurring (Common Mode
refers to floating the DMM V,2- voltage referenced to Earth Ground.) Common Mode problems can
result in noisy readings, or even cause the PC to hang-up under high V X Hz input conditions. In many
systems, grounding the source to be measured at Earth Ground (being certain to avoid any ground loops)
can give better results.
The settling time and low frequency limits of the RMS functions (AC Voltage and current) are effected
by the state of the Fast RMS control circuit. This function is off as a default. When Fast RMS is selected
(see
DMMSetFastRMS), the RMS settling time is about 10 times faster, but the low frequency cutoff point
is increased significantly. For minimum error engage the Fast RMS at signals frequencies higher than
400Hz. Using the Read Interval (DMMSetReadInterval) in conjunction with aperture
(DMMSetAperture) will facilitate accurate control over the settling and measuring times. For instance,
when measuring 1.5V 1kHz signal using the 2.4V ACV range, optimize speed by setting the DMM for
Fast RMS, set Aperture to 66.6ms and the Read Interval to 116.6ms. This will provide the required RMS
processing time of 50ms.