Figure 4-10. Anatomy of a measurement
4.6 RTD Temperature Measurement (SMU2064)
For temperature measurements, the SMU2064 measure and linearize RTDs. 4-wire RTD can be used by
selecting the appropriate RTD type. Any ice temperature resistance between 25
and 10 k
can be set
for the platinum type RTDs. Copper RTDs can have ice temperature resistance values of 5
to 200
.
The highest accuracy is obtained from 4-wire devices, since this method eliminates the error introduced
by the resistance of the test leads. The connection configuration for RTDs is identical to 4-wire Ohms.
4.7 Internal Temperature (SMU2064)
A special on board temperature sensor allows monitoring of the DMM’s internal temperature. This
provides the means to determine when to run the self-calibration function (S-Cal) for the DMM, as well
as predicting the performance of the DMM under different operating temperatures. When used properly,
this internal temperature measurement can enhance the accuracy and stability of various measurements. It
also allows monitoring of the PC internal temperature, which is important for checking other instruments
in a PC-based test system. To use this function use
DMMSetFunction()
with the
TEMP
_LCL (43)
parameter, followed by a read function (
DMMRead, DMMReadNorm or DMMReadStr
).
4.8 Diode Characterization
The Diode measurement function is used for characterizing semiconductor part types. This function is
designed to display a semiconductor device’s forward or reverse voltage. The DMM forces a current and
measures voltage drop. The available source currents for diode I/V characterization include five DC
current values, 100
A, 1
A, 10
A, 100
A and 1 mA. The SMU2064 have an additional 10 mA range.
The SMU2064 also has a variable current source that may be used concurrently with DCV measurement
(see “Source Current / Measure Voltage”). This allows a variable current from 10
A to 12.5 mA. The
maximum diode voltage compliance is approximately4 V.
Applications include I/V characteristics of Diodes, LEDs, Low voltage Zener diodes, Band Gap devices,
as well as IC
testing and polarity checking. Typical current level uncertainty for diode measurements is
1%, and typical voltage uncertainty is 0.02%.
4.9 Capacitance Measurement, Charge Balance method
The DMMs measure capacitance using a differential charge balance method, where variable currents are
utilized to stimulate a dV/dt response. This method is very fast, and will adapt for the best speed and
accuracy at a given range and capacitance value. With the exception of the 1,200 pF range, which
measures down to 0pf, all ranges have a reading span from 5% of range to full scale. Capacitance values
less than 5% of the selected range indicate zero. Since some large value electrolytic capacitors have
significant inductance, as well as leakage and series resistance, the Auto ranging function may not be
practical. Because Capacitance measurement is sensitive to noise, keep the measurement leads away from
noise sources such as computer monitors. For best measurement accuracy at low capacitance values, zero
the DMM using the ‘Relative’ while in the 1,200 pF range. The effect of the cable quality, stability and
total capacitance is profound particularly on low value capacitors. For testing surface mount parts, use the
optional Signametrics SMT Tweeter probes. You may trade off accuracy for speed in the SMU2064 by
using the
DMMSetCapsAveSamp()
function. See figure 4-11 for connection.
Signametrics
44
