Control Engineering’s Process Instrumentation Enews — March 2002

By Dick Johnson May 30, 2002

In this issue:

  • Monitoring reciprocating machinery revisited
  • If you don’t touch it, you wouldn’t wear it out
  • An outpouring of data for the control engineer
  • A step in the right direction
  • Archive

Monitoring reciprocating machinery revisited

I remember it clearly-the reciprocating compressor experiment my colleagues and I did as part of an experiment in thermodynamics, ME 264 it was called then, at the old Mechanical Engineering Lab at the University of Illinois in Urbana. The four of us struggled with a mechanical indicator that actually traced PV diagrams when the compressor was cycled. The purpose of the experiment was to validate some then obscure (to us) thermodynamic compressor performance theory.

Thermodynamic theory has not changed. Cylinder pressure and position represent two very important measurements for reciprocating compressors. To that end, Bently Nevada Corp. , Minden, Nev., offers the 3500/77M Cylinder Pressure Monitor and the 3500/72M Rod Position Monitor. Examining the cylinder pressure profile is considered the best method of determining the overall health of a recip gas compressor. The pressure monitor uses permanently installed transducers located on each cylinder chamber. They collect pressure data along with crankshaft position to obtain continuous and performance data that provide information on the condition of the valves, piston rings, packing glands, and the crosshead pin. According to the company, recip-specific plot types such as dynamic PV curves can now be introduced in its System 1 software, allowing Bently Nevada to address complete condition monitoring needs for reciprocating machinery.

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If you don’t touch it, you wouldn’t wear it out

Well, not exactly, other things can go wrong. However, noncontact sensors have the advantage of reduced wear and tear and, hence, increased reliability because they remain out of harm’s way. According to the article ‘Contact Sensors Losing the Battle against Noncontact Sensors’ by Daniela Carrillo, research analyst for the Frost & Sullivan Sensors Group, noncontact technologies are making headway against traditional contact sensors is some industry sectors. Areas where noncontact sensors are said to be making inroads in process sensing applications include temperature sensing (thermocouple vs. infrared) and emissions monitoring and gas detection (catalytic vs. infrared).

For additional information on this subject, visit Frost & Sullivan .

For a February 2002 Control Engineering article on contact temperature sensing, click /archives/2002/ctl0202.01/020201.htm

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An outpouring of data for the control engineer

Wakefield, Mass. – WorldFlow Monitoring Service website includes four components: The Flow Barometer-a quarterly report on the flow industry, The Process Industry Monitor — a quarterly report on the process industries, User Perspective-a quarterly report on flowmeter users surveys, and an extensive database of flowmeter products arranged by technology.

For more information, visit WorldFlow Monitoring Service .

For recent Control Engineering flowmeter coverage, search our site, or visit /archives/2001/ctl1101.01/011101.htm and also see /archives/2001/ctl0801.01/0108pf.htm

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A step in the right direction

Rosslyn, Va. – Improperly disposed of mercury is extremely hazardous to the environment. With that in mind, Honeywell, General Electric, and White Rodgers established Thermostat Recycling Corp. (TRC) promote the collection of used mercury-switch thermostats for eventual removal and disposal of the mercury. Since January 1998 when it began operations, TRC has collected over 1,060 lb of mercury from nearly 123,000 used thermostats. TRC maintains operations in 22 states and the District of Columbia. According to Ric Erdheim, TRC’s executive director, there are no plans to expand the collection of the liquid mercury from other sensors or control components. The effort is run through participating controls wholesalers viewable on the web at .

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According to the results of a survey published in the March 1957 edition of Control Engineering , the top five non-electrical parameters measured by control engineers were shaft position, temperature, pressure, velocity, and flow. The survey further stated that the preferred mode of signal conversion for the top five, as well as the other nine (for a total of 14) variables mentioned, was voltage conversion. ‘Granted the universality of the shaft position parameter (so important in servo and analog systems), it is still interesting to see how the old `war horses’ of temperature, pressure, and flow dominate the measurements-a sure sign that so-called process variables prevail, no matter what the field or application.’ It is interesting to note that ‘level’ came in eleventh.

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