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  • Users: abfer
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  1. abfer

    Communication with Point of sale terminal (POS)

    I don't know how pos terminals work. But i need to use a pos terminal in a project. Basically the microcontroller based system will tell the pos terminal the amount to charge the credit card of the customer and the the pos terminal will return the information of payment received or not. Is this...
  2. abfer

    Eliminating vibration effects from the output signal of a loadcell?

    As you know loadcells generally work in an environment with lots of mechanical vibration. So the output signal of the loadcell also vibrates very much. Averaging the output slows the output very much. Can we eliminate / filter out this vibration from the output signal wihout a much loss of the...
  3. abfer

    Loadcell Zero point shift

    What may be the reasons of the shift of readings in a weigh scale application? Evaluate the question from the developer's perspective also not only from the user's. Assume that there is no load on the loadcell and as time passes your readings change slightly. What are the reasons?One thing is...
  4. abfer

    What is admittance RF level transmitter?

    Are there any detailed information about it? I roughly know what it is from the product datasheets but i'd like to know it in more depth especially the theory behind it and may be some practical knowledge. Thanks.
  5. abfer

    capacitive level sensor measuring problem

    We are using a single probe capacitive sensor to measure the level of a grain. The grain is filled in a box which is installed on a machine. When the machine is running for a while we make the calibrations and there is no problem. But when the machine stops for a while and then restarts the...
  6. abfer

    Pressure to weight

    There are some weighing systems in some machines operated by hydraulic pistons and are quite precise. They calculate the weight by converting the measured pressure from the pistons via pressure sensors. Does anybody know or have an idea how the system works? How do they convert pressure to weight?
  7. abfer

    Motor Vibration Problem

    I'm driving a 2.2 kW induction motor with a 7.5 kW drive. In v/f mode, there's no problem but in sensorless speed vector mode, motor vibrates especially at lower speeds. Drive has a auto tuning function for parameter estimation but it does not work for rotor time constant without encoder. Anyway...
  8. abfer

    Lower current at higher speed?

    In a vector controlled drive with speed regulation mode, is it possible that drive draws lower current in high speed than in low speed at steady state and with same load conditions?
  9. abfer

    V/f profile and current drawing

    1- How does the current change with a 3ph induction motor which is drived in v/f principle and unloaded? 2- I'm trying to determine a v/f profile for a delta connected motor. But i couldn't be able to find a good profile. Due to dead time it's not good at very low frequencies. As frequency goes...
  10. abfer

    equivalent circuit at low frequency

    Can we expect ind. motor's equivalent circuit @1hz or so to behave like at higher frequencies or at rated frequency? If not what effects may occur?
  11. abfer

    rotor time constant or magnetizing inductance identification

    I need to find an induction motor's rotor time constant or magnetizing inductance (Lm) via inverter and while motor is at standstill. One way which i know is using bemf. But this method requires transient voltage measurement and the filter attached to the sensor doesn't allow to measure this...
  12. abfer

    carrier frequency and output frequency

    What must be the relationship with the carrier signal and modulator(output) signal. I mean at least what must be the ratio between them? Can i get a 1KHz spwm signal with 7KHz carrier signal?
  13. abfer

    Determining v/f profile

    I'm trying to drive a motor via a self made inverter. It's a small motor 360W, 230V, delta connected. I measured stator phase resistance as 135 ohm. It has no name plate on it but it's rated phase current is somewhat between 0.7-0.9A rms i think. The book which i look says, about determining the...
  14. abfer

    Motor parameter detecting

    When we measure resistance from the terminals of a motor with an ohm-meter, is it stator resistance (no matter about star or delta connection)? If so, is it also valid for leakage inductance of the stator (or rotor-stator combination since the measurement device will produce alternating signal...
  15. abfer

    Siemens motor parameters

    How can i obtain parameters of a siemens ac indcution motor like stator/rotor resistance, leakage inductances etc? Are there any source which contains that kind of information about siemens motors?
  16. abfer

    Inverter acoustic noise

    The 3 phase inverter is operating at 7KHz. When it starts, it begins to produce acoustic noise even no load is connected. It's coming from rectifier or inverter section i think; i couldn't exactly detect the source of the noise. Is this usual? What may cause this and how can i eliminate it...
  17. abfer

    How to and where to use twisted pair?

    I think twisted pair cables are used where differential signals exist. In a motor drive application where can we use this cable? Can we use it between the drive and motor powering terminals? How should it be? Twisting 3 phase cables together? I have a character based lcd near the inverter and...
  18. abfer

    Optical encoder selection for a motor control project.

    I have a motor control project. In this project, i need to measure the speed. To measure the speed, i planned to use a 100ppr incremental encoder. With the ucontroller's ability it can count 400 pulses per revolution.(It counts decreasing and increasing edges of phase A and phase B) This means...
  19. abfer

    Suppressing switching noise (spikes)

    I have some problems with switching noise at hard switching devices. I see the effects of this, for example, at the output of a dc/dc converter, or when i try to measure ac motor current etc. There are spikes on the signals that i measure, at the switching frequency. How can i eliminite these...
  20. abfer

    Connection to make motor stall

    What happens if i make a connection like this? U-V-W output of the VFD. X-Y-Z are terminals of a star connected induction machine. Connection: U------X V------Y |--Z W I mean W is free. X and Y terminals are both connected to V. X is connected to U. I think, V leg of the inverter is...

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