Whitepaper #04: Cost Effective Embedded Power Monitor

Posted & filed under Whitepapers.

Kevin Harris
Marketing Manager
TEAL Electronics

Abstract

Embedding an Ethernet connected web-based low-cost power monitor into a permanently installed Original Equipment Manufacturer’s (OEM) 3-phase power subsystem gives the user the ability to monitor their sites 24x7x365. As compared to the more traditional temporary power monitoring for OEMs, having a monitor permanently installed at each site can help prevent costly and repetitive site problems by identifying if the AC power is related to a specific site problem anytime. To make an embedded power monitor solution feasible, the device must be low cost, and to capture typical power quality events, it must be high performance.

TEAL Electronics is introducing the TEALwatch® power monitor, a low-cost embedded power monitor utilizing a web based interface for remote monitoring capability. The TEALwatch® is designed to be integrated into a 3-phase power subsystem, monitoring the mains voltage at the power entry point for the OEM equipment such as Semiconductor Automated Test or Medical Imaging equipment. The monitoring interface is Ethernet 10base-T, enabling remote monitoring with a simple web browser from any Internet connected PC, with no special software required. The TEALwatch® features programmable triggering parameters and has built-in non-volatile storage for multiple waveforms captured on triggered events with 128 samples per cycle resolution.

Introduction

Over the past several years, TEAL has integrated various power monitors into our OEM power subsystems for several customers that desired to have monitoring capability 24x7x365. The advantages of having a permanently installed power monitor at each site are that the OEM customer can correlate site issues with power issues to identify or eliminate the root cause of a site issue at anytime. With a temporary monitor installed, you often miss events or are simply too late to capture critical information. The primary issue in each of these cases was simply that the cost for the monitor option was just too high, often between $1,500 and $3,500 for each monitor. The added cost for the optional monitor often approached the cost for the rest of the power subsystem. With the ability to rent a monitor for less than $1,000 (albeit as a temporary monitor), along with the ever increasing cost pressures on suppliers, most customers are unwilling to pay the added premium for a permanently install solution.

For some time, TEAL investigated low cost options from many of the power monitor manufacturers, and none could meet our cost (less than $500) and specification/performance targets. For these reasons, TEAL undertook a project to develop our own power monitor that meets our, and most of our customer’s, criteria. The result of this project is the TEALwatch® power monitor.

The TEALwatch® is essentially a Linux-based web-server in a box with an outboard power supply with an isolated voltage divider to provide the input connections. It was developed by TEAL Electronics specifically as an extremely cost-effective power monitor device to be offered as an option on TEAL 3-phase power subsystems.

Having a TEALwatch® connected to the output of the TEAL power subsystem to monitor the input to the OEM customer’s critical equipment provides a proactive diagnostic tool for power quality issues that will decrease service costs for each site or installation by enabling remote diagnostics of power related events.

Design Optimization

The design of the TEALwatch® power monitor was optimized for cost versus performance. Our aggressive cost targets were the primary project drivers, but we had several pre-requisites for performance that had to be met for the project to move forward. First, the sampling rate had to be high enough to capture most typical transient events that can cause damage or disruption to the equipment being powered. Second, it had to be able to be triggered by both transient events and longer-term RMS type events, as both are important power quality areas. Third, it had to be able to store recorded waveform events for further analysis. Fourth, it had to have a simple and easy to use remotely accessible interface that did not require a local display to be installed (as local displays add cost and typically would not be useful for our customer base). Fifth, the hardware pipeline design must be for 8 channels of data (3 voltage + 3 current + 2 additional). Sixth, it had to be robust enough to continue monitoring and accurately capturing data, even when the power to it’s own power supply is seeing a large power event. Lastly, the design is for an embedded solution, not a stand-alone power monitor device.

To facilitate the design of the Ethernet based web browser interface, a microprocessor based hardware design was implemented utilizing a Linux based web-server hardware design, with TEAL designing the input and output functions and interfaces. The processor that was selected enabled a sampling rate of 128 samples per cycle for 6 of the 8 channels (for voltage and current), with a more limited sampling on the other 2 channels. This sampling rate is high enough to at least capture a waveform excursion with a transient event, even with a high frequency transient event. The microprocessor has the ability to process the data to monitor longer term RMS type data as well as perform data trending. This addresses our first two pre-requisites.

A reasonable amount of both dynamic Random Access Memory (RAM) as well as Non-Volatile (N-V) RAM was provided to allow for multiple full waveform storage and many summary events in N-V RAM as well as many more full waveforms in dynamic RAM. Data stored in N-V RAM can be retrieved even after a full power outage. The waveforms and trend data that are stored in the TEALwatch® are easily downloaded by simply clicking on the download button and directing the file to the location of your choice when you are connected via the standard Ethernet connector. Different types of power quality signatures, waveforms, and events used for triggering have been identified, (1) (2) (3), and many of the common types are used to trigger events in the TEALwatch® monitor. Events that can trigger the TEALwatch® include positive and negative sub-cycle waveform excursions (transients), waveform distortion, voltage surges and sags (longer-term RMS type events), phase rotation, phase-to-phase balance, and frequency deviations. In addition, trend data is recorded at regular intervals. These items address our third and fourth pre-requisite.

The hardware pipeline design includes 8 channels for monitoring and the power supply – voltage divider interface is robustly filtered to both protect the data lines and to ride-through most power disturbances without dropping out. These items address the fifth and sixth pre-requisites.

