Looking at all the field instruments distributed around a process unit, stop for a moment and remind yourself that there is a lot more going on inside those instruments’ transmitters than you tend to think of on a daily basis. Advanced instrumentation is amazingly sophisticated but often underutilized in many environments, but it doesn’t have to be that way. With a little clever connectivity, it can provide much more valuable data.
Connor Oberle describes how this can work in his article in the March 2019 issue of IIoT for Engineers, Extend Edge Data Gathering with Multivariable Instruments. He makes the point that there is lots of data locked into advanced instrumentation and it’s dying to get out.
A DP [flow meter] transmitter measures the pressure drop, and its electronics convert the pressure drop into a flow reading. This is the primary variable from the transmitter, but what other measurements are possible? Multivariable transmitters have additional sensors within a single transmitter. An additional pressure sensor is located within the transmitter module to measure the line pressure. Instead of simply knowing that the differential pressure is 3 psi, this additional measurement allows the pressure on the primary element’s upstream and downstream sides to be known. Additionally, multivariable transmitters can take readings from temperature sensors. These valid process readings can be used as individual values, without the need for separate pressure or temperature transmitters on the same line.
An example of the kind of DP flow meter Connor is describing is the Rosemount 3051SFP Integral Orifice Flow Meter. It is actually a cluster of sensors working together, constantly exchanging information to generate the most accurate primary reading, but also secondary, tertiary and more readings of other variables.
When it is possible to measure DP, line pressure and fluid temperature, these three values can be combined with measurements fed into the transmitter’s configuration. If plant personnel provide the fluid type, primary element configuration, and line size to the transmitter, a range of process measurements can be calculated, such as:
These measurements can be generated by one instrument with one primary output.
So why don’t more users take advantage of these capabilities? An excellent question and the answer depends on the operating environment and the sophistication of the device level networking system. If the DCS has dumb analog I/O, all that extra information is going to be stranded in the transmitter, with no way to get out. Connor discusses several possible solutions, so give the article a full reading. Ultimately, he suggests one as likely the most practical in the greatest number of situations.
Absent one of the sophisticated I/O approaches just mentioned, adding a WirelessHART adapter (or using a native WirelessHART transmitter) is arguably the best interface to get process data, whether simple or multivariable, into an IIoT environment. The adapter mounts on a transmitter housing and can send data to a WirelessHART gateway without disrupting the established wired connection to the host system. Since WirelessHART is digital, the gateway can convert it to Ethernet or other protocol such as Modbus RTU. The number of plants installing WirelessHART infrastructure has increased rapidly over recent years, so for many, it is a simple matter to add one more device to the network. Most HART-enabled instruments can be configured to prioritize variables as needed.
A WirelessHART adapter as suggested could be the Emerson Wireless 775 THUM Adapter, which retrofits onto existing HART devices, a category covering most instrumentation installed over the last 10 or even 15 years.
You can find more information like this and meet with other people looking at the same kinds of situations in the Emerson Exchange365 community. It’s a place where you can communicate and exchange information with experts and peers in all sorts of industries around the world. Look for the Flow, Pressure and Digital Transformation Groups and other specialty areas for suggestions and answers.
Posted by Deanna Johnson, Director Integrated Marketing Communications for Machine Automation Solutions
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