Tham khảo tài liệu 'newnes sensor technology handbook 2005 yyepg lotb part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Chapter 15 These two signals are subtracted from each other by the error amplifier to yield an AC error signal of the form V siiuot sin0 cosọ - cos0 sinọ . Using a simple trigonometric identity this reduces to V siiuot sin 0 -ọ . The detector synchronously demodulates this AC error signal using the resolver s rotor voltage as a reference. This results in a DC error signal proportional to sin 0 - ọ . The DC error signal feeds an integrator the output of which drives a voltage-con-trolled-oscillator VCO . The VCO in turn causes the up down counter to count in the proper direction to cause sin 0 - ọ 0. When this is achieved 0 - ọ 0 and therefore ọ 0 to within one count. Hence the counter s digital output ọ represents the angle 0. The latches enable this data to be transferred externally without interrupting the loop s tracking. Figure Resolver-to-digital converter RTD . 390 Position and Motion Sensors This circuit is equivalent to a so-called type-2 servo loop because it has in effect two integrators. One is the counter which accumulates pulses the other is the integrator at the output of the detector. In a type-2 servo loop with a constant rotational velocity input the output digital word continuously follows or tracks the input without needing externally derived convert commands and with no steady state phase lag between the digital output word and actual shaft angle. An error signal appears only during periods of acceleration or deceleration. As an added bonus the tracking RDC provides an analog DC output voltage directly proportional to the shaft s rotational velocity. This is a useful feature if velocity is to be measured or used as a stabilization term in a servo system and it makes tachometers unnecessary. Since the operation of an RDC depends only on the ratio between input signal amplitudes attenuation in the lines connecting them to resolvers doesn t substantially affect performance. For similar reasons these converters are not greatly susceptible to
