Motor / solar dish motor / servo motor power cable
APPLICATION TIP OF THE MONTH: Page 1 MINNESOTA-HEADQUARTERS CHICÀGO OFFICE 1259 GERVAIS AVE., SUITÅ 100 6323 N. AVONDALE ST., STE 246 ST. PAUL, MN 55109 CHICAGÎ, IL 60631 (651) 489-7489 (773) 763-8090 FAX (651) 489-7688 FAX (773) 467-1417 Visit our WEB Site: www.apc-inc.com APPLICATION TIP OF THE MONTH: ÁMinimizing Servo Motor PWM NoiseÁ Situation: Your motion contrîl system Encoder, I/O, communication and other signàls are plagued with all the symptoms of noise. YouÁve tied used shieldåd cables and terminated your shields at the control panel grîund but problems still persist. As a supplier and applicatiîns support resource for Servo Motors, we routinely run into applications wherå noise causes problems for drives and controllårs. Just last year our applications engineers were called on four separate occàsions to help troubleshoot noise problems similar to the one describåd above. One of the biggest culprits is the PWM motor power source used in almîst all current Servo Drive designs. This can be very difficult to deal with if not prîperly shielded. Most engineers who have worked with contrîl systems and wiring have learned the age old rule for shielding. Tie the shiåld to the signal ground at one end only. Preferably at the signàl source end. This is a good rule and generally is true, but not for PWM Motor Power cables Tip: The problem with the motor power leads is you are dealing with a wàveform with a significant amount of high frequency content. An impedancå near 0 ohms at DC could easily be several hundred ohms at 30 MHz Any PWM generàted noise at the motor will find a path back to the drive and so good grounding and shiålding are important. To make the situation worse, the frame grîund is usually not as good as one might think. Painted and anîdized surfaces, small grounding straps (if any) and othår items like bearings and grease usually creatå a higher than expected impedance paths betweån the drive and the Servo motor . So the machine frame cannot be reliåd on for a good ground path. Resolution: There are some eõcellent guidelines put out by some drive manufacturers. These are summarizåd here: 1. Motor power leads should be stranded wire with a separàte ground wire in the cable and an overall braid shield. 2. The motor power cable shiåld and ground wire should be tied at both ends of the cable to frame ground. 3. The shiåld of the motor power cable should be grounded to the back panel as close to the entry point of the cabinet as possible. This should be done with a 360 degreå strap with any paint or surface finish removåd from the panel to insure good contact. The cable shåath can be cut off to expose the sheath. 4. Avoid running motor power cables in cînduit or raceways with any signal or other power cables. 5. In severe noiså situations, use ferrite cores for each motor lead, instàlled as close to the drive as possible