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  • Users: cokeguy
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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

    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...
  3. 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.
  4. 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...
  5. 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...
  6. 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...
  7. cokeguy

    VFD with small synchronous AC motor

    I need to run a small 120VAC/60Hz/72rpm single phase synchronous motor at one third or one quarter of its nominal speed. The obvious solution that comes to my mind is using a 220 VAC VFD (one of its output phases and neutral) to run the motor, and adjust output voltage and frequency...
  8. cokeguy

    Local area pagers

    Has anybody implemented or has references about a system for paging maintenance personnel within a plant? We want to implement one where our mechanics or electricians can carry a pager at all times and our alarm system automatically pages them when their intervention is required. Any ideas...
  9. cokeguy

    temperature effects on brushless AC servomotors

    Does temperature degrade the performance of brushless servomotors? I was told by someone at a motor repair shop that the permanent magnet of a servomotor can lose its strength if operated continously at high temps. I didn´t pay much attention to those remarks, but some of our motors are always...
  10. cokeguy

    Servo-motor maintenance procedures

    Are there any standard preventive maintenance or monitoring procedures for brushless AC servos? We use them increasingly more in our plant, but our verification and PM routines are designed for standard AC motors running at relatively constant speeds (vibration monitoring, lubrication...
  11. cokeguy

    RSlinx driver stopping

    We have recurrent problems with RSlinx and controlnet, specifically with the driver configured for the 1784-PCIC controlnet card, it stops for no apparent reason and we need to restart it frequently on the RSlinx "configure drivers" window because the status appears as "stopped". We use RSlinx...
  12. cokeguy

    synchronous motors running at low speed

    We use small synchronous motors (rated 345 VAC, 90 Hz, and with several sizes from 3 to 15 amps aprox) on some of our older machines, running from the same VFD to keep several mechanisms and conveyors in sync (newer machines have servos). We run the VFDs in V/Hz mode, with a 3.833 V/Hz ratio...
  13. cokeguy

    Fan types for wet scrubbers

    (I originally posted this on the HVAC forum, but I believe this is a more appropriate forum, since it is a scrubber-specific problem). Up to now, we have used radial type centrifugal fans in our scrubbers (blades extend from the hub straight out). We want to evaluate the use of backward-curved...
  14. cokeguy

    backward-curved v.s. radial in scrubbers

    Up to now, we have used radial type centrifugal fans in our scrubbers (blades extend from the hub straight out). We want to evaluate the use of backward-curved blades for our scrubber ID fans, could somebody point me some literature on the subject? I understand that radial fans are less prone...
  15. cokeguy

    Repairing vacuum pump?

    We have a damaged SIHI liquid ring vacuum pump, model LPH 60520, cast iron casing and ductile iron impeller. Inner surfaces are pretty worn out, with irregular "craters" throughout side covers and casing, some more than 5 mm deep. What amazes me is that the pump worked OK, up until the day...
  16. cokeguy

    V belt problem

    We have 4700 rpm fan (with 4.5 inch sheave) driven by a 3500 20 HP rpm motor (6" sheave), using 3 3VX-800 belts. Without bothering anyone with actual calculations, does this combination seem reasonable, should it work OK, even at those speeds? According to belt selection tables and guides...
  17. cokeguy

    S7-300 backup

    We wish to backup an S7-300 PLC, but we have no experience with Simatic controllers (99% of our equipment is A-B, we have all the software for them, but none from Siemens). Is there some sort of simple utility that lets you download/upload programs from an S7-300, or do we need to buy the whole...
  18. cokeguy

    Pulse train from a VFD

    We need to obtain a pulse per Hz signal from an A-B Powerflex 70 VFD in order to use it as a master synch pulse signal for a certain production line. The rest of the line is servomotor driven and is follower to this master pulse, no problem there. Right now we are getting this master synch...
  19. cokeguy

    STP vs UTP for industrial 100 Mbps ethernet

    We recently installed a machine whose user console is a PC hooked to the control cabinet through a 50 meter long shielded twisted pair ethernet cable, cat 5. It simply didn´t work, we even tried changing cable trajectories a few times but with no success. We then replaced the original vendor...
  20. cokeguy

    Bundling excess servomotor cable

    Which is the correct way to bundle excess servomotor power cable? We are installing a machine with 35 small (less than 1KW) servomotors, each one has about 10 or 20 meters excess cable, and we prefer not to cut it. I know that we shouldn´t coil it, so, for example, a possible solution would be...

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