4.13.2 AC Voltage Source
The AC voltage source is fully isolated. It has two modes of operation: fast settling or closed loop. In the
Closedloop mode, the source voltage is monitored, and corrections are made to the composite 16 bit DAC at a rate
proportional to the set measurement rate. A 10 rps or lower reading rate is recommended for the Closedloop mode.
The Closedloop mode offers the best accuracy. In the fast settling mode, the source voltage is monitored and can be
displayed, but no DAC adjustments are made. Both amplitude and frequency can be set. The frequency range is
2 Hz to 75 kHz, and the amplitude is up to 20 V peak-to-peak with 10 mA maximum peak current drive. The output
impedance is approximately 250
Ω
.
Figure 4-15. Generating AC voltage. The figure indicates the internal monitoring of the output in closed
loop operation.
4.13.3 DC Current Source
The SMX2044 has a fully isolated unipolar DC current source with five ranges. It uses the 12 bit DAC to control
current level. This source function is useful for parametric component measurements as well as for system
verification and calibration, where a precise DC current is necessary to calibrate current sensing components.
For improved resolution of the current source, use the Trim DAC. It has to be set separately, since it is not included
in the calibration record, or the control software. Use DMMSetTrimDAC() command with a parameter of 0 to 100.
Further details are in Chapter 6.
4.13.4 Source Current - Measure Voltage
When sourcing current and measuring voltage, there are two connection configurations: 1) Four wire connection,
where the current sourcing terminals and the voltage sense terminals are connected to the load, as in 4-wire Ohms
measurement function; and 2) Two wire connection, where the current source terminals also serve as voltage sense
probes as in the 2-wire Ohms measurement configuration. The first method eliminates lead resistance errors. One
application is in semiconductor diode characterization discussed in Component Testing above. See Current Source
Output for range details. Voltage compliance is limited to 4 V in both configurations.
Signametrics
40
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