Mitsubishi HD-5000A Specifikace stáhnout pdf (Strana 114)

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Please read carefully before choosing CE option.

The CE (Conformite European) mark indicates that a product complies with the European Union (EU) directives, and will affect you only if

your system is to be sold in Europe. CE does not describe the quality of a product, only that it complies with relevant EU directives and can be

incorporated into systems sold in the European market.

Select encoder Series manufactured by Encoder Products Company (EPC) are tested in accordance with harmonized standards to meet specific

noise immunity and emission requirements for an industrial environment, so as to comply with European directives. These tests ensure that,

when you order CE certified encoders from Encoder Products Company, they will operate without disturbing other equipment and without being

disturbed themselves. Testing for CE certification is performed on encoders with 6 feet of cable or standard body mount connectors. These

testing limitations should be taken into consideration any time the CE mark is ordered in combination with non-standard connectors or cable

lengths in excess of 6 feet.

It should be understood that CE wiring techniques may cause severe ground loops if used with systems other than CE certified systems. Therefore,

we strongly suggest that the CE encoder option only be used with CE wired systems, or in situations where the user has a clear understanding

of the CE requirements. For markets other than the EU, Encoder Products Company maintains the strictest tests to ensure that non-CE units are

shielded and grounded against electromagnetic phenomenon.

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When the electrical signals are generated by an EPC Accu-Coder™

encoder, they are electrically “clean” in the sense of being noise free.

However, due to a number of factors, these signals can be degraded

by the time they reach their intended destination Environmental

factors, such as radiated and induced electrical noise, can introduce

signal distortions. In addition, system design factors, such as cable

capacitance (especially over long cable runs), impedance mismatches,

poor cable quality, inadequate shielding, poor grounding, and poor

cable termination can all contribute to signal loss and distortion.

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All cables have small amounts of capacitance between adjacent

conductors. The amount of capacitance present is a direct function

of the cable’s length. As capacitance increases, it tends to round off

the leading edge of the square wave signal, decreasing rise times. It

can also distort the signal to the extent that errors are caused in the

system. Signal distortion is not usually significant for lengths less

than 30 ft (or 1000 picofarads). To minimize the distortion, a low

capacitance cable (less than 35 picofarads per foot) is recommended.

Cable lengths should also be as short as possible.

If it is necessary for the cable length to exceed 30 feet, the use of a Line

Driver output (output option HV or H5 in the Ordering Guide) along

with differential type receiver circuitry is strongly recommended. A

low capacitance twisted-shielded pair cable should be used whenever

using differential signals with cable lengths in excess of 30 ft. Contact

Customer Service for additional information. For high frequency

applications (>200kHz), this type of cable may be needed for all

lengths. EPC’s standard cable has a braided and foil shield, but it is not

twisted-shielded pair cable. Therefore, for high frequency applications,

it is highly recommended that the user terminate the standard cable

just outside the encoder, and then run a low capacitance twisted-

shielded pair cable the remaining distance.

Proper cable termination is also extremely important with differential

signals. You can try a simple, non-terminated configuration first.

However, keep in mind that signal reflections may occur, resulting in

severely distorted waveforms. For this type of signal distortion, parallel

termination is recommended, which involves placing a resistor across

the differential lines at the far (receiver) end of the line. This resistor

should be approximately equivalent to, or up to 10% greater than, the

characteristic impedance of the cable (Zo) [usually between 70-150

ohms]. This permits higher frequencies to be transmitted without

significant distortion. Unfortunately, low valued resistors can increase

the power dissipated by the Line Driver, and reduce the output signal

level. In this case, a capacitor should be placed in series with the

resistor. The capacitor value should be equal to the round trip delay

of the cable divided by the cables Zo. Round trip delay is equal to the

cable length multiplied by 1.7 ns/ft. (Note that the RC time constant of

this type of termination can reduce the system frequency response.)

A parallel termination resistor of a larger value than given above

can often provide adequate reduction of signal reflections, and still

maintain adequate frequency response with low power dissipation.

Experimentation in an application consisting of long cable runs will

usually result in the best balance of all of these factors.

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A common cause of signal distortion in systems is poor grounding. The

following tips will help eliminate distortions due to grounding:

1. It is extremely important that cable shields are connected to the

receiver/instrument (counter, PLC, etc.) ground.

2. Always make sure the motor/machine for which the encoder is

mounted is properly grounded.

3. The encoder case should also be grounded with the following

conditions:

a. DO NOT ground the encoder case through both the motor/

machine and the cable wiring.

b. DO NOT allow the encoder cable wiring to ground the motor/

machine exclusively. High motor/machine ground currents

could flow through the encoder wiring, potentially damaging the

encoder and associated equipment.

114

Technical Information

Ce opTion/Cable ConsideraTions

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