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1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsTo turn a synchro or resolver’s AC signals into shaft-position data, use an input path designed for that sensor: a compatible synchro-to-digital or resolver-to-digital converter, a DAQ with suitable inputs or conditioning, or—if the hardware and software support it—analog capture followed by angle calculation. First match the sensor’s signal format, excitation voltage, and frequency to the acquisition hardware. A generic analog input is not automatically a resolver input.
How synchros and resolvers encode shaft position
Synchros and resolvers are transformer-type rotary transducers. An AC reference, or excitation, drives the rotor; stator windings return signals whose amplitudes vary with shaft angle. The two sensor types produce different signal formats, so their wiring and conversion paths are not interchangeable. North Atlantic Industries describes this operating principle in its SD Module Guide, dated August 3, 2026.
Resolver: sine and cosine signals
A resolver typically returns two secondary signals proportional to the sine and cosine of the shaft angle. A resolver-capable converter can use both signals, along with the AC reference, to determine angle. A DAQ approach must acquire and process the appropriate signals; sampling one winding as though it were a standalone DC position output will not recover angle correctly.
Synchro: three line-to-line stator signals
A synchro provides three line-to-line stator voltages whose relative amplitudes encode the shaft angle. Confirm that the converter or conditioning hardware supports synchro mode and the sensor’s actual wiring. A resolver input arrangement should not be assumed to accept synchro connections.
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Choose an acquisition path
The right route depends on the sensor, required dynamic performance, channel count, host system, and how much signal processing you want to own.
Dedicated tracking or sampling converter
A resolver-to-digital converter (RDC) or synchro-to-digital converter (SDC) is built to interpret the sensor’s AC reference and angle-encoded signals. Conversion designs include different principles: the Analog Devices handbook chapter Synchro and Resolver Conversion distinguishes tracking converters from successive-approximation converters. They are not simply generic ADCs applied to an arbitrary analog signal; their treatment of the AC reference and encoded angle is central to conversion. Compare tracking behavior, bandwidth, latency, and accuracy for the intended shaft motion rather than choosing on bit count alone.
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Resolver-capable DAQ input or conditioner
A DAQ platform may provide resolver-capable inputs or a dedicated conditioning module. In its May 8, 2024 KnowledgeBase guidance, NI describes several routes: PXIe-4340 resolver-capable inputs; the legacy SCXI-1540 conditioning option and examples; capable analog inputs with angle calculation in software; or a third-party resolver-to-digital converter connected to a DAQ counter channel. These are distinct system configurations, not a guarantee that any NI or other vendor analog input can accept a resolver directly. Check the exact module, driver, software, and platform compatibility; the SCXI-1540 is explicitly a legacy option.
Integrated system conditioner
An integrated conditioner can simplify acquisition when it matches the installed system. Curtiss-Wright’s MSRD-202A product page describes a module for its MEDAU-2000 or MCDAU-2000 systems. It accepts three-wire synchro or four-wire resolver position signals, digitizes position for PCM output, uses an external reference, and has two channels with selectable 10-, 12-, 14-, or 16-bit resolution. The page states system accuracy of 0.037% or 0.05%, depending on variant. These figures describe that product and ecosystem; they are not a general measure of what other conditioners achieve. Confirm the required DAU platform and current availability with the vendor.
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Direct analog capture and software conversion
Direct capture can be appropriate when the DAQ inputs, sampling, analog front end, and software are all capable of handling the resolver signals and excitation relationship. NI includes analog capture with software angle calculation among its resolver connection routes. The implementation still needs a valid method for conditioning and interpreting the sine/cosine signals; simply recording voltages does not by itself produce trustworthy shaft position. If the design instead places an RDC ahead of the DAQ, the converter’s digital output can be acquired through a compatible counter or other supported interface.
Match excitation and signal compatibility before wiring
Before selecting a module or connecting a sensor, compare its documentation with the sensor specification. Check the signal type and pinout, excitation source and reference arrangement, excitation voltage and frequency, and the input’s supported mode. NAI’s SD module family illustrates why the exact model matters: the family is divided into different voltage and frequency ranges rather than one universal excitation specification.
