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LVD 2014/35 Directiva de baja tensión de la UE

La UE lanza nuevas reglas para evitar la competencia desleal, a partir del 20 de abril de 2016 hay una nueva versión de la Directiva de bajo voltaje (LVD). Esta nueva ley afecta a los equipos eléctricos diseñados para uso con una clasificación de voltaje de entre 50 y 1000 V para corriente alterna y entre 75 y 1500 V para corriente continua, que no sea el determinado equipo especificado. Esta directiva está diseñada para mejorar la seguridad y prevenir la competencia desleal en el mercado, por lo que es probable que sea una buena noticia para nosotros que fabrica equipos en la UE y es malo para las empresas que importan productos baratos del lejano oriente. or favor, recoja a continuación para ver algunos de los puntos clave:

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Product marking: The important point is that there must be specific numbering must allow making a clear link to the relevant documentation that demonstrates the conformity of the specific type of product, in particular the declaration of conformity.

Manufacture and product information: Importance is given to the numbering system and making a clear link to the relevant documentation that demonstrates the conformity of the specific type of product, in particular the declaration of conformity.

Manufacture or importer marking: The manufacturer or importer must indicate their name, registered trademark and Name and address on the product. Article 6.6 (3) a single contact postal address on the product or, when not possible If lack of space, would be possible to indicate the name because of the size or physical characteristics of the product, on its and address within the product? packaging and/or on the accompanying documentation.

Safety instructions: Instructions and safety information need to be provided, whether the Instructions and safety information product is intended for consumers or other end-users. The Low Voltage Directive does not make a distinction on who is the user of the product. The documentation should include all the necessary information for the safe use of the product, to enable the user to assemble, install, operate, As Low Voltage Directive covers safety matters only, store, maintain, repair, and dispose of the product.

Importer: “Before placing electrical equipment on the market to keep it for 10 years after a product has been placed on the market. Article 8.2 importers shall ensure that the appropriate conformity assessment procedure has been carried out by the The importer does not have to have a copy of the technical documentation manufacturer. They shall ensure that the manufacturer has but has to ensure that the technical documentation can be made available to drawn up the technical documentation, that the electrical the competent national authority upon request. Equipment bears the CE marking and is accompanied by Even if there is no explicit obligation, the importer is advised to require the required documents, and that the manufacturer has formal assurance in writing from the manufacturer that the documents will complied with the requirements set out in Article 6(5) and be made available when requested by the surveillance authority. But the (6)” technical documentation can be given directly by the manufacturer to the surveillance authorities. What is important is that the authorities receive the How do we interpret “the market importers shall documentation and that at importer's request the manufacturer provides the ensure”? Does it mean that the importers must have a information to Member States. copy of the declaration of conformity and the Technical Documentation?

Instructions article 8.4: “Importers shall ensure that the electrical equipment is the instructions and safety information. Manufacturers, importers and accompanied by instructions and safety information in a distributors have the obligation to ensure that the product is accompanied language which can be easily understood by consumers by instructions in a language which can be easily understood by consumers and other end-users, as determined by the Member State and other end-users, as determined by the Member State concerned.”

Technical Data: “Directive 2014/35/EU Annex III.2 requires from the documentation start a risk analysis of the specific risks of the product to address them in manufacturer to include an appropriate risk analyses and order to comply with the essential requirements of the Directive because Annex III.2 evaluation in the technical documentation without providing any further details.”

All this means is that if you buy equipment it should have a risk assessment and that with this risk assessment you do not need to do your own risk assessment. This is good news for all companies that buy equipment

What does this mean to machine builders? Basically most things concerning machinery are covered in the machinery safety directive. But in some respects the directives overlap and so the best this is to make sure that where possible electrical items in reach of the operator are low voltage and pose no risk of shock etc.

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Do I need a Risk Assessment?

The short answer is yes: “If you are an employer or self-employed. It is a legal requirement for every employer and self-employed person to make an assessment of the health and safety risks arising out of their work. The purpose of the assessment is to identify what needs to be done to control health and safety risks.  Regulation 3 of the Management of Health and Safety at Work Regulations 1999.” (From the Health and Safety Executive Website - http://www.hse.gov.uk/risk/faq.htm#q8 ). Written by Businesswise Systems Ltd

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This means that you need to consider the safety of your employees and other persons not in your employment arising out of or in connection with your undertaking. Failing to carry out proper risk assessments could result in accidents occurring and injury to people or property. Such damage might constitute criminal offences. This is so even if no harm was caused. In February 2016 tougher sentencing guidelines were introduced, including Corporate Manslaughter and Food Safety & Hygiene Offences. In the most serious of cases this could result in your business being closed and custodial sentences if a Director of a company is found to be guilty of “consent, connivance or neglect.”

