Signametrics
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4.0 DMM Operations and Measurements
Most of the SMX2040 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 SMX2040 series
DMMs, 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
µ
V to 300 VDC or 250 VAC. Use the
V,
Ω
+
and
V,
Ω
-
terminals, being certain to always leave
the
I+, I-
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 (<100
µ
V), you should first short the DMM with a copper wire
shorting plug across the
V,
Ω
+
and
V,
Ω
-
terminals and perform the
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
µ
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 SMX2040 front panel powers up in DCV, 2 readings per second,
330
V range. If the DMM is operated in
Autorange, with an open input, you may hear the SMX2040 relays clicking every few seconds, as a range change
occurs. This is perfectly normal with ultra high impedance DMMs such as the SMX2040. This phenomenon is
caused by the virtually infinite input impedance of the 330 mV and 3.3 V DCV ranges. On these ranges, an open
input will read whatever charge is associated with the signal conditioning of the DMM. As this electrical charge
changes, the SMX2040 will change ranges, causing the relays to click. This is normal.
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