Sin/Cos Sensors Overview


There are several varieties of Sin/Cos sensors that utilize different technologies, such as inductive, magnetic, or magnetoresistive. Regardless of the technology employed, Sin/Cos sensors produce a sine and cosine signal that corresponds to the rotor's angle. The motor drive can process this signal to determine the rotor's angle.





Figure 1. Sin/Cos Voltage and Angle Calculation 


Resolver vs Sin/Cos Sensors


Sin/Cos sensors share similarities with resolver sensors, as both ultimately convey angular position through sine and cosine signals. However, there are a few key distinctions:


  • Resolvers require an excitation signal: Unlike Sin/Cos sensors, resolvers need an AC excitation signal to operate, which is provided by the motor drive.
  • Resolvers do not require a power supply: They function using coils and magnetic coupling. You simply inject the excitation signal; no external power source is needed.
  • Resolvers require signal demodulation and level shifting: The sine and cosine outputs are modulated and can include negative voltages, which cannot be directly read by a microcontroller (MCU). Therefore, additional circuitry is needed to demodulate and shift the signals into a readable range.



Figure 2. Resolver Sensor I/Os and Signals



Sin/Cos sensors, on the other hand, provide sine and cosine signals that are typically centered around a fixed positive voltage,


Figure 3. Sin/Cos Sensor I/Os and Signals 



Selecting a Compatible Sensor: Key Criteria


There are several variations among Sin/Cos sensors. The selected sensor should meet the following criteria:


1. Signal Range


The signal should be centered around a positive voltage and remain within the 0 to 5 V range. While most Sin/Cos sensors center their signals at 2.5 V, this should always be verified, as Roboteq Sin/Cos motor drive inputs cannot accept voltages outside the 0–5 V range.


Figure 4. Sin/Cos Min/Max Values


2. Sin/Cos Cycles per Revolution


Some sensors provide more than one Sin/Cos signal period per full rotor rotation. The number of signal periods must be configured on the motor drive. The current parameter name for this setting is "SinCos/SSI Sensor Poles". However this label may be misleading as some Sin/Cos sensors use technologies that do not involve physical poles. What this parameter actually defines is the number of Sin/Cos signal periods per full rotor rotation, and it should be set accordingly.


Figure 5. Sin/Cos Sensor Number of Periods 


To ensure proper operation, the number of signal periods must not exceed the number of motor pole pairs. For example, if a motor has 5 pole pairs (i.e., 10 poles), the number of times the sine and cosine signals repeat during one full rotor rotation should not exceed 5. Exceeding this number would result in more sensor cycles than the electrical cycles required to drive the motor, making commutation impossible.



This condition also prevents the use of incremental Sin/Cos sensors, which function similarly to quadrature encoders and offer high resolution (e.g., 3600 Sin/Cos cycles per sensor rotation, often referred to as the sensor’s Resolution or PPR).


 

Finally, there is a type of magnetic Sin/Cos sensor that does not provide a fixed number of signal cycles per full rotor rotation. Instead, the number of cycles depends on the motor’s number of pole pairs, as the sensor derives its rotor reference from them. In that case, the sensor poles parameter must be set equal to the motor pole pairs.