Lastly, the TEALwatch® design is specifically an embedded design. The TEALwatch® hardware consists of 2 pieces, the web-server section and the power supply – voltage divider section. The web-server section is a small box with the external Ethernet connector for network connection. The power supply – voltage divider section is an open frame PCB that is mounted near the web-server box inside a power subsystem.

All the primary pre-requisites were met, as well as the aggressive cost target. TEAL expects to be able to include the TEALwatch® power monitor as a power subsystem option for under $700 in OEM quantities, with list prices higher of course.

User Interface

The real innovation for the TEALwatch® power monitor is the extremely easy to use web browser interface. No special software is required for the interface, only standard Internet Explorer or Netscape browsers. The connection is via a standard 10base-T Ethernet connector, and direct or router based connections can be used. Network connection of the TEALwatch® allows 24x7x365 monitoring from anywhere.

The TEALwatch® power monitor main menu bar layout consists of 6 tabs: HOME, STATUS, SETUP, N/W ADMIN, ADVANCED, and HELP. The main page for displaying data is the STATUS page shown below.

TEALwatch® user interface

The main STATUS page for the TEALwatch® power monitor user interface, available from virtually any Internet connected PC with a web browser. The STATUS page displays live data as well as trigger events that have been captured with full data sets available for easy download and viewing using Microsoft™ Excel or a similar program.

TEALwatch® event trigger screen

The TEALwatch® STATUS page displays the data captured as full waveform data in Non-Volatile
(N-V) RAM (shown in green) as well as additional full waveform data that is not buffered in N-V RAM although the summary data for each event is (shown in yellow). Simply clicking on the DOWNLOAD button downloads that individual file, which can then be opened and analyzed using Microsoft™ Excel or a similar program.

TEALwatch® setup access screen

Clicking on the SETUP, N/W ADMIN, or ADVANCED tabs on the menu bar will invoke the TEALwatch® login and password screen. Users without password access will only be able to view and download data, but cannot change any settings. Your Administrator via the ADVANCED tab page will control passwords.

TEALwatch® setup screen

Screenshot showing the TEALwatch® SETUP screen. The first option is to load a complete set of global defaults which are pre-set parameters that can be pre-defined at the factory for specific applications to optimize event capture for a specific customer or application. Programming any of the set points is simple point and click. Phase Rotation monitoring is adjustable, and Trend Data logging and sampling is also adjustable.

Setting sub-cycle triggers

Screenshot showing the password protected Sub-Cycle Event Trigger parameter section of the setup screen for the TEALwatch® power monitor. You can even re-name the triggered event names to ensure that everyone in your organization uses the same terminology.

Setting RMS, Phase and frequency triggers

Screenshot showing the password protected TEALwatch® RMS Event Trigger and Phase & Frequency Event Trigger parameter section of the setup screen. You can even re-name the triggered event names to ensure that everyone in your organization uses the same terminology.

Network administration screen

Sample screenshot showing the N/W ADMIN screen feature of the TEALwatch®. This password-protected screen allows the customization of the URL address for the TEALwatch®.

Setting administrator passwords and system clock

Sample screenshot in the ADVANCED tab showing the Login/Password Administration screen feature of the TEALwatch®. Three levels of password protected Administration exist. First, the PM Administrator can modify basic trigger point settings and other basic setup functions (under the SETUP tab). Second, the Network Administrator can modify the network settings and URL address (under the N/W ADMIN tab). Third, the Master Administrator has the rights of both the Network Administrator and the PM Administrator as well as other admin rights (under the ADVANCED tab shown above).

Summary

The TEALwatch® is a very cost effective power monitor designed as an embedded option in a TEAL power subsystem. The TEALwatch® monitors the AC voltage and utilizes a very easy to use interface via any standard web browser. No special software is required, only the connection of the TEALwatch® with a standard Ethernet (10base-T) cable to an Internet accessible network or directly to a PC or laptop.

A TEALwatch® power monitor installed at each site can help prevent costly and repetitive site problems by helping to correlate if the AC power is related to a specific site issue. Monitoring power disturbances 24x7x365 at all installation sites from anywhere in the world will significantly reduce overall maintenance costs by enabling the user to remotely diagnose power-related issues prior to a service call. The TEALwatch® can also help to identify any additional power conditioning that may be required for a specific site, such as active voltage regulation or a full UPS system, on a site-by-site basis. This will save the OEM customer money by only applying the more expensive power quality solutions to the specific sites that require it.

The TEALwatch® will be available as an option on TEAL three phase power subsystems this fall. It will also be available as a field installable retrofit kit for many TEAL power subsystems already installed to enable our customer base to monitor sites already operating.

The TEALwatch® features include a 10-bit resolution and 128 samples per cycle, with programmable settings for triggering on short-term transient events as well as long-term RMS events. Multiple triggered events are stored in non-volatile memory as well as summary information for several hundred past events, and can be easily downloaded to your PC for viewing and analysis.

 Acknowledgements

The author would like to thank Chris Mathewson, Randy Redding, and Gary Jasinski of TEAL Electronics and Jude Russell of Powerlines for their contributions to this paper.

References

1. Handbook of Power Signatures, Alexander McEachern, Basic Measuring Instruments, 1988.
2. The Dranetz Field Handbook for Power Quality Analysis, David Kreiss, Dranetz Technologies, 1991.
3. The Evolution of Power Quality Data Acquisition Systems – Triggering to Capture Power Quality Events, Dan Carnovale, Dan Ellis, and David Iacovino, Proceedings of the 14th International Power Quality Conference, 2001, pages 395-404.

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Embedded Monitor (PDF)

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