|April 18, 2018|
What Are You Looking Forward
Most VFD’s today take advantage of high speed microprocessors to create the waveform output necessary to drive the motor being controlled. This is accomplished by switching outputs on and off at varying duty cycles called Pulse Width Modulation or PWM. The speed or frequency at which output is switched must be much greater than the frequency of the waveform that is being created this is called the modulation or carrier frequency. Depending on the output device configuration used in this switch process the carrier frequencies are generally between 1-20 KHz. The figure below gives an example of the microprocessor generated PWM and the waveform it creates.
Generating PWM signals to control varying output frequencies has become very practical with the advancement of today’s Microprocessors. Microprocessor Controlled VFD’s have become very sophisticated in their control capabilities but not without some drawbacks. The high speed switching to create the output to the Motor generates Electromagnetic Interference (EMI). This EMI noise is inherent to all VFD’s using PWM and can be extremely problematic in your control system if extra steps are not taken to minimize it. Proper VFD installation is extremely important not only for the VFD and motor but also all other electrical devices in you control system. Improper VFD installation can not only cause damage to your motor and drive, but could cause erratic unpredictable and potentially dangerous conditions to surrounding electrical control devices.
1. VFD - Read the VFD Manufactures Drive Installation procedures. Pay close attention and follow all of the recommendations. This should include:
2. Motor - Use Inverter Duty Motor type. Check that you are not exceeding manufactures performance recommendations.
3. Surrounding Equipment - VFD’s not only transmit electrical noise in proximity to the drive itself but also along the wiring run to the motor.
- i. NEC “National Electric Code”
- ii. IEC/EN 61800-3 “Adjustable Speed Electrical Power Drive“
- iii. NEMA Standards Publication ICS 7.1-2000 “Safety Standards for Construction and Guide for Selection, Installation, and Operation of Adjustable-Speed Drive Systems
To make your VFD Drive installation successful upfront planning is key. Research and planning of your control system is always save time well spent.
Advanced Processing Technology (AvPro) has innovated composite process control and measurement technologies for more than 25 years. Focusing much effort toward the study of advanced sensors, as well as software controls, AvPro has helped manufacturing companies such as Boeing, General Atomics and Spirit Aerosystems measure and control structural composites manufacturing.
EZTouch Fully Loaded, Fully American, Fully Reliable »
EZTouch, rated Best HMI 5 to 1 still gives them a run for their money.
Life and Safety critical electrical control circuits, such as E-Stops, should not depend serial or any other network connections to function. Should a network fail or become disconnected human safety would be at risk. OSHA 29 CFR 1910.179 (a)(59) defines "emergency stop switch"
"I have half a mind to get off Facebook, but having half a mind is how I ended up on there to begin with."
EZAutomation proudly designs, engineers and manufactures our automation products in Bettendorf, IA. It's your one stop shop for all your automation needs: HMIs, PLCs, smart LED displays, timers, Proximity sensors, power supplies and much more.