Plug & Play Smart Sensors - Seminar Report

Introduction

Most sensors put out some sort of analog signal a voltage, current, or resistance that varies in a fixed relationship to a physical parameter. Instrumentation that converts the signal to engineering units must know a few things about what parameters to expect from the sensor. That's because full-scale range, sensitivity, connection schemes, and other factors all vary greatly from one kind of sensor to another. The end result is that it takes some effort to match up sensors with monitoring electronics. This configuration process may be no big deal when there are only a few sensors involved. But it can be problematic when gangs of sensors get wired into multichannel measurement systems.

Sensor

A sensor is a device that measures a physical attribute or a physical event. It outputs a functional reading of that measurement as an electrical, optical or digital signal. That signal is data that can be transformed by other devices into information. The information can be used by either intelligent devices or monitoring individuals to make intelligent decisions and maintain or change a course of action.

Smart Sensors

A smart sensor is simply one that handles its own acquisition and conversion of data into a calibrated result in the units of the physical attribute being measured. For example, a traditional thermocouple simply provided an analog voltage output. The voltmeter was responsible for taking this voltage and transforming it into a meaningful temperature measurement through a set of fairly complex algorithms as well as an analog to digital acquisition. A smart sensor would do all that internally and simply provide a temperature number as data. Smart sensors do not make judgments on the data collected unless that data goes out of range for the sensor.

IEEE 1451.4 defines a relatively simple, straightforward mechanism for adding smart, plug and play capabilities to traditional analog sensors. Without adding any new hardware to the system, these plug and play sensors can bring real, immediate benefits in ease of use and productivity to any measurement and automation system that uses sensors. Additionally, IEEE 1451.4 defines a standard framework for sensor description, embodied specifically in the TEDS, which can scale from today's traditional analog sensors to tomorrow's smart networked sensors.

Two factors have promoted widespread adoption of plug-and-play sensors: the IEEE P1451.4 Smart Transducer Interface draft standard and the Internet. IEEE P1451.4 is a proposed standard for self-describing analog sensors using standardized Transducer Electronic Data Sheets (TEDS). The Internet can bring the plug-and-play concept to legacy sensors and systems via distribution of so-called virtual TEDS. The next generation of measurement and automation systems will use these concepts to become even more automated, robust, and smarter.

The 1451.4 standard calls for a mixed-mode interface. This is essentially the digital and analog signals being transferred back and forth between the signal conditioning hardware and the sensor, making it more compatible with the legacy sensors in place. The first three versions called for sending only digital data back to the computer. The next version of the standard being drafted now is P1451.5, which adds wireless capability to sensors. Right now, the P1451.4 is still a proposed standard which is expected to be ratified and issued by soon.

Plug-and-play sensors address the labor involved in connection and configuration. Based on open industry standards, plug-and-play sensors incorporate ways of automatically identifying themselves. Benefits include quicker, more automated system setup; better diagnostics; less downtime for sensor repair and replacement; and an easier time keeping track of sensors themselves as well as the data they generate.

The IEEE P1451.4 plug-and-play sensor concept appears to be one of those rare technologies whose strength and value come from its simplicity and focus. Although it doesn't fit many of the typical definitions of a smart sensor, it does provide real, tangible benefits in a way that builds on, not replaces, existing systems and technologies.

UM6 Orientation Sensor

Description

The UM6 Ultra-Miniature Orientation Sensor combines sensor measurements from rate gyros, accelerometers, and magnetic sensors to measure orientation at 500 Hz. The UM6 also has the capability to interface with external GPS modules to provide position, velocity, course, and speed information. Communication with the UM6 is performed over either a TTL (3.3V) UART or a SPI bus.

The UM6 was designed specifically to be easy to use - an external enclosure protects sensitive electronics, and connectors make it easy to interface with the sensor without making solder connections to the sensor itself. Two 12-pin female connectors on the underside of the UM6 allow the sensor to be plugged directly into a host system.

The UM6 Serial Breakout Board provides everything needed to connect the UM6 to a PC, configure the sensor, perform basic calibration, and display data in real-time.

Outputs (User-Selectable)

• GPS position, heading, and velocity (with connected GPS)
• GPS position in meters from customizable home location
• Euler Angles
• Quaternions
• Raw gyro, accel, and mag data
• Processed sensor data (scale factors applied, biases removed)
• Attitude estimate covariance

Features

• Supports GPS connectivity and data parsing
• GPS position can be reported in meters from user-customizable home position
• Automatic gyro bias calibration (initiated by user command)
• Adjustable output rates (20 Hz - 300 Hz) and baud rate (up to 115200 baud)
• Open-source firmware with free development tools
• Open-source PC software for data visualization, calibration, and AHRS configuration

Specifications

• States updated internally at 500 Hz
• Better than 2 degree pitch and roll angle accuracy1
• Better than 5 degree yaw angle accuracy
• +5V input voltage, 3.3V logic level (5V tolerant)
• +/- 2000 °/s maximum measurable rotation rates
• +/- 2g maximum measurable acceleration

Resources

DATASHEETS AND APPLICATION NOTES

UM6 Datasheet

AN-1003 - Getting Started with the UM6 Orientation Sensor

AN-1002 - Reprogramming the Firmware on the UM6 and the UM6-LT

OTHER

Serial Interface Software v2.2.0 - Windows Installer

Latest UM6 Firmware .hex file and firmware definition (UM2B)

SOURCE CODE

UM6 Firmware

The UM6 firmware source is available from Sourceforge and can be checked out using SVN.

Serial Interface Software

The Serial Interface Software source code is available from Sourceforge and can be checked out using SVN.

What are Plug & Play Smart Sensors?

A Plug & Play Smart Sensor is a Sensor that is compliant to the IEEE 1451.4 Standard. TEDS, or Transducer Electronic Data Sheet, is a set of electronic data in a standardized format defined within the IEEE 1451.4 standard. This data specifies what type of sensor is present, describes its interface, and gives technical information such as sensitivity, bridge type, excitation, etc. This information is stored in an EEPROM chip attached to a sensor. By having this chip, the sensor can identify and describe itself to the network and or Smart Load Cell Meter, thereby easing automatic system configuration. With TEDS you will save time. You can interchange any TEDS senson without having to program or calibrate the instrument. It's truly Plug & Play.

Benefits that can be experienced now include:

Simplified troubleshooting

Reduced safety risks. It is no longer necessary to

"climb on machines" for connection verification

Reduced costs for set-up and tear-down

No recalibration is needed when replacing sensors

The data acquisition system can recalibrate itself

Advantages that will be available in the future include:

Integration with wireless transceivers

Elimination of large lengths of analog wiring

Reduced installation, maintenance and upgrade

costs of measurement and control systems

The opportunity to add intelligence to sensors

What is Virtual TEDS?

Virtual TEDS is an online library of data sheets developed by National Instruments (www.ni.com) that contain the same information that would be found in an EEPROM TEDS, but exist for sensors not containing the EEPROM. This would define Plug & Play capability for legacy / non-TEDS sensors. As a National Instruments Plug & Play Sensor Partner and a National Instruments Alliance Member, Transducer Techniques has contributed the data for all its sensors to the Virtual TEDS database.