PVTs use diagnostics, go digital, deliver multiple readings
Trends in Process Variable Transmitters Diagnostic capabilities Digital protocols Faster communication ONLINE See this product focus at www.controleng.com for additional information. Process variable transmitters (PVTs) perform a type of dance that goes on between various processes and the transmitter moving information to the end-user.
Trends in Process Variable Transmitters
See this product focus at www.controleng.com for additional information.
Process variable transmitters (PVTs) perform a type of dance that goes on between various processes and the transmitter moving information to the end-user. Users have seen this dance for over four decades. Partners may have changed, but the basic technique of one protocol has remained consistent.
Ola Wesstrom, pressure product manager for Endress+Hauser (Greenwood, Ind.), says, ‘After 30 years, 4-20 mA still has a strong hold. Unless something revolutionary happens, I don’t see indication of it going away at least for another 10 years.’
And it plays well with others, Mr. Wesstrom adds; ‘Everything recognizes 4-20 mA.’
Jonathan Rowe, pressure product manager, The Foxboro Company (Foxboro, Mass.), says, ‘When ‘smart’ and ‘intelligent’ transmitters were developed, they took advantage of the ability to put pulses on the 4-20 mA signal, either while the 4-20 mA signal was maintained or while it was held at a fixed value.’
Mr. Rowe explains, ‘These pulses allowed for the digital transmission of data to and from the transmitter for both reading measurements and status as well as for configuration and calibration.’
Start of the dance
‘4-20 mA has been an industry standard for analog communication of process variable information for approximately 30 years. About 40 years ago when electronic signal transmission was in its infancy, 3-15 mA was proposed by some in the industry because of its familiarity as a standard range used for pneumatic signals,’ says Mr. Rowe.
‘A competing signal range of 10-50 mA was used for some time, but as electronic components advanced, the attractiveness of operating at lower voltages won out and 4-20 mA was adopted universally,’ adds Mr. Rowe.
Research was undertaken to learn more about present perceptions and attitudes of Control Engineering readers involved in specifying, recommending, and/or buying process variable transmitters. Out of 1,500 readers polled, 329 completed the survey for a 22% response rate. Here are some highlights from the survey:
Over 90% of respondents use temperature and pressure transmitters, while over 80% use level and flow transmitters.
37% of respondents say they prefer to specify/buy integrated units. Fifty-two percent have no preference between integrated units and individual components because it often depends on the application. And, 11% say they prefer individual (separate) components.
64% of respondents say raw materials processing industries best describes the industry segment for their company’s primary end product or service; 10% say their company’s end product or service is manufacturing of machinery and equipment; while 8% responded other fabricated metal and miscellaneous manufacturers were the end product or service.
94% of respondents now use 4-20 mA as their communication protocol for transmitters; 35% use HART; Ethernet comes in third with 20% use among respondents. (See graph.)
Although 4-20 mA appears to be ‘the belle of the ball,’ Louis DiNapoli, transmitters product manager, Siemens Moore (Spring House, Pa.), says, ‘Digital field buses such as Profibus, FOUNDATION fieldbus, and others allow digital communications over a pair of wires. This digital communication allows much more information to be sent, rather than just a single process variable.’
Mr. DiNapoli adds, ‘While these represent less than 10% of the transmitters installed today, it is a new concept in transmitter technology that will gain in popularity.’
Endress+Hauser’s Mr. Wesstrom agrees other protocols may come to the forefront, but not in the near future. ‘Profibus and FOUNDATION fieldbus are fully digital protocols battling it out. However, interest has cooled,’ in his opinion, ‘because it has taken too long to find a standard.’
Mr. Wesstrom says, ‘To go fully digital is expensive,’ although some would contend it’s less costly, factoring in installation and life-cycle costs. ‘Companies may go with digital for brand-new installations,’ he adds, ‘but a lot of revamping is going on instead of building new systems.’
Mark Menezes, manager of pressure and PlantWeb, Fisher-Rosemount (Chanhassen, Minn.), says, ‘The key new functions in PVTs are advanced process diagnostics, that is, the ability to diagnose the entire system from the transmitter, such as plugged impulse lines, eroded orifice plates, etc. Increasingly, we are finding that users ask us to ship preassembled, leak-tested, and integrated systems instead of ‘loose’ transmitters. This reduces their installed cost and risk of mis-assembly.’
Multiple dance partners
When asked what percentage of transmitters are multivariable (MVT), on average, 22% of respondents’ total transmitters are in this category. Mr. Wesstrom states that while MVTs are desired by end-users, the trend has not taken off as anticipated.
The future of MVTs seems bright, and, some say, the jury is still out on whether or not multivariable processes will dominate future industrial control.
Siemens’ Mr. DiNapoli foresees other uses for process variable transmitters. He says, ‘Smart microprocessor-based electronics allow the transmitter to become a source of diagnostic information for various conditions that occur in the process. This allows the user to better analyze process problems when they occur.’
