Internet of Things is a leading buzzword these days in the technology world. Most of the devices used to create the IoT (Internet of Things) work on small batteries. The measurement of energy consumption of these IoT devices is a difficult task due to the dynamic nature of the current consumption. Developers often need to use multiple instruments and hand calculations to arrive at an estimate of the energy consumption. To solve these problems, the ZS1100A Power Meter has been designed. This tool can plot the current consumption vs time very accurately and in great detail, which can be used along with the battery model to estimate the overall battery life. It has been created by engineers for engineers.

ZS1100A Power Meter - Complete Kit:

along with a power supply, two banana-to-alligator clip cables, eight jumper wires for the front-facing I/O, a USB cable, a flash drive with software, and a quick start guide.

Why do we need another energy meter?

The power consumption of IoT devices follow a peculiar pattern which is difficult to measure using traditional equipment. The main reasons for this are listed below:

High Dynamic Range: An IoT device would consume a few μA in sleep state and few hundred mA in its transmit state, depending on the radio. Thus, the current waveform has a very high dynamic range spanning almost 6 decades.

High Bandwidth: The current drawn by an IoT device can change from few mA to hundreds of mA in couple of micro-seconds. Thus, the frequency content of these current waveforms is well over few 100 KHz.

Long Profile Times: It is not uncommon for IoT devices to have a typical profile which can last for several tens of minutes to 1 hour. They may perform intermittent wake-ups during this time for some misc activities, and hence these also need to be recorded. For accurate power analysis, complete capture of the profile is needed

Drawbacks of Popular Measurement Methods

Multimeter: Most multimeters use range switching to achieve high dynamic range. While measuring the current, they introduce series resistor and measure the voltage across it. While measuring μA currents, the multimeter would add a few Ωs (may be kΩs) of resistance in series. If the IoT device performs a wake-up during this state, the drop across the high resistor can cause the device to trip and cause system reset. Most multimeters made for this application can record profiles for only few minutes. An IoT current profile can last several tens of minutes and hence the software on the IoT device may need to be modified to account for the limited capture time. Most multimeters do not have a full function GUI to measure various pulse parameters. The multimeters with digitizer options are expensive with retail costs starting at five thousand dollars, and often significantly higher.

Oscilloscope: Using a scope with a current probe is good enough to measure higher currents in idle and transmission modes. The sleep currents, which are of the order of few μA, cannot be measured with this due to the limited dynamic range. It can either measure high currents or low currents at a time. Most scopes use an 8- to 12-bit ADC and this limits the overall dynamic range. The capture length limits apply to most scopes and the overall solution is very expensive - at least few thousand dollars for the probe and tens of thousands for the scope.

These limitations call for a new approach : ZS1100A Power Meter

Demo Wi-Fi Power Profile:

The current profile of an ESP8266 Wi-Fi module is captured here. The module wakes up from sleep using an internal timer and GPIO toggling the RESET pin. The GPIO is captured in the bottom chart. The current rises from 16 μA to few mA in couple of ms. Then it reaches tens of mA and then few hundred mA during the calibration. All of these states are captured in a single range with ZS1100A. This demonstrates the dynamic range, bandwidth, capture length and digital sync feature of the tool. Note how the output voltage remains constant throughout this variation.

Measurement Specifications:

Parameter	Specification	Notes
Output Voltage Range	0 to 6 V	Programmable in 10 mV steps
Output Voltage Accuracy	Error of 5 mV max	Measured with 500 mA load
Current Measurement Range	-0.5 A to 1.5 A (linear range)
Current Measurement Accuracy	1% of measured value ± 0.2 μA	After one time self calibration
Current Measurement Resolution	< 0.1 μA
Max Output Current	1 A constant current	Vout = 5.0 V
	2 A with 10% duty	Measured with 100 ms pulse for every 1 second
Load Regulation	<0.1%	0 to 1.5 A
Measurement Bandwidth	300 KHz	3 dB bandwidth
Step Response	2 μS	10% to 90% of full range
Current Sampling Rate	1 MHz
Sampling Jitter	10 ps	RMS jitter
Voltage Sampling Rate	Once in every 20 ms
Digital Capture	6 bits at 1 MSPS
Maximum Capture Length	Tested up to 24 hrs	Limited only by the free space on the HDD
Error Rate	< 1e-12	Less than 1 error in 10^12 samples
		Or less than one sample error in 24 hours

Product Specifications:

Computer Interfacing: USB 2.0, Type-B connection
Free GUI with waveform analysis tools (Windows-only for now)
Data can be exported to sigrok/PulseView for UART, SPI, I²C protocol analysis
Data can be exported as ASCII in XML
Excellent data compression rates - 24 hours of data takes ~10 GB

I/O: Front-facing pins with standard (2.54 mm/.1") pitch in a 2x5 configuration
- 6 digital inputs
  - Function as a logic analyzer capturing at 1 MHz
  - Voltage range of 1.8 to 5 V
  - Input impedence of 10 pF || 100 kΩ
  - 4 have 100 kΩ pull-down resistors
  - 2 have 100 kΩ pull-up resistors to VCC
- 2 GND pins (shorted with the power supply ground)
- 1 VCC pin
- 1 CLK output at 1 MHz, 3.3 V, driving a load of 30 pF || 100 kΩ
- 8 jumper wires included with purchase