전자부품 데이터시트 검색엔진 |
|
AD698AP 데이터시트(PDF) 5 Page - Analog Devices |
|
AD698AP 데이터시트(HTML) 5 Page - Analog Devices |
5 / 12 page AD698 REV. B –5– THEORY OF OPERATION A block diagram of the AD698 along with an LVDT (linear variable differential transformer) connected to its input is shown in Figure 5 below. The LVDT is an electromechanical trans- ducer—its input is the mechanical displacement of a core, and its output is an ac voltage proportional to core position. Two popular types of LVDTs are the half-bridge type and the series opposed or four-wire LVDT. In both types the moveable core couples flux between the windings. The series-opposed con- nected LVDT transducer consists of a primary winding ener- gized by an external sine wave reference source and two secondary windings connected in the series opposed configuration. The output voltage across the series secondary increases as the core is moved from the center. The direction of movement is detected by measuring the phase of the output. Half-bridge LVDTs have a single coil with a center tap and work like an autotransformer. The excitation voltage is applied across the coil; the voltage at the center tap is proportional to position. The device behaves similarly to a resistive voltage divider. A B AMP OSCILLATOR VOLTAGE REFERENCE A B FILTER AMP AD698 Figure 5. Functional Block Diagram The AD698 energizes the LVDT coil, senses the LVDT output voltages and produces a dc output voltage proportional to core position. The AD698 has a sine wave oscillator and power am- plifier to drive the LVDT. Two synchronous demodulation stages are available for decoding the primary and secondary voltages. A decoder determines the ratio of the output signal voltage to the input drive voltage (A/B). A filter stage and out- put amplifier are used to scale the resulting output. The oscillator comprises a multivibrator that produces a triwave output. The triwave drives a sine shaper that produces a low dis- tortion sine wave. Frequency and amplitude are determined by a single resistor and capacitor. Output frequency can range from 20 Hz to 20 kHz and amplitude from 2 V to 24 V rms. Total har- monic distortion is typically –50 dB. The AD698 decodes LVDTs by synchronously demodulating the amplitude modulated input (secondaries), A, and a fixed in- put reference (primary or sum of secondaries or fixed input), B. A common problem with earlier solutions was that any drift in the amplitude of the drive oscillator corresponded directly to a gain error in the output. The AD698, eliminates these errors by calculating the ratio of the LVDT output to its input excitation in order to cancel out any drift effects. This device differs from the AD598 LVDT signal conditioner in that it implements a different circuit transfer function and does not require the sum of the LVDT secondaries (A + B) to be constant with stroke length. The AD698 block diagram is shown below. The inputs consist of two independent synchronous demodulation channels. The B channel is designed to monitor the drive excitation to the LVDT. The full wave rectified output is filtered by C2 and sent to the computational circuit. Channel A is identical except that the comparator is pinned out separately. Since the A channel may reach 0 V output at LVDT null, the A channel demodulator is usually triggered by the primary voltage (B Channel). In addi- tion, a phase compensation network may be required to add a phase lead or lag to the A Channel to compensate for the LVDT primary to secondary phase shift. For half-bridge circuits the phase shift is noncritical, and the A channel voltage is large enough to trigger the demodulator. AD698 COMP ±1 FILTER B CHANNEL –BIN +BIN DUTY CYCLE DIVIDER A/B = 1 = 100% DUTY ±1 –ACOMP +ACOMP –AIN +AIN FILTER DEMODULATOR A CHANNEL A B OFF 2 OFF 1 BFILT1 BFILT2 C2 VOUT IREF 500µA V OUT FILTER C4 FB R2 C5 +VS –VS AFILT2 AFILT1 C3 V/I COMP V/I Figure 6. AD698 Block Diagram Once both channels are demodulated and filtered a division cir- cuit, implemented with a duty cycle multiplier, is used to calcu- late the ratio A/B. The output of the divider is a duty cycle. When A/B is equal to 1, the duty cycle will be equal to 100%. (This signal can be used as is if a pulse width modulated output is required.) The duty cycle drives a circuit that modulates and filters a reference current proportional to the duty cycle. The output amplifier scales the 500 µA reference current converting it to a voltage. The output transfer function is thus: VOUT = IREF × A/B × R2, where IREF = 500 µA |
유사한 부품 번호 - AD698AP |
|
유사한 설명 - AD698AP |
|
|
링크 URL |
개인정보취급방침 |
ALLDATASHEET.CO.KR |
ALLDATASHEET 가 귀하에 도움이 되셨나요? [ DONATE ] |
Alldatasheet는? | 광고문의 | 운영자에게 연락하기 | 개인정보취급방침 | 링크교환 | 제조사별 검색 All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |