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  • Users: djs
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  1. djs

    A parent's question re: ChemE & CompSci

    My step son started college as chemistry major, but in his second year switched to philosophy. After that he got a masters and a doctorate in geology. No real push on my part. The switch to geology occurred in his junior or senior year when he was forced by the university to take a summer class...
  2. djs

    Government agencies limitation of scope

    In my area there was a reservoir built to hold water for the local municipalities during our dry season. The banks of the reservoir were initially designed to use rip rap to protect the banks. During the permitting process, the state DEP rejected the rip rap and specifies a soil cement covering...
  3. djs

    Interlocks and Pumps

    A year or so ago, I was involved with a jet fuel pipeline. This pipe line had two feed or priming pumps. Which pump was connected to the pipeline was determined by manual open close valves. What happened (once) during operation, the isolated pump turned on due to a control malfunction. No one...
  4. djs

    Fibre Optic systems "for dummies" (hopefully ok to ask) - coaxial testing

    Look at the fiber cables and the manufacturer's markings. The manufacturer, if still in business should be able to tell you if multi or single mode. Lacking that, see if the cable has one of the following markings: 62.5 um, 50 um, OM1, OM2, OM3, OM4. If so it is multimode. Single mode will be...
  5. djs

    FIBER OPTIC CABLE SIGNAL TRANSMISSION

    FO cables are high bandwidth - high cost. Usually used in digital signal transmission (Ethernet or something similar). In that case you would need a remote I/O at the signal source and a poller at the end which you want the signals to arrive. Usually two fibers are used, one for transmit and the...
  6. djs

    Speccing a Brake Resistor with missing information

    You could base the size of the resistor on the motor size. 40Hp is around 30KW. The VFD should prevent overloading the motor in deaccel, so 30KW would be the max wattage. You could probably go half that amount as the motor slows down the max power available also decreases.
  7. djs

    North Carolina power substations taken out by gunfire

    About 15 years ago, I installed an RTU at a dam on a water reservoir. This dam was located inside a large forested area. Took about 30 minutes driving on dirt roads to get to it. A couple weeks later, we received report that someone had shot at the RTU but did not penetrate the enclosure (316...
  8. djs

    short term spikes in the output

    I had a submersible level transmitter which would give wildly inaccurate readings when ever one of the pumps in the wetwell started. It turned out that the transmitter had an internal short to the exterior metal casing. Replace the transmitter and end of problem.
  9. djs

    Electric Power PE Exam Plan

    In most states, the route to a PE licene involves three steps: Take and pass the EI exam have at least 4 years work under a licensed PE Take and pass the PE exam. As you worked in what is called "industry exemption" the second step might be the hardest.
  10. djs

    Check Valves under no flow conditions

    What you need is a pressure limiting valve, not a check valve.
  11. djs

    Hi folks, I get two plc siemns s

    Fr communication to a computer, you can use any industrial Ethernet switch.
  12. djs

    Sanibel island causeway

    I just heard that the causeway is now open to utility trucks. Not yet open to the general public.
  13. djs

    Engine designs that have problems

    I had a European sports car that had a four cylinder engine with an overhead cam shaft. The cam shaft was driven with a timing belt and the camshaft also was connected to the power steering pump. Very funny feeling when you lose both drive power and power steering. Luckily that engineer was very...
  14. djs

    Sticky Situation: Advice Appreciated and Judgement Expected

    Just my opinion and experience. I work on the construction side of Municipal water and Wastewater facilities. It is my experience that the sealed contract documents are always "light" on details, and many are left for the contractor to fill in. This usually results in a very large number of...
  15. djs

    1MW motor startup cause Turbine Generator to (trip on Differential) why!!

    This maybe a stupid question, but if the trips occur after a long shutdown period, are your space heaters in the motor working? Could be moisture accumulating and causing ground currents.
  16. djs

    24 fiber optic cable.

    For very long runs, bandwidth can be an issue. With fiber there is a rating called Minimum effective modal bandwidth. It is the product of bandwidth by distance. The shorter the run, the higher the bandwidth can be used. For very long runs, the available bandwidth decreases considerably. One...
  17. djs

    Louisiana No power for 4-6wks

    These sort of events are wake up calls to the local utilities. In Florida, we had a hurricane come up the middle of the state. 75% of the state was without power. This prompted a boom for various tree surgeon companies. In many ways engineering is built on failures.
  18. djs

    using regular wire for a thermocouple connection

    I think a bigger question is how accurate is the temperature reading need to be? If +- 25 C is ok, then copper will probably be fine.
  19. djs

    Tap motor circuits without Dedicated Short Circuit Protection

    Check out the NEC tap rules, in this probably 240.21(B)(1). For a discussion please see this.
  20. djs

    Which is best Charting application software for drawing and displaying scientific and engineering ch

    Not cloud based but Excel works

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