NHP Electrical Engineering Products Pty Ltd A.B.N. 84 004 304 812 www.nhp.com.au AUSTRALIA 100 percent Australian Owned VICTORIA MELBOURNE 43-67 River Street 5 6 Richmond VIC 3121 Phone (03) 9429 2999 are at the closest (see not all solutions can be shielding. It is definitely with the o Fax (03) 9429 1075 recommend- ideal angle is at 90 . NEW SOUTH WALES equation.C: (cos ø = found and explained. earthing that most ECHNICAL NEWS SYDNEY T cos90=0 ). However, most problems Filtering problems occur. There ations F) Optic fibre cables are 30-34 Day Street North, Issue 29 October 1999 can be solved by is a major difference increasingly attractive Silverwater NSW 2128 Phone (02) 9748 3444 observing the following between a safety earth alternatives to copper Please circulate to Shielding for The use of filters in A) The communications Fax (02) 9648 4353 guidelines. and a EMI earth, cables should be laid as conductors for data NEWCASTLE _________________________ suppressing EMI from communications circuits 575 Maitland Road inductive especially at higher far from the power Mayfield West NSW 2304 _________________________ The main problem of EMI VSDs is aimed at Quarterly Technical frequencies. What is cables as possible at the in high interference Phone (02) 4960 2220 _________________________ is interference to sensitive preventing the Fax (02) 4960 2203 Newsletter of Australia’s coupling needed for EMI is a low outer extremes of the environments. Fibre _________________________ equipment nearby. Noise interference passing QUEENSLAND leading supplier of EMC- What’s HF impedance earth cable ladder or duct. cables do not suffer from BRISBANE low-voltage motor _________________________ is coupled into the down the lines and also Surrounding the victim system. The standard (The cable ladder or duct coupled noise or 25 Turbo Drive control and switchgear. earthing system and on aimed at changing Coorparoo QLD 4151 conductor with a earthing presents a should be made from a longitudinal voltage all the Noise the cable from the drive to impedance conditions so Phone (07) 3891 6008 conductive shield that is relatively high conductive magnetic stresses. Fax (07) 3891 6139 the motor. Once in the earthed at both ends that EMI on the ground impedance at HF due to material, such as TOWNSVILLE earth system these Referenced material: 62 Leyland Street about further reduces the system is re-directed skin effect. This high galvanised steel). Garbutt QLD 4814 interference currents induced noise voltage. back to its source. On impedance results in Henry W. Ott, “Noise Phone (07) 4779 0700 By Craig Dunne This is because a voltage circulate to other greater levels of B) If possible, the power Fax (07) 4775 1457 the input side of the Reduction Techniques in ROCKHAMPTON equipment, then the cables laid up in trefoil is induced in both the VSD, the use of radiation from the Electronic Systems”, 14 Robison Street NHP Electrical Engineering higher frequency and preferably armoured Rockhampton QLD 4701 Definition of EMC: shield and the victim capacitors is effective in system (and increase John Wiley. Products Pty Ltd components will radiate to minimise the Phone (07) 4927 2277 conductor from the source suppressing the EMI. sensitivity to external Electromagnetic Fax (07) 4922 2947 interference to other associated EM fields. The ability of an electronic system to: conductor, but then the interference). Compatibility Lecture TOOWOOMBA Development Engineer systems causing further Cnr Carroll St & Struan Crt shield in turn induces a Together with a choke Notes - (A/Prof S 1 function properly in its intended problems. (see figure 5) significant benefits can C) The cable trays, Toowoomba QLD 4350 electromagnetic environment and voltage on the victim Shielding/ Shihab), “Earthing, Phone (07) 4634 4799 be seen when using such ducts, conduits and Fax (07) 4633 1796 conductor but with a The higher EMI Shielding, and Surge reversed polarity. The a filter. Input filters are barriers should be CAIRNS 2 not to be a source of pollution to frequencies must be Screening Protection of Electronic 14/128 Lyons Street used to prevent electrically bonded that environment. voltage on the victim prevented from radiating Equipment for Bungalow QLD 4870 conductor is then the harmonics from affecting together at every join. Phone (07) 4035 6888 by using screen cable, It is almost essential that Instrumentation and Fax (07) 4035 6999 Interference is the undesirable effect voltage induced from the upstream apparatus. On They should be earthed good earthing techniques the cables from the VSD at least at both ends and Control” - Automated SOUTH AUSTRALIA of noise. If a noise voltage causes the drive output, however, ADELAIDE source minus the voltage and bonding. At this to the motor be shielded. Control Systems improper operation of a circuit, it is induced from the shield. the use of capacitors is at any other convenient 36-38 Croydon Road point one must realise that This