Specifications

4.1.4 AC Median Value Measurement (SMX2044)
To better understand the usage of this function, you should note that the DMM makes all AC voltage measurements
through an internal DC blocking capacitor. The voltage is thus “AC coupled” to the DMM. The measurement of the
Median value of the AC voltage is a DC measurement performed on the AC coupled input signal. This measurement
returns the mid-point between the positive and negative peak of the waveform. The Median value is used for setting
the comparator threshold level for best counter sensitivity and noise immunity. (It is difficult to measure the
frequency of a low duty cycle, low amplitude AC signal since there is DC shift at the comparator input due to the
internal AC coupling. The SMX2044 overcome this problem by allowing you to set the comparator threshold level).
For further information on the usage of AC Median value and Peak-to-Peak measurements, and the Threshold DAC,
see the “Frequency and Timing Measurements” section below.
This function requires a repetitive signal. The DMM must be in AC voltage measurement mode, with the
appropriate range selected.
4.2 Current Measurements
The SMX2040, 42, 44 measure from 10 ηA to 2.5 A. Use the I, 4WΩ terminals, being certain to always leave the
V,Ω + & - terminals disconnected. Use the AC/DC button to switch between AC and DC.
The Current functions are protected with a 2.5 A, 250 V fuse.
Warning! Applying voltages > 35 V to the I+, I- inputs can cause personal injury and/or damage to your
DMM and computer! Think before applying any inputs to these terminals!
When making sensitive DC current measurements, be sure to use the Relative function to zero out any residual
errors of the SMX2040. This is easily accomplished by opening all inputs to the SMX2040 and performing Relative
in the appropriate DCI range.
Figure 4-2. AC and DC Current measurement connection.
4.2.1 Improving Current Measurements
W
Signametrics 26
hen making sensitive DC current measurements, be sure to use the Relative function to zero out any residual
erro M and performing
re
mmended that whenever
rs of the SMX2040. This is easily accomplished by disconnecting all terminals to the DM
Relative in the appropriate DCI range. Using the S-Cal (DMMCalibrate()) prior to activating Relative will
improve accuracy further. Although the SMX2040 family is designed to withstand up-to 2.5A indefinitely, be awa
that excessive heat may be generated when measuring higher AC or DC currents. If allowed to rise this heat may
adversely effect subsequent measurements. In consideration with this effect, it is reco
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