{"id":3555,"date":"2026-10-21T23:46:58","date_gmt":"2026-10-21T15:46:58","guid":{"rendered":"http:\/\/www.rsmdailynews.com\/blog\/?p=3555"},"modified":"2026-10-21T23:46:58","modified_gmt":"2026-10-21T15:46:58","slug":"what-types-of-position-sensors-are-used-in-switched-reluctance-motors-4afe-284792","status":"publish","type":"post","link":"http:\/\/www.rsmdailynews.com\/blog\/2026\/10\/21\/what-types-of-position-sensors-are-used-in-switched-reluctance-motors-4afe-284792\/","title":{"rendered":"What types of position sensors are used in Switched Reluctance Motors?"},"content":{"rendered":"

If you\u2019ve ever dabbled with Switched Reluctance Motors (SRMs) \u2014 or even just seen them work for EVs, industrial pumps, or renewable energy systems \u2014 you know they\u2019re tough, efficient, and way less finicky than your average permanent-magnet motor. But here\u2019s the thing: a good SRM is only as good as its position sensor. That\u2019s the secret sauce our team bangs on about every day as an SRM supplier \u2014 get this part wrong, and you\u2019re looking at messy torque ripple, wasted energy, or even stuck motors. Switched Reluctance Motor<\/a><\/p>\n

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Let\u2019s break down what position sensors we actually use for SRMs, why each matters, and how we pick the right one for a job. No overly technical jargon, I promise \u2014 this is the stuff we talk about over our morning coffee, not a college lecture.<\/p>\n

First off, let\u2019s level set: SRMs don\u2019t have permanent magnets on the rotor. That means the motor controller has to know exactly<\/em> where each rotor tooth is at all times to energize the stator windings at the perfect millisecond. Mess up that timing, and you get nothing but noise and lost power. So the sensor isn\u2019t just a \u201cnice-to-have\u201d \u2014 it\u2019s the eyes of the whole system.<\/p>\n

The OG: Hall Effect Sensors<\/h3>\n

If you\u2019ve been around motor tech for even a hot minute, you know Hall effect sensors. They\u2019re the first thing most people reach for when they need position sensing, and for good reason \u2014 they\u2019re cheap, tiny, and super reliable. How do they work for SRMs? Simple: we mount three Hall sensors on the stator housing, spaced 120 electrical degrees apart (same as the stator poles), and as the rotor spins, each tooth passes a sensor, which sends a tiny voltage pulse to the controller. The controller uses those pulses to figure out where the rotor is, when to flip the windings on or off, and how much torque to apply.<\/p>\n

We use Hall sensors for a ton of our lower-power SRMs \u2014 like small conveyor belts, light-duty pumps, and entry-level industrial automation. They\u2019re not perfect, though. If you have a high-speed motor, the pulses can get a little jittery, and they only give you discrete position points (you can\u2019t get super-precise, real-time position data between the sensor pulses). That\u2019s fine for a conveyor that\u2019s moving at a steady speed, but not so great for a 100kW SRM in an electric bus that needs smooth, fast torque changes. Also, they can be finicky if there\u2019s a lot of electrical noise from the motor itself \u2014 but we\u2019ve gotten pretty good at shielding the wiring to fix that.<\/p>\n

Resolvers: The Workhorse for High-Power SRMs<\/h3>\n

For our bigger, badder SRMs \u2014 think electric vehicles, wind turbine pitch systems, and heavy-duty mining pumps \u2014 we go with resolvers. If you\u2019re not familiar, a resolver is a rotary transformer that spits out two sine waves: one sine and one cosine, 90 degrees out of phase. The controller measures the amplitude of those waves and crunches the numbers to get the exact rotor position, way more precisely than Hall sensors.<\/p>\n

What\u2019s awesome about resolvers? They\u2019re basically indestructible. They can handle extreme heat, vibration, and electrical noise \u2014 all things you deal with in heavy industrial or off-road EV environments. We put resolvers on pretty much all our medium-to-high-power SRMs now, because their precision is non-negotiable. For example, in an electric delivery truck, you need super smooth torque to avoid jerking when the driver hits the gas, and resolvers give you that. The only downside? They\u2019re a bit pricier than Hall sensors, and you need extra circuitry to process the sine\/cosine signals, but for the performance you get, it\u2019s worth every penny.<\/p>\n

Encoders: High-Precision for Specialized Jobs<\/h3>\n

If you\u2019re working on something super precise \u2014 like a robot arm, CNC machine, or lab-grade test equipment \u2014 we use encoders. There are two main types here: incremental encoders and absolute encoders. Incremental encoders send a pulse every time the rotor moves a tiny step, so you can track speed and direction, but you lose your position if the motor turns off. Absolute encoders, on the other hand, give you a unique code for every single rotor position, even if the power cuts out. That\u2019s a game-changer for robotics, because you don\u2019t have to home the motor every time you turn it back on.<\/p>\n

We don\u2019t use encoders for every SRM \u2014 they\u2019re overkill for a simple pump \u2014 but when precision matters more than cost, they\u2019re our go-to. One of our clients makes surgical robots, and they needed an SRM that could move a tiny cutting tool with sub-degree precision. We paired a small SRM with a high-resolution absolute encoder, and it works like a charm. The only catch with encoders? They\u2019re more sensitive to dust and grime than resolvers, so we have to seal them up tight in applications where there\u2019s a lot of debris.<\/p>\n

Sensorless Options: When You Can\u2019t Fit a Sensor<\/h3>\n

Wait a second \u2014 what if you can\u2019t mount a physical sensor on the motor? Maybe it\u2019s too small, or there\u2019s no space, or cost is super tight for a disposable application. That\u2019s where sensorless control comes in. Instead of a physical sensor, the controller measures things like the current and voltage of the stator windings, and uses those readings to guess the rotor position. The basic idea is that the inductance of the stator windings changes as the rotor teeth pass by \u2014 when a rotor tooth lines up with a stator pole, inductance is high, and when it\u2019s not, it\u2019s low. The controller picks up on those inductance changes to figure out position.<\/p>\n

We\u2019ve been playing around with sensorless SRMs a lot lately, especially for low-cost, high-volume applications like small home appliances. The upside? No extra parts, simpler wiring, lower cost. The downside? Sensorless control is way trickier to pull off, especially at low speeds. If the motor\u2019s spinning really slow, the inductance changes are tiny, and the controller can\u2019t tell what\u2019s going on. Most sensorless SRMs we work with only work above 10-20% of their maximum speed, so you still need a Hall sensor to get the motor started (that\u2019s called a \u201cstart-up sensor\u201d). We call this hybrid approach \u201csensor-assisted sensorless,\u201d and it\u2019s been a huge hit for one of our clients making smart washing machines \u2014 they don\u2019t want a $5 sensor on every motor, but they need it to start smoothly.<\/p>\n

How We Pick the Right Sensor for Your SRM<\/h3>\n

As an SRM supplier, this is the part we get asked about all the time: \u201cWhich sensor do I need?\u201d The answer isn\u2019t one-size-fits-all, of course. Here\u2019s how we break it down for every project:<\/p>\n