PNI SENtral MandM - Manual (Page 39)

PNI Sensor Corporation Doc #1020129 revE
SENtral M&M Technical Datasheet Page 38
To measure average current consumption, simply touch either side of the 100 Ω
resistor with the voltmeter’s probe tips and measure the voltage drop. Convert to
current consumption using:

A = 10*mV, assuming a 100 Ω resistor.
It is possible to observe the current consumption waveform using an oscilloscope. In
this case, place a 100

F capacitor in parallel with the 100 Ω resistor. This reduces
the measurement bandwidth so the waveform can be better observed.
Note that SENtral’s bypass capacitors are electrically connected nearest the device
after the sense resistor or the voltage meter’s resistor. This will bandlimit the
measurement to ~1.5 kHz for a 100 Ω resistor. The onboard bypass capacitance
totals 1.1

F.
Method 2: Remove zero-ohm resistor and place ammeter in series.
This method is relatively straight forward to implement, as the probes are physically
soldered to the PCB. To help prevent damage to the PCB surface pads, PNI strongly
recommends implementing a strain relief for the wires.
Note that the burden voltage of a typical digital multimeter (ammeter) is ~100

V/

A,
or 100 Ω. PNI has tested such an ammeter in the Method 2 scenario and seen that it
does not affect operation. Also note that negative voltages produced by transient
currents are smoothed by the local bypass capacitors.
Also, it may be difficult to measure DC current using ammeters with very fast
measurement times due to the periodic wake/sleep cycles of SENtral. Consequently,
handheld DMMs with relatively long measurement integration times work well for
making average current measurement. Precision benchtop meters with an averaging
or smoothing filter also can work well.