Other protects
① prevents stall to cross voltaic
is urgent when quickening, if asynchronous is dynamoelectric,dog logy, cross electric current to protect circuit movement, movement cannot) of proceed (stall. So, want to undertake controlling before load current is reduced, restrain frequency to rise or make frequency drops. To constant speed movement passes electricity mediumly, also have same control sometimes.
② prevents of overvoltage of stall second birth
The second birth energy of the generation when decelerate makes main circuit volts d.c. rises, protect a movement to prevent circuit of second birth overvoltage, want to undertake controlling before volts d.c. drops, restrain frequency to drop, prevent to cannot run (stall) .
3 transducer controls the of interference rejection measure of loop
because advocate of loop nonlinear (undertakes switch movement) , transducer itself is harmonic interference source, and its periphery dominates return circuit is loop of small energy, weak signal however, suffer the interference that other unit emerges extremely easily, cause transducer oneself and peripheral to cannot work normally. Accordingly, transducer is used in installation when, must take interference rejection step to dominating return circuit.
The of main control loop of 1) transducer
is the same as exterior undertake two kinds the basic loop of signal communication has imitate and number:
Loop of signal of electric current of ① 4 ～ 20mA (imitate) ; Loop of signal of voltage of 5V of ～ of 1 ～ 5V/0 (imitate) .
Loop of ② switch signal, a stop instruction of transducer, positive and negative turns the (number) such as the instruction.
Command signal of exterior control guides through afore-mentioned basic loop transducer, at the same time interference source also produces interference electromotive force on its loop, inbreak in order to control cable for media transducer.
The main type that 2) disturbs reachs interference rejection measure.
① electrostatic coupling disturbs: Accusation is made cable and all round the static capacitance coupling of electric return circuit, in the electromotive force of the generation in cable.
measure: Increase the space with interference source cable, achieve conductor diameter 40 when times above, interference pitch is not quite obvious.
installs screen conductor between two cable, again screen conductor ground connection.
② electrostatic induction disturbs: Point to all round the electromotive force that the magnetic flux change that electric return circuit produces gives in the induction in cable. The size be decided by of interference disturbs the magnetic flux volume that source cable generates, the opposite point of view between the closed circuit area that control cable forms and interference source cable and control cable.
measure: Will control commonly cable and advocate loop cable or laid of depart of other power cable, detached distance is in normally 30cm above (lowest is 10cm) , when detached difficulty, control cable crosses iron pipe laid. control conductor is wrung close, wring add up to span smaller, the course of laid is shorter, interference rejection effect is better.
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