Interconnectivity via networks, websites, mobile phones, and pagers will make information delivered from transmitters even more useful, throughout the enterprise and supply chain.
Process Variable Transmitter Products
For more information on process variable transmitters, circle the following numbers, or visit www.controleng.com/freeinfo. For a broader listing of PVT manufacturers, go to Control Engineering Buyer’s Guide at www.controleng.com/buyersguide.
Transmitter offers higher static pressure
Greenwood, Ind .-Deltabar S differential pressure transmitter now offers higher static pressure tolerance, along with pushbutton configuration without the pressure source. The transmitter comes with a standard Hastelloy C276 diaphragm and can be equipped with a totalizer for flow. Ideal for applications in chemical, water/wastewater, and power industries, the device provides reliable measurement of differential pressure, level, pressure, and flow.
MVD technology with modular architecture
Boulder, Colo .-Micro Motion Series 1000 and 2000 transmitters combine multivariable digital (MVD) technology with a modular architecture. Front-end digital processing is said to reduce signal noise and give faster response time, compared to analog devices. MVD technology allows the user to measure multiple variables; choose integral or remote mounting with a standard four-wire signal cable; choose transmitter capabilities based on the application; and upgrade transmitter functionality as needed. Series 1000 transmitters are best for applications that require single variable measurement. Series 2000 transmitters measure multiple variables simultaneously, and have more output and digital communication options.
Convert, isolate signal with single module
Harrisburg, Pa .-MCR-T/UI module can accept any RTD/thermocouple signal and convert, isolate, filter and amplify all in one Class I, Div. 2, approved module. RTDs in platinum, copper or nickel can be converted to a standard industrial analog signal. Module temperature range is -200 to 800 °C for RTDs, and -200 to 2,300 °C for thermocouples. Standard features include a programmable high/low transistor alarm output at 24 V dc and 100 mA switching capability.
Phoenix Contact Inc
Intrinsically safe, explosion proof
City of Industry, Calif .-FCX electronic transmitters are said to be intrinsically safe and explosion proof. From sealed sensing systems to high-powered RTUs, the FCX measures, displays, alarms, and provides level, pressure and/or flow data. Typical industrial and commercial installations include oil and gas, food and beverage, chemical, power, water, and wastewater. FCX can be purchased as traditional analog 4-20 mA with
Barton Instrument Systems
Transmitter and receiver all in one
Logan, Ut .-MF Series microwave flow controls feature fast response time, easy adjustment by virtue of an LED bargraph display, and easy installation. MF Series sensor contains the microwave transmitter and receiver. The microwave signal is transmitted by the converter and reflected by a solid particle. MF Microwave Doppler Flow is designed for flow or plugged detection of solids and powders in a nonmetallic pipe, tube or chute. Typical applications include pneumatic or gravity conveyance of food products, pharmaceuticals, building materials, Styrofoam beads, or sawdust.
Scientific Technologies Inc.
Measure vibration on plant machinery
San Diego, Calif .-HI 5701VT vibration transmitter is a two-wire, loop-powered transmitter used to measure vibration on plant machinery. It connects directly to a DCS, PLC, or other monitoring instrument, providing a low-cost method for monitoring running condition of pumps, fans, motors, or other machinery. HI 5701VT attaches to a bearing housing, or other critical measurement point on a machine.
High accuracy in various ranges
Michigan City, Ind .-Series 634S pressure transmitter uses an isolated piezoresistive sensor to provide pressure readings of air and non-corrosive gases or liquids with
Dwyer Instruments Inc.
Runs on batteries and solar power
Lenexa, Kan .-CSA certified for use in Class 1, Div. 1 explosion-proof and intrinsically safe applications, Series 536HS low-power pressure transmitters meet the needs of field automation personnel in the oil and gas industry, onshore and offshore. The low 536HS current consumption is said to be ideal for use in systems that rely on batteries and solar power. The accuracy (m0.25% of calibrated span) of its thin-film sensor combined with 5:1 turndown capability allows for measurement as low as 400 psi. Transmitters provide a 1-5 V dc output with current consumption less than 1.5 mA.
Panel mounting in various enclosures
Lakeland, Fla .-TW300 Series compact, two-wire transmitters are designed for mounting inside a thermocouple head or for field or panel mounting in various industrial enclosures. TW Series transmitters are resistant to harsh atmospheres and vibration found in industrial applications. Transmitters are set to customer specifications at the factory, but are field adjustable over
Wilkerson Instrument Inc.
Norristown, Pa .-Model 276C, a leak-proof, two-wire submersible pressure transducer, is ideal for measuring levels of corrosive chemicals, as well as water and wastewater. It is available in eight depth ranges from 5 to 65 ft of water, full scale. It has temperature compensation to ensure high accuracy over wide temperature ranges found in process plants, water, and wastewater treatment. And, it can operate with an unregulated power source (12-38 V dc).
Transicoil, a Div. of Horizon Aerospace