Operator`s manual

Figure 4-2. AC and DC Current measurement connection.

4.2.1 Improving Current Measurements

hen making senW sitive DC current measurements, be sure to use the Relative function to zero out any residual

erro the appropriate DCI

mmended that whenever

ractical, higher current measurements be limited to in time. The lower two ranges of DC current may be effected

by relay contamination. If the measurements seem unstable or high, while in IDC measurement, apply between

20mA and 50mA DC to the current terminals and clean the K2 relay using the DMMCleanRelay(0, 2, 200). Repeat

this until the measurements are stable.

4.2.2 Low Level DC Current Measurements

For low-level current measurements use the V, Ω+ and V, Ω- terminals. Using the 33V DCV range, the SM2040

can measure very low currents. This hidden measurement function is facilitated by the DMM’s low leakage front-

end and a virtual 10.0MΩ input resistance. With a typical offset error of less than 100µV in this VDC range, it is

practical to measure down to 20pA. The maximum current value that can be measured has more to do with the

user’s acceptable burden voltage (the voltage drop across the 10.0MΩ shunt) then the DMM limitations. Assuming

a maximum burden voltage of 3.3V the maximum current level is 330ηA. This rage is well within leakage

measurements required in most semiconductor testing. It is also a very quite and stable. Since the DMM does not

have an explicit low current function, it is necessary to calculate the current which is equal to the measured voltage

divided by 10.0MΩ.

4.2.3 Extended DC Current Measurements (SM2044)

The leakage measurement function can also be used to measure low-level currents. Using a relatively high value

shunt resistor and setting the leakage test voltage to 0V allows measurements of super low level currents, without

any burden voltage. Read the leakage current section of the manual for more details.

rs of the SM2040. Disconnecting all terminals to the DMM and performing Relative in

range easily accomplish this. Using the S-Cal (DMMCalibrate()) prior to activating Relative will improve

accuracy further. Although the SM2040 family is designed to withstand up-to 2.5A indefinitely, be aware that

excessive heat may be generated when measuring higher AC or DC currents. If allowed to rise this heat may

dversely effect subsequent measurements. In consideration with this effect, it is recoa

Signametrics 26