Section 4: Measure considerations
Model DMM7510 7½ Digit Graphical Sampling Multimeter Reference Manual
4-14
DMM7510-901-01 Rev. B / May 2015
Solutions
Possible solutions to address cable effects:
1. Add a second switch to engage the test current after the short is removed, as shown in the
following figure.
Figure 144: Cable effects solution
2. Set the DMM to a higher dry-circuit ohms range as the 10 K
Ω
range with 5
µ
A of I
test
current. The
cable effects are directly reduced with reduced I
test
current.
3. For the cable that connects HI and LO to the DUT, choose a cable with a very low characteristic
impedance so that the maximum DUT voltage is small.
4. Terminate the end of the cable with an RC snubber that is less than 1
Ω
in series with a parallel
10
µ
F and 1 M
Ω
, which maintains low voltage and a single damped response.
With offset compensation enabled and reading triggering halted, the idle test current of all dry-circuit
ranges is less than or equal to 10
µ
A. When the Model DMM7510 is in either of these setups, the
shorting switch across the DUT can be safely opened with minimal cable energy storage issues.
Offset-compensated ohm calculations
The presence of thermoelectric EMFs (V
EMF
) can adversely affect low-resistance measurement
accuracy. To overcome these offset voltages, you can use offset-compensated ohms if you are
making 4-wire resistance measurements on ranges up to 100 k
Ω
.
Instrument operations, including offset-compensated ohms, are performed on the input signal in a
sequential manner.
For a normal resistance measurement, the Model DMM7510 sources a current (I) and measures the
voltage (V). The resistance (R) is then calculated as (R=V/I) and the reading is displayed.
For offset-compensated ohms, two measurements are performed: one normal resistance
measurement, and one using the lowest current source setting.
