The new standard of sensor interface was born and set off a new wave of solutions

Some comments in the industry have overstated the demise of the IEEE1451 smart transmitter interface standard. The standard was shelved until developers started using the recently approved IEEE 1451.4 section. This part of the standard adds storage elements to make the sensor more intelligent, and it also adds self-identification through the Transmitter Electronic Data Sheets (TEDS). This easy method allows the transmitter spreadsheet to be used for a large number of existing analog sensor interfaces, adds plug-and-play functionality, and ensures accurate and economical solutions and applications. In short, P1451 is no longer "a solution to the problem" (P stands for the entire standard currently in submission).

This standard meets the long-felt expectations of manufacturers of small and medium-sized sensors and transmitters - seeking a universal sensor interface, but it has long assumed the historical burden of different networks, fieldbuses, protocols, and demands. The original concept of the 1451 standard was to allow space for the transmitter housing to be mounted on the drive, allowing the transmitter to be plugged into the P1451 driver, reducing the need for specialized drives. It is said that 90% to 95% of the previous software development time can be saved. .

The historical background 1451 was initiated in 1994 by the Institute of Electrical and Electronics Engineers (IEEE) Instrumentation and Measurement Branch and the National Institute of Standards and Technology (NIST) in the hope of addressing the problems of traditional sensor integration with standard communication interfaces. At present, P1451 has grown to have 7 working groups, of which 4 are officially approved.

Recently, the P1451.3 working group has defined standards for clustered sensor applications and ensuring high-speed, simultaneous data transmission. At the same time, the P1451.4 working group completed the application of analog transmitters for mixed-mode communications, such as digital spreadsheets and analog signals.

About two years ago, National Instruments reported that it was aware of the potential value of 1451.4 and began working more actively with the IEEE working group. NI's incentives and IEEE approvals have been the driving force behind the 1451.4 recovery.

The development of 1451.4 adds plug-and-play functionality to analog transmitters that can be added to the network of digital instruments and measurement systems. IEEE1451.4 currently has a good opportunity to accelerate the application of networked sensors by simplifying the installation of transmitters, the construction of networks, and the maintenance and updating of systems. 1451.4 The above objectives are being achieved through the establishment of a universal system that requires the identification, identification, interface, and use of signals from analog sensors.

1451.4 Working group deputy chairman, David Potter, National Instrument Manager of the United States, explained that 1451.4 is a practical technical standard that makes the transmitter spreadsheet compatible with analog measurements. "Because of the added self-identification capability in the transmitter analog interface, this standard has the potential to make any measurement system, analog or digital, easier to install, configure and maintain. When the sensor is connected to a data acquisition device or any dashboard, There will be a lot of installation area, filtering and other parameters. If this information is already stored on a memory chip, then you can install and calibrate it automatically."

The 1451.4 standard also utilizes electrically erasable, programmable, read-only memory chips (EEPROMs) embedded in sensors to enable the storage and communication of plug-and-play functional details. Manufacturers can get chip identifiers from the Internet. A complete transmitter spreadsheet may contain the type identification and attribute content of a specific type of sensor, such as accelerometers, microphones, strain gauges, thermocouples, and other types of sensors. Transmitter spreadsheets can also include all sensor calibration data.

The requirement for a specific sensor is that the template description file should be given and published on the website. This standard takes into account the fact that some existing sensors cannot embed memories such as EEPROM, so a virtual transmitter spreadsheet is provided on the Internet. National Instruments and his partners provide a huge library of virtual transmitter spreadsheets that can be found at the Web site. Download com/sensors for free. As part of the National Instruments Partner Program, approximately 25 companies currently provide sensors that meet the 1451.4 standard.

Seymour at ISA 2004 Showcases How Watlow's Infosense-P Plug-and-Play Thermocouples, RTDs, and Thermistors Work with 1451.4-Compliant Chip and Transmitter Spreadsheets to Calibrate One A typical "coathanger" makes it more accurate than traditional temperature sensors.

Watlow's "coat hangers"

For test and measurement users, the 1451.4 standard can greatly improve the accuracy of thermocouples. For example, a typical J-type thermocouple consists of two metals of different grades and relative accuracy. However, Watlow recently discovered that adding a single-line memory of 1451.4 to the thermocouple it produces improves the calibration performance and the linearity of the curve. The measurement error is reduced by a factor of three from 1.5°C to 0.5°C, making it more accurate than the Thermocouple of the American National Standards Organization. For example, a typical K-type thermocouple usually uses an uncertainty of ±2.6°C at 600°C. But by adding smart sensors and better raw materials that meet the 1451.4 standard, according to Chris Seymour, strategic marketing manager at Watlow, the uncertainty at 600°C can be reduced to 0.6°C. At the same time, he added that an A-class thermal resistance (RTD) typically has an uncertainty of ±1.4°C at 600°C, whereas the 1451.4's conversion to a smart thermal resistance can be as small as 0.2°C.

Murphy demonstrates how Watlow's Infosense-P plug-and-play thermocouples, RTDs, and thermistors work with the 1451.4-compliant chip and transmitter spreadsheet to calibrate a ISA 2004 event. A typical "coathanger" makes it more accurate than traditional temperature sensors.

“We mainly supply OEMs, which require precision and repeatability. They had to buy sensors with an accuracy range of 0.5% to 1.0% before, and now we can store all the calibration information in one memory.”, Seymour Say. “We can now understand the working status of a sensor in real time, because the digital components in it can tell us the operating status of its analog side. In this case, our OEM customers can produce and work at higher temperatures than Thermal resistance technology is more accurate than thermocouples, which are much more expensive."

Seymour added that using a chip that meets the 1451.4 standard means that Watlow can also use new hybrid materials such as superalloys in its thermocouples for better accuracy, longer life, and lower temperature drift. Now, all the voltage/resistance data sheets in the chip tell the instrument what type of sensor it may be. “In the past, users had to buy calibration sheets, but they were easily discarded. Now that you have a transmitter spreadsheet, it is impossible to separate the information from the chips,” Seymour added. “Also, the initial criteria was that the sensors had to run linearly, and the changes had to be linear because all the instruments were analog. Now that we have digital electronics, we can track and record any functions we want, including collecting relevant information. Future sensor operating fault data".