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Glentek Inc., 208 Standard Street, El Segundo, California 90245, U.S.A. (310) 322-3026
SMA8105, SMA8205, and SMA8305 MANUAL
2.8 Tachometer (Velocity Mode) Feedback Options:
The following is a list of ways one can choose to implement tachometer feedback in order
to drive the motor through a velocity controlled servo loop:
•
Brush-type and brushless DC mechanical tachometer.
•
Simulated tachometer using the motor commutation signals (PSEUDO-TACH).
•
Sinusoidal resolver.
•
Simulated tachometer using the encoder signals.
The simplest way to simulate the actual velocity of the motor is by installing a mechanical
brush-type or brushless DC tachometer on the motor shaft which converts the velocity of the
motor into DC voltage.
The second method is to synthesize a digital tachometer using the motor commutation
signals (refer to section 2.6). The SMA8105 provides this option.
In the third method, with a sine/resolver amplifier (SMA8205) an analogue tachometer
signal is generated as part of the Resolver-to-Digital conversion process and is immediately
available for use thru the dip-switch options for velocity mode(S1-7).
The fourth method is to have an optical encoder installed on the motor shaft to determine
the direction and position of the motor as it runs. The incoming encoder signals are converted
into quadrature clock pulses. The frequency of this clock pulses changes with the velocity of
the motor and the up/down clock output signals change with the direction of which the motor is
running at. The frequency of the clock is then converted into the tach DC voltage signal using
the Frequency-to-Voltage converter.
2.9 Commutation Using Resolver:
The Resolver-to-Digital converter in the SMA8205 generates the necessary excitation for
the resolver, and converts the resolver’s sine and cosine signals into position data. This
position information is used to amplitude modulate the velocity error signal into three-phase,
sinusoidal and current-error signals like the one in section 2.5.
2.10 Current Mode in Sine/Resolver or Trapezoidal Amplifier vs Two/Three
Phase Input Current Mode Amplifier:
The fundamental difference between the current mode in sine/resolver or trapezoidal
amplifiers and the two or three phase input current mode amplifiers is that in the former case,
the commutation of the command and feedback signals is done within the amplifier itself. The
latter case accepts two or three 120
o
out of phase commutated drive signals. In other words,
the user’s controller has to do the commutation of the command and feedback signals
themselves. The user can either input two or three commutated drive signals. If the user has
chosen two phase input, the third phase is generated as the negative sum of the other two
inputs.
2.11 Protection Circuit:
The High- and Low-Speed Electronic Circuit Breakers(HS/ECB and LS/ECB) protect the
amplifier and motor from being damaged by high motor current(specified max. peak and rms
current values). The Over Temperature and Over Voltage detection circuits will shut off the
amplifier when the temperature of the amplifier or the buss(B+) voltage exceeds a specified
limit. Also, there are circuits which limit the motor from running in either or both directions.