Accordingly, be prepared. Seek advice and properly assess risk and procedures to protect your business, staff and persons coming into contact with your business. Businesswise Systems will be pleased to provide a free 30-minute telephone consultation and review your health & Safety needs. Please call on 07805 658299.

What is a ground loop?

Motion controllers and automation systems use sensitive analogue signals. To protect these analogue signals from being influenced by other signals such as hum and whistle in the case of audio signals, an outer connection which is made out of foil or braided wire is often included around the cable or groups of conductors. This is commonly called a shield and its purpose is to provide a barrier reducing the amount of noise or other signals often called "crosstalk" that effect sensitive signals.However if current is allowed to flow in the screen it can actually make things worse therefore grounding a screen at both ends is not recommended this is called a ground loop

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Ground loops can be avoided by connecting the screen at only one end. It is good practice to try and have all the screens connected to the same point this is often called start point and it should be connected to earth. It is very important therefore to ensure that the screens are connected at one end. People often think that a big machine made out of metal will not have a voltage across it and therefore connecting the screen at both ends will have no effect. Unfortunately this is absolutely not true especially where high-frequency signals from motors et cetera are concerned. High frequencies can regard solid lumps of metal as a very high impedance and therefore considerable voltages can occur across a seemingly solid lump of metal.

A good way of testing is to use an oscilloscope. However connecting screens only one end normally will eliminate all ground loops. There is a black art to getting rid of noise in digital and analogue systems, it can be extremely difficult to get systems to work especially in noisy environments. It is therefore recommended that noisy signals such as motor commutation are kept as far away from sensitive signals as possible. It is a good idea to put screened cables in a metal trunking as this enhances the screening. Connecting the screen at both ends almost always causes problems as does multiple connections to the screen which must always be avoided.

Motor Current Torque and power

Engineers often get confused between motor ratings and the amount of power they need to provide. In most cases the answer is that the capacity of the power supply can be considerably lower than the stall current.

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In order to decide how much power is consumed by a machine during a movement, it is necessary to analyse what is going on and how much work is actually being done. Most machine manufacturers try to use the smallest and therefore lowest cost motor is possible, this is obviously common sense it also saves energy. Larger motors have much larger masses and therefore inherently use more energy during acceleration and deceleration.

However the vast majority of processes use very little actual power. For example if the stall current on a particular motor is 10 A and the motor runs at a hundred volts many people will simply multiply the voltage by the current and calculate 1000 W. This might well exceed the rating of the motor. In the vast majority of motion control applications the majority of current usage occurs during acceleration in which case often the current exceeds the motors maximum. However during this maximum current the voltage across the motor will be low and therefore the current is high and voltage low equals low power. In very few applications does the motor operate at high torque throughout the entire cycle. Inside the drive there are capacitors, these capacitors store energy and when the motor demands high current, energy is taken from the capacitors which can supply considerable current spikes. In effect they can be thought of as converting voltage to current. Therefore a motor that can be drawing 10 A might only draw one from the supply.

However where the motor is on continuous load in applications such as extrusion it is important to remember that the motor will be running at high speed and high torque. In order to run at high speed this will require a high-voltage, and a high torque requires a high current therefore the power consumption will be high. In this type of application the power supply should be rated higher than the maximum rating of the motor. However if we imagine the normal motion control application the loads can be very low therefore the voltage across the motor may be high but the current will probably be low. In this type of application when the current is high the voltage will be low and vice versa. In this type of application it is possible to calculate the current draw and calculate your power supply accordingly but often the power supply can be rated at 50% or so of the motor rating this saves an enormous amount of money..

What is a quadrature encoder?

There are a minimum of two outputs from an incremental encoder that form the distance measuring part of the output signal. These are the A and B signals. These two signals are 90 degrees out of phase with each other. The encoder therefore sends out two signals each of which has a rising and a falling edge, counting each edge therefore gives 4 electrical pulses to each mechanical pulse. which is what quadrature means, most rotary encoders are rate in pulses per rev (PPR) and the output gained from this is the PPR x 4, for example a 1000 PPR encoder gives 4000 electrical pulses. These signals are decoded to produce a count up pulse or a count down pulse.

