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  1. cokeguy

    monitoring servomotor current

    We need to monitor the current profile of several AC servomotors, in order to detect mechanical issues in the driven machinery. The drives we use have no connectivity options, so that is not an option. Should be no big deal anyway, except for the response time of the AC current transducer that...
  2. cokeguy

    Fan outlet pressure vs temperature

    It is an FC centrifugal fan.
  3. cokeguy

    Fan outlet pressure vs temperature

    Follow-up: I made a test today on one of the fans, at fixed speed (56 Hz), checking the plenum pressure under various conditions: The whole machine (10 molds) running: 58"H2O machine stopped (0 molds): 54"H2O 1 mold running: 56"H2O 2 molds running: 58"H2O 3 molds running: 59"H2O 4 or more...
  4. cokeguy

    Fan outlet pressure vs temperature

    thanks again for your comments. In the glass container manufacturing industry, maintaining stable mold cooling regardless of the day/night temperature swings has always been an issue, but the truth is that I´ve never seen a serious study or modelling of the effect of temperature swings on the...
  5. cokeguy

    Fan outlet pressure vs temperature

    Yep, if all or most of the dampers are open, pressure and temperature behave as expected. If none or only one damper is open, pressure begins to drop and temperature rises sharply.
  6. cokeguy

    Fan outlet pressure vs temperature

    It has always been that way, on every machine, in fact this setup up is standard in all glass bottle manufacturing plants, but only on that machine have we noticed that behaviour of "surging" (or whatever it is) causing that pressure decrease/temperature increase when airflow decreases.
  7. cokeguy

    Fan outlet pressure vs temperature

    In a glas bottle machine, airflow is directed from the fan's outlet plenum into pass-through openings in the cast iron bottle molds. The machine can have up to 10 molds working at the same time, and each mold has its own automatic damper that opens only when the corresponding mold is actually...
  8. cokeguy

    Fan outlet pressure vs temperature

    I understand your point Drazen, we use fan speed to control outlet pressure (we don't have outlet flow measurement) and thus airflow, which makes the actual cooling job. But we were wondering if perhaps there was a point where the temperature increase due to the increased pressure would...
  9. cokeguy

    Fan outlet pressure vs temperature

    Our glass container manufacturing plant has several 350HP VFD-controlled fans for bottle cooling. They normally run close to full speed (60Hz), since the outlet pressure setpoint is normally set to 60"H2O, the fan´s rated pressure at rated airflow. However, since we would like to have the...
  10. cokeguy

    filling the gap between thermowell and RTD?

    What can I use to fill the 1/4" gap between the tip of an RTD and its thermowell? something that can be readily available anywhere, like grease, etc..? it is installed on an air duct, temperatures are low, 60 degC max. thanks for your advise.
  11. cokeguy

    thermal massflowmeters for compressed air

    Actually the meter is downstream of 2 aftercoolers and a drier, however the air is almost always saturated when we measure relative humidity, since we have a less than optimal installed capacity of driers for our compressors. The issue here is to find out if thermal type flowmeters are adequate...
  12. cokeguy

    thermal massflowmeters for compressed air

    We aquired thermal mass flowmeters to measure compressor outlet flows (in the 70 psig, 8000-10,000 SCFM range), but we get very erratic readings from the instruments. I suspect it has something to do with moisture content (sometimes air is completely saturated), but the manufacturer mentions...
  13. cokeguy

    running a servomotor with VFD

    We still use a lot of synchronous motors in our plant, driven by VFDs in V/Hz mode, with sizes ranging from 3 to 10 HP approximately. Sometimes a single VFD runs 2 or 3 motors, so the VFDs are usually oversized to allow starting individual motors at normal speed without overcurrent trips. Since...
  14. cokeguy

    motor overheating with VFD, and incorrect amp readings

    Thanks for your comment. I really can't get rid of the VFD, because we do need to modulate fan speed in certain situations. We will install an inverter duty motor to diminish the probability of premature motor failure, but I will still try to find out why these guy heats up much more than its...
  15. cokeguy

    motor overheating with VFD, and incorrect amp readings

    Thanks for your comments. Frame temperature is measured either with thermal imaging camera or raytek type infrared thermometers, and temperature normally hovers somewhere around above 95 degC, much hotter than all the rest of the similar sized motors, either with VFD or DOL driven, which...
  16. cokeguy

    motor overheating with VFD, and incorrect amp readings

    We have a 350 HP fan driven by a VFD, the drive (saftronics GP10) has input 3% line reactor and DC choke, no reactor at the output. The motor always runs overheated, even though it has been running at 60 Hz for the past year or so. We want to try placing a reactor at the drive's output rather...
  17. cokeguy

    VFD with small synchronous AC motor

    Yes waross, it is similar to glass level control applications, I do need to slow down the motor close to the detection point in order to minimize overshoot. I plan to approach at normal speed, and close to the target begin a "slow speed by PWM" stage, and then back at normal speed. I'll tell...
  18. cokeguy

    VFD with small synchronous AC motor

    Excellent, thanks a lot Mobius, just what I wanted to hear!!!! I´ll test it right away. And thanks everyone else for your help.
  19. cokeguy

    VFD with small synchronous AC motor

    Guys, one final question on this matter (I hope): since the VFD option doesn't look promising right now, I'll try the pulse train using a solid state relay switched maybe 10 times per second or so. Do you think the motor will suffer too much and fail quickly if worked this way? Assuming I get...
  20. cokeguy

    VFD with small synchronous AC motor

    Update: I've been testing offline but cannot go less than 30 Hz without losing too much torque, and 30 Hz is not enough speed reduction for a process test. I paralleled another capacitor and boosted voltage, with no improvement. So now I guess my only choice for non-intrusive testing is...

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