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Measuring Ultra-Low Power in Wireless

Sensor Node Applications Using the

Model DMM7510 7½-Digit Graphical

Sampling Multimeter

Introduction

The future of the Internet or the Internet of Things (IoT) is

an interconnection of uniquely identifiable embedded devices

often referred as IoT smart devices and sensors. A large

number of sensor nodes each capable of sensing and wireless

communication installed in an area of interest makes a wireless

sensor network. Billions of smart sensors push data to the IoT

through diverse applications, including home security systems;

lighting and HVAC control; utility monitoring; industrial control

and automation; bridge, railway, traffic light monitoring; and

various other infrastructure and environmental uses. Despite

the wide difference in applications, these sensor nodes share

architecture similar to wireless IoT smart devices, such as those

used in the medical, health, and fitness domains.

One of the most common challenges in all sensor node

design is power management. Wireless sensor nodes are often

placed in hard-to-reach locations where sourcing from mains

power is either inconvenient or impossible. Designers need

to closely examine the power consumption associated with

different operational states of the microcontroller (MCU) and

the transceiver of the wireless sensor node. In a typical sensor

node application, a node might sit idle for long periods of time

between peak periods of activity for sensor data acquisition and

wireless transmission. In other words, the power profile consists

of active peaks, that are represented by tens of milliamps at

maximum transmit or receive power, and long idle periods,

that are characterized by quiescent current as low as tens

of nanoamps.

Power = I × V

Energy = I × V × Time

Until recently, no single instrument offered the combination

of low current measurement range, resolution, and speed

capability necessary for these applications. The Keithley Model

DMM7510 7½-Digit Graphical Sampling Multimeter will fulfill

this need. The Model DMM7510 has an 18-bit sampling A-to-D

converter dedicated for digitizing current and voltage at 1Mega-

sample per second. The digitizing functions cover the same

measurement ranges as the DMM’s traditional DC voltage

and current functions. In other words, the instrument offers

exceptional current measurement capability from 100pA to 10A

with a 100kHz analog bandwidth that is suitable for both deep

sleep as well as active current measurements. Although voltage

is typically regulated in these applications, the Model DMM7510

is also capable of digitizing voltage from 1µV to 1000V and has

a higher analog bandwidth of 600kHz. Combining the advanced

waveform triggering mechanism, such as edge triggering, pulse

triggering, and window triggering, you can easily capture, view,

and interact with these dynamic signals on the Model DMM7510’s

multi-touch display.

This application note provides an overview on how to

characterize the ultra-low power consumption of a typical

wireless sensor node application on the front panel of the

Keithley Model DMM7510.

Evaluate a Single Current Pulse Profile

An accurate capture of the current waveform is critical for power

consumption calculation and can be easily accomplished on the

Model DMM7510. The first step is identifying a single trigger

event associated with the current pulse waveform of interest.

You can then use the built-in analog edge triggering mechanism

on the Graph user interface to set up the trigger span, trigger

slope, trigger level, trigger position, and sampling rate. With only

a handful of keystrokes to establish these acquisition criteria,

you can quickly view the desired waveform on the DMM’s

graphical display.

Figure 1

illustrates a typical multi-level active mode current

pulse captured by the Model DMM7510. The active mode

typically contains current levels as high as tens of milliamps.

These multiple current levels represent events such as start-up

and shut-down sequences, transmit and receive modes, sensor

data conversion, etc.

Figure 1. Example multi-level active mode current pulse proﬁle.

Table 1

summarizes the acquisition criteria involved in

capturing the waveform in

Figure 1

. With the exception of the

trigger mechanism configuration, which is only available when

the measurement function is set to Digitize Current, you are not

required to follow the exact sequence of operations listed in

the table.

Application Note

Se ries

Summary of content (4 pages)

PAGE 1
Application Note Series Measuring Ultra-Low Power in Wireless Sensor Node Applications Using the Model DMM7510 7½-Digit Graphical Sampling Multimeter Introduction The future of the Internet or the Internet of Things (IoT) is an interconnection of uniquely identifiable embedded devices often referred as IoT smart devices and sensors. A large number of sensor nodes each capable of sensing and wireless communication installed in an area of interest makes a wireless sensor network.
PAGE 2
Table 1. Configurations for Edge Triggered Digitize Current Waveform Configure measurement function Push the HOME key on the front display. On the FUNCTIONS swipe screen, select Digi I to select the Digitize Current function. Push the Range button to select 100mA range. Swipe to display the SETTINGS swipe screen. Set the Sample Rate to 1,000,000.
PAGE 3
levels often ranging from tens of microamps to as low as tens of nanoamps. Figure 3 is an example of a multi-level idle mode current pulse waveform captured on the 100µA range. The Model DMM7510 is capable of resolving current below a few microamps. All readings and timestamps are easily accessible through the Reading Table under the main MENU. See Figure 4. To save these readings to a thumbdrive, insert a USB thumbdrive in the USB port on the front panel. Press the MENU key.
PAGE 4
Figure 7. Zooming into a current pulse from a large acquisition period. 1µA. However, the effective resolution will be tens of microamps. Refer to the instrument specifications from Keithley’s website (www.keithley.com) for detailed accuracy information for different current and voltage ranges. Conclusion The Model DMM7510 is a must-have instrument for analyzing ultra-low power consumption in wireless sensor nodes and IoT smart device applications.