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When the encoder is turned in one direction the A pulse leads the B and when the encoder is reversed the B pulse leads the A. The decoding device in the controller uses this fact to properly encode the distance measured by rotating the encoder. To make the signal more robust most encoders have tow more signals these are the Not A (A\)and Not B (B\) signals, there is nothing special about these signals they are simply the A and B signals inverted. The receiving device uses the polarity of both the A and A\ to determine the real status of the A signal as it does for the B signal. If noise is present in the A signal is is likely that the A\ will suffer the same disturbance and so the noise signal will have no effect overall.

Some encoders also have a signal that is only active for one pulse per revolution this is known as the Z pulse, the reason that this pulse is provided is that the exact rotational relationship is know relative to the mechanical position of the encoder. Normally on initialisation the Z pulse can be used so that when the axis moves off a switch away from home the Z pulse is used to reset or set the encoder counter to a known point normally zero.

What is a following error?

Following errors are what causes motion on motion control systems they are normal

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When a motion controller needs to cause motion in conventional motors, it does so by producing a voltage which is equal to the current or the velocity demand that the controller has calculated is need to make the motor move. Depending on the way that the drive is set up, that voltage applied by the controller is equivalent to the current (current mode) that the drive will endeavor to apply to the motor or to the velocity desired (velocity mode).

This signal is proportional principally to the position error multiplied by the gain, it therefore follows that to cause motion there must be a following error. A following error is a normal for a servo motor that is moving. A motion controller operates on a regular time period often called a “sample period”, the position errors will accumulate and this causes a high demand voltage to be output. Depending upon the response time of the servo motor and drive this following error can easily equal the accumulated error from several sample periods. It is not uncommon for this error to be that of 5 or more sample periods. This is worth while considering when setting a following error limit in your motion controller, setting this too low may result in false tripping, set it too high and it may have a limited effect.

What is DC Servo Drive?

A DC servo drive is a device that controls a DC servo motor or a DC motor

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When a motion controller needs to cause motion in conventional motors, it does so by producing a voltage which is equal to the current or the velocity demand that the controller has calculated is need to make the motor move. Depending on the way that the drive is set up, that voltage applied by the controller is equivalent to the current (current mode) that the drive will endeavor to apply to the motor or to the velocity desired (velocity mode).

The DC servo drive is normally a device that controls the current to the motor. There are two main types these are four quadrant or two quadrants. Four quadrants are famed for being more stable but are a lot less efficient. Quite simply when there is a motor command signal the drive uses the inductive nature of the motor to drive a pulsed width signal to the motor to control the current in the motor. All drives have a current control circuit and some also have a velocity control circuit. Where the drive aims to control velocity it must have some form of feedback normally these are Tacho generator or encoder. In the velocity mode the current applied to the motor depends upon the velocity where when the velocity is low the current will be high and vice versa. In systems with a motion controller current mode, where the current is proportional to the control voltage is the preferred option.

How do I install a motion controller for CNC welding applications

Most welding applications are quite easy to setup and run, the PMC4 is an ideal motion controller for welding applications. Working with Plasma cutter or TIG welders is more challenging because of the startup conditions.

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The startup phase of a Plasma cutter or TIG welder involves a high frequency signal and also a high voltage. In reality this is like a small transmitter, many welders also change the frequency cyclically, so they are likely to find a susceptibility in any wiring. Because of this susceptibility there is a need to shield all the cables and to make sure that even the motor encoders are shielded if not the encoders may become influenced by the startup signal. A very important thing is to ensure that electronic devices are shielded behind metal enclosures that are well grounded to a star ground. Only use shielded cables and make sure that they grounded at one end and connected to the star ground. it is also a good idea to shield the welding cables, but this must be done with great care as the shielding may effect the startup circuits of the welder. Maybe consider the use of flexible shielded trunking for the welder.

Automation enhances quality and reduces costs

Automation has many benefits including enhanced safety, consistent quality, reduced manufacturing cost and ease of manufacture. Some companies however find the technical side can be daunting, we are here to help your automation plans come to fruition. The Automation Manufactures Alliance is a group of UK manufacturers working together to assist companies with general automation right through to complex machine and motion control. This site is designed is designed to assist the reader to find the services they need on the relevant manufacturers websites. We are here to help we will try to get back to you within 3 working days, please use our services we want to help you

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