PDS Design T1689 Technical Manual Rev 07
Encoders & Encoder Cables MV3000 Air Cooled DELTA
Page 104
Outside the drive enclosure, the motor cable must be segregated from other cables by at least 300 mm (12 in).
In the case of some types of screened/armoured cable, the cable screen/armour is not acceptable as a
protective earth conductor. This is usually when the screen/armour has a low cross-sectional area. In such
cases, the following points must be noted:
• If the cable has only four internal cores, do not use the fourth core as a protective earthing
conductor. The unequal magnetic coupling from this core to the other three cores would result
in a voltage being induced into the protective earthing conductor. This voltage will then cause
nuisance currents to circulate in the cable screen/armour or in the external installation. If this
type of cable is used, use a protective earth conductor external to the screened/armoured cable.
• If the protective earth conductor is run inside the cable, a symmetrical cable must be used. This
is a cable which contains three protective earth conductors equally distributed inside the cable.
Such cables are marketed as “VFD cables”. The purpose of this is to ensure that magnetic fields
inside the cable do not induce unwanted currents into the protective earthing system of the
installation. All three protective earthing conductors must be bonded to both the drive cubicle
and the motor.
• If the screen/armour of a cable with internal protective earthing conductors is bonded at both
ends, the screen/armour terminations must be capable of handling any residual circulating
currents that are induced by the internal protective earth conductors.
• If the screen/armour of a cable with internal protective earthing conductors is bonded at one end
only, the shielding effectiveness of the cable at radio-frequencies will be reduced. This could
cause problems in installations with low radio-frequency emission limits.
4.3 ENCODERS & ENCODER CABLES
4.3.1 Encoder Selection
Only encoders having RS422A output (A/B/Z) can be used (a marker pulse is only required when using the
drive's position controller).
The MV3000e is equipped with two power supplies to power various encoders, which may be used. There are
two acceptable types of encoder:
• Encoders requiring +5 V supply and producing RS422A output.
For these encoders use TB5/4 (+5 V) to supply them and in cases where long cable runs cause a
supply volts drop to the encoder, parameter P13.06 will allow this supply voltage to be adjusted
between +4.5 V to +6.5 V. Refer to the guided commissioning charts in the Commissioning
section of the appropriate Getting Started Manual for details. If the sense wires are connected
(FB+ and FB–) at the encoder end of the cable, the MV3000e will automatically adjust the
encoder supply accordingly.
• Encoders requiring +24 V supply and producing RS422A output. For these encoders use TB5/6
(+24 V).
Encoders requiring +24 V supply and producing 24 V differential outputs are NOT compatible with the
MV3000e controller, the pulse train must be RS422A.
4.3.2 Encoder Resolution
For accurate speed control, especially at low speeds, a resolution ("line count") of no less than 1024 pulses per
revolution is suggested.
There are two limits on the maximum line count for the chosen encoder. The line count must comply with
both of the following conditions:
• The line count must be less than or equal to 64 000 pulses per revolution (due to the drive
software).
• The time delay between an edge on encoder channel A and an edge on channel B must be
greater than 333 ns at the required top speed of the motor.
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