P Daniil

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About P Daniil

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  • Country Greece
  1. Driving a motor 250m away

    The motor construction and insulation should also be for use with an inverter . Non-inverter grade motor insulation and bearings will wear out quickly because of the long cable effects. Also, using a lower inverter switching frequency will not do much as it is the PWM waveform rise- and fall- time which cause the problem. Using a ruggedized drive (as BobLfoot suggests above) will also save you potential protective earth problems such as cable leakage causing fault trips and similar troublesome return currents.
  2. corection of position for servo motor

    The position drift you describe is typically caused by: 1. Loose mechanical coupling, backlash etc, and 2. Encoder dither. Our white paper looks at the problem and may be of interest.
  3. Sensing Foam?

    A capacitive level sensor should do it. What kind/chemistry of "soapy" foam is it?
  4. Reliance Flexpak Plus (DC Drive)

    In addition to the excellent posts above, a DC motor driven by a four-quadrant SCR drive still has an advantage when braking: All the generated braking energy flows back to the supply line during normal SCR commutation offering practically limitless braking capacity (effectively driving the grid´s infinite inertia) as well as superior power efficiency (no energy having to be dissipated in a resistor as in the case with AC drives). So if the application involves significant braking energies, DC drives have still one thing going for them.
  5. Encoder trouble

    There are many ways false counting can arise. With the encoder still, noise can arise from: 1. Wiring ground loops (as kaiser_will above correctly pointed), 2. Common mode noise entering through the encoder power supply, 3. Faulty encoder output electronics, 4. Absent/wrong termination at the input card (with differential signalling), and 5. Faulty/latched-up input card. With the encoder moving, in addition to the above the most common cause is so-called dithering or a worn/damaged encoder optical disc. You may find our paper (pdf, 238K) of interest as it discusses these problems.
  6. Preventing SSR chatter

    Most likely an external (SSRs rarely have them inside) RC snubber is needed to allow the SSR thyristor/triac to turn off graciously. The snubber RC values must be so calculated to limit the rate of voltage rising (dv/dt) at SSR turn-off for the given load (ie the relay coil) inductive current. SSR manufacturers usually provide typical values for typical loads and some of them offer ready, off-the-shelf snubber networks. Also keep in mind that an oversized snubber circuit will leak unnecessary current to the load which may prevent the relay/contactor to open.
  7. 1.2k to 6k rheostat wanted, links?

    Can't you use a small Voltage/Current Interface? (Potentiometer dividing the 24 VDC source to drive the interface to drive your 4-20 mA input). In this way you do not have to worry about linearity or potentiometer values.
  8. Converting a USA machine to France power

    Assuming this is an AC induction motor, as long as the V/f (volts to frequency) ratio is the same, you are OK. So as 480 x 50 / 60 equals 400 there is nothing to worry about the line supply. The motor however may not be able to develop the same power (ie increase the current to develop the extra torque needed) as this depends on the motor construction, power, slip and the load. The motors we get on this part of the world usually carry rating plates with 50 and 60 Hz sets of values. Is there a rating plate still on this old machine? If so, it may be of help. As a final check and to be on the safe side, I would drive the motor with an inverter at 400V/50Hz and see how the whole setup behaves. What is the power of the motor?
  9. Switched mode power supply

    My approach would be first to have two universal, galvanically isolated, wired-OR connected signals, "Fault" and "Ready", driving all the devices (PLCs, supplies, I/O etc) so that when any supply/device has a problem (load fault or source problem) it will signal the others to shut-down/wait graciously (as opposed to chattering to death). This arrangement has the advantage of enhanced robustness as you have one signal that there is an operational fault and a signal that all is working OK and being able to handle the four combinations accordingly. In more complex set-ups (such as in a ship) where you have separate power and control supplies it may also be worth having respective "Ready" signals for each line. Following this you can then look for suitable surge/UV/OV devices/controls.
  10. Fedora Linux

    I have not seen or heard of a bad Linux distribution. We started switching to Mandriva on all our PCs a few years ago and have never looked back since then. We chose Mandriva then because we thought that our learning curve would be flatter with this distribution at the time. (In retrospect all effort went to learning the Linux fundamentals and way of thinking and not so much on the particulars of the distribution). Most of the machines are set-up as dual-boot to run existing Win32 applications (mainly CAD and accounting) which we have not yet managed to run under the Linux WINE environment. Blue screens are now distant memories to be told to grandchildren like black and white TV.
  11. Switched mode power supply

    Edit: Good luck, please keep us posted.
  12. Switched mode power supply

    Most probably they got partially damaged during the "power problems" and as a result could not supply their loads with the necessary current (and hence the 5-10 Hz power-up "hiccup"). Most chances are that their dc-bus electrolytics got "savaged" from the line fault (typically high voltage 300-400 V inductive spikes riding on the 230 VAC line) as they are the most vulnerable part in a power supply. With a partially working electrolytic the power supply can only store and convert minimum/unloaded power. My further guess is that the line neutral became unstable during the coupling/uncoupling of the shore power and, just as it is always good practice, I would regardless power the PLCs through a 400/230V transformer and stay away from the neutral. Most faults involve the neutral and in a ship the presense of the hull (also at neutral) makes matters worse by offering a catch-all connection to the line.
  13. Encoder Connections to VFD

    There is no black or white rule here as it all depends on the particular encoder construction (isolated body, earthed common etc) and the frequency of the signals you are trying to protect. With RF (radio frequency, above 1 MHz) signals "plane grounding" techniques must be used as connection inductance (to ground) comes to play. In effect you ground the shield at as many points as possible to ensure a minimum inductance connection to reference (the "ground"). At lower frequencies, wiring inductance is manageable and "single point grounding" techniques must be used. By grounding at a single point you ensure that no current flows through the cable/body shield (and in effect turning it to a noise generating/receiving antenna) and that no noise-generating "ground loops" are formed. Grounding should ideally be done at the receiver or weakest signal end to ensure minimum noise at the input processing stages. In industrial electronics most situations do not involve RF signals and single point grounding is preferably used as it does not interfere/mix with any protective/safety earth (unless intented). So the way to go is to take into consideration the manufacturer instructions (the encoder construction), the signal frequencies involved and the overall wiring/cabling layout to judge how noise is generated and conducted/transmitted. I would start with the manufacturer recommendation if their example/model is the same as the installation at hand (in theory they have checked it and works OK) or with "single point grounding" and make the final decision in the field. Regardless, a tidy and clean installation with good ohmic connections is a must before looking at any noise problems.
  14. BooTP Helper Device

    As it saves IP related hassles, I would call it something like "Beyond IPs" or the more tongue-in-cheek "Forget IPs".
  15. programmable or specific controller?

    It depends on the physical shape and layout of the capacitor system. For such a system I would suggest an insulated rod type hanging immersed in the monitored fluid. We have succesfully used such sensors in potable water as well as ship grey water tanks. Capacitive sensors are less sensitive/suited for oil detection due to the lower dielectric constant of oil.