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| NAI module | Excitation frequency | Excitation voltage |
|---|---|---|
| SD1 | 47 Hz–1 kHz | 2–28 V RMS line-to-line |
| SD2 | 1–5 kHz | 2–28 V RMS line-to-line |
| SD3 | 5–10 kHz | 2–28 V RMS line-to-line |
| SD4 | 10–20 kHz | 2–28 V RMS line-to-line |
| SD5 | 47 Hz–1 kHz | 28–90 V RMS line-to-line |
These ranges are NAI family specifications in its August 3, 2026 guide, not a substitute for the manual for the exact module and sensor. A voltage or frequency mismatch can make a nominally compatible channel unsuitable. Also verify the reference source, required load drive, isolation, connector pinout, and whether the hardware is set for synchro or resolver input.
Compare performance and system fit
Resolution and accuracy are different specifications. Resolution describes the digital granularity available; accuracy describes how close the reported angle is to the actual angle under stated conditions. Dynamic behavior matters too: a converter may have a particular tracking rate, bandwidth, or data latency, affecting how well it follows a moving shaft. Ask for specifications and test conditions relevant to your motion, not just a headline number of bits.
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- Signal format and wiring: Confirm resolver sine/cosine pairs or synchro’s three stator lines, the supported mode, and the pinout.
- Excitation: Match voltage and frequency ranges, reference arrangement, and drive capability.
- Conversion performance: Compare specified accuracy, resolution, tracking behavior, bandwidth, latency or data age, and performance during motion.
- Channels and system integration: Check channel count, isolation, output format, host interface, operating-system and API support, and compatibility with the DAQ or data-acquisition unit.
- Environmental and application requirements: Verify that the module and wiring meet the application’s operating environment and safety needs.
- Two-speed sensors: Confirm channel pairing and configure the sensor’s coarse/fine gearing ratio; the method uses paired signals and can provide higher effective angular precision when the sensor system is designed for it.
What a custom resolver front end must handle
A custom resolver measurement board needs more than an ADC. It must generate and drive the AC excitation, buffer and condition the sine/cosine secondary signals, and process them to recover angle—and velocity if required. Texas Instruments’ resolver design article discusses MCU/PWM-and-filter and integrated RDC approaches, along with signal conditioning, phase lag, offsets, noise immunity, and resistor matching. It notes that a resolver primary can have low impedance and therefore require a high-current excitation driver.
TI gives example parameters for its particular resolver-based measurement design: 3–7 V RMS primary input voltage, 1–20 kHz excitation, 0.2–1.0 V/V transformation ratio, and ±25° phase shift. The article also gives an example system accuracy of ≤0.1° with 16-bit resolution. Those are design-specific example values, not universal resolver limits or a performance guarantee for every implementation.
For that article’s example 8.25 Vp-p excitation waveform at 20 kHz, TI calculates a minimum slew rate of 0.52 V/μs to avoid slew-induced distortion. That calculation applies to the stated waveform and frequency; a different design needs its own driver analysis. In general, evaluate drive current and slew rate, analog gain and matching, phase behavior, common-mode and noise performance, and application safety.
Quick Recap
Practical connection and selection sequence
- Identify the sensor: Read its documentation to determine whether it is a synchro or resolver, its wiring and signal format, excitation requirements, and whether it has coarse/fine outputs.
- Choose the conversion route: Select a compatible SDC/RDC, resolver-capable DAQ input or conditioner, or a documented analog-capture/software design. If using a converter before the DAQ, confirm the digital interface and counter or input compatibility.
- Verify excitation compatibility: Match voltage, frequency, reference arrangement, and required drive to both sensor and acquisition hardware before wiring.
- Check performance for the motion: Compare accuracy and resolution separately, then confirm tracking rate, bandwidth, latency, and behavior at the shaft’s expected movement.
- Confirm system details: Check channel count, isolation, output format, host software and drivers, environmental suitability, and platform support. For a two-speed sensor, verify paired channels and the configured gearing ratio.
- Validate the installation: Follow the specific sensor and module manuals for wiring and setup, then verify reported angle over the required range and motion before relying on the data.
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