screen should be Training Division WA, Keswick SA 5035 interference. Noise cannot be severely restricted due to locations. there is far more to the connected to both the “Taian T-Verters Phone (08) 8297 9055 eliminated but reduced in magnitude their effect on drive Fax (08) 8371 0962 EMI mechanism than just motor earth and the drive D) The communications Detailed Training” by until it no longer causes interference. performance. Often the WESTERN AUSTRALIA IN THIS the drive itself. A system earth and be continuous cable should be a Lew Mallia NHP PERTH output side filter consists 38 Belmont Ave Vnoise=Vsource induced approach is the best from VSD to the motor. shielded twisted pair, Electrical Engineering ISSUE Noise sources can be grouped into of a low value choke. Rivervale WA 6103 three categories: -VVashieldriable induced solution. That is, consider with electrostatic shield Products Pty Ltd. Phone (08) 9277 1777 Fax (08) 9277 1700 the way that the drive is earthed at one end. ■ The positioning and Practical NORTHERN TERRITORY The widespread use of electronic circuits intrinsic noise, Speed Drives installed. installation of these E) Where data cables DARWIN for communication, computation, 3 Steele Street ■ noise due to natural disturbances devices are critical. automation, and other purposes makes it VSDs employ high To further reduce the cross power cables, the Winnellie NT 0820 such as lightning and effects of coupling, lets Phone (08) 8947 2666 necessary for diverse circuits to operate frequency switching of Fax (08) 8947 2049 ■ voltage and current take a closer look at Earthing TASMANIA in close proximity. All too often these man-made noise, such as motors, • Definition of EMC commonly known as filtering, earthing and HOBART 1 circuits affect each other adversely. switches, digital electronics and 2/65 Albert Road Nowadays more then ever circuit radio transmitters. Pulse Width Modulation Contact NHP for all your Moonah Tasmania 7009 (PWM) to obtain high Phone (03) 6228 9575 • Cabling 2 designers need to do more than just make efficiency and low Fax (03) 6228 9757 their systems operate under ideal NEW ZEALAND •Resistive and Capacitive conditions in a laboratory. Besides this Coupling Modes acoustic noise in the switchgear requirements NHP Electrical Engineering Products (NZ) Limited Coupling obvious task they need to ensure that motor, such frequencies 3 Three types of coupling are considered result in EMI and RFI at 7 Lockhart Place their equipment works with other Mt Wellington Auckland NZ equipment nearby without being affected in this article. the switching frequency from the one source Phone 64 9 276 1967 • Inductive Coupling 4 and harmonics of this Fax 64 9 276 1992 by external noise sources and should not ■ resistive (or conductive) coupling, 476 St Asaph Street itself be a source of noise to the frequency. As EMI and Linwood Christchurch NZ •Variable Speed Drives 5 RFI can involve very Phone 64 9 389 7604 environment. Electromagnetic ■ capacitive (or electric) coupling and complex coupling modes, Editorial content: - Please address all enquiries to 'The Editor - 'NHP Technical News' Fax 64 9 389 7605 Compatibility (EMC) should be a major Figure 5. Noise Coupled Into the Earthing System Version 6 ■ PO Box 199, Richmond Victoria 3121. • Practical design objective. inductive (or magnetic) coupling. Recommendations 6 NHP Technical News, issue 29 NHP Technical News, issue 29 TNL-29-8/99-14M 2 3 4 ...Coupling Modes (continued) Resistive We also know that the current capacitively coupled noise - ...Capacitive Coupling Inductive 3. distance from the through a capacitor has the provided that the screen is (continued) source (r) Resistive coupling is noise Coupling following relationship. connected to earth to provide coupling transmitted electrically a path for the capacitive the electrostatic screen is 4. area (A) and through a common ground usually earthed at one end To minimise resistive current. The coupled currents Inductive coupling occurs impedance path. A common dv only. 5. orientation of the area coupling, use filters either on then flow through the because two or more example is seen at home IC=C (eqn.B) (cosø) the source output or the dt capacitance C to the screen circuits are magnetically where television reception is However, when the screen victim's input or both in some and then to the earth, instead coupled through a mutual Knowing this, it's easy to impaired while a hair dryer is earthed at one end only, cases. of flowing through the signal inductance. After some conclude that cables operating in another part of In other words, the larger the the capacitively coupled conductors. complex derivations using carrying large currents are the house causes noise to be Isolation transformers will stray capacitance, the larger obvious noise sources and conducted through the house's Ideally with both the shield Figure 1. Inductive Coupling also reduce the effects of the current that will flow.