Hall Effect Sensors vs. Proxes
While doing some of the minor website maintenance tasks that you sometimes have to do when blogging, I came across a site called Alexa. I always wondered about search engine optimization (SEO) and how it works… this gave me a bit of a clue. Since I have two websites to maintain I typed both URLs into the site and surprise… the Automation Primer actually showed up! My other Automation Consulting, LLC site did not, but since its a work in process and its brand new I’m not too worried about that.
Anyway, one of the cool things about the Alexa site is that it tells you where your traffic comes from, what people were looking for when they found your site. I’ve always been curious as to how people got to my site if I didn’t tell them about it. Many of my hits come from Europe and Asia, for some reason especially India. (By the way, if you are reading this and you don’t know me personally, please comment or send me an e-mail telling me how you found the site… my curiousity is killing me!) Anyway, one of the biggest hits were from people searching for the following: “Is hall effect inductive or capacitive?” This seems like a somewhat misguided question unless you are just curious. But since this is one of the biggest hits on my site, who am I to question it? So here goes…
A Hall Effect sensor is really niether inductive or a capacitive, but it is closer to an inductive prox. For a great description of what the Hall effect is, just check out Wikipedia, which has a pretty good description. Essentially a hall effect sensor senses a magnetic field, whereas an inductive sensor creates its own magnetic field. Any current-carrying conductor creates a slight magnetic field of its own, transverse to the direction of current flow. The hall sensor creates a voltage difference based on the amount of magnetic field it senses, hence it is used to sense a magnetic object such as a magnet moving with a piston inside of a cylinder body. This makes it a great choice for end of cylinder stroke sensors since it can sense the magnet through a metal (typically aluminum) body.
An inductive prox uses an oscillator circuit to set up its own magnetic field. When a metal object large enough to absorb the field gets close enough, the oscillator stalls and the condition is sensed and used to switch a solid state device. So this is the fundamental difference between an inductive prox and a hall effect sensor. As far as a capacitive prox, this uses a plate that carries a charge. Any object with its own charge (which does not have to be metal at all…) will drive electrons off the plate and also switch a solid state device. Totally different application. Capacitive proxes are often used for sensing liquids through the side of a plastic tank or sensing a solid object such as your hand.
A better question might be when to use a Hall effect sensor or an inductive prox? Well, as I mentioned, since a hall effect senses the magnet inside of a metal body, it is a great choice for sensing end of stroke. Whenever possible however it is best to sense the actual tooling that is moving rather than the cylinder position; what if your cylinder linkage breaks? What if the magnet comes loose inside of the cylinder? This is actually somewhat common. When sensing a piece of metal tooling attached to an actuator the choice would be an inductive prox.
Asking the right question is often the most important part of engineering. Knowing what I have found about what people are searching for will hopefully allow me to tailor this site to search words. Other than the few comments I receive on this site I really have no idea how much meaningful traffic I get. This site does count the people who visit the site but it doesn’t say anything about who actually reads it. If you are reading this, please leave a comment just to let me know you read this far!
Admiring the time and effort you put into your website and detailed technical information on sensors you present here. It’s awesome to come across a blog every once in a while that isn’t the same old rehashed material. Fantastic read! I’ve saved your site and I’m adding your RSS feeds to my Google account.
A little feedback:
I came across your site via Gary Mintchell’s FeedForward. Please continue to keep it separate from your “commercial” site since there are way too few non-commercial automation blogs (BTW, I count magazines as commercial).
IIRC, you’re using WordPress, so you may want to check out the various available plug-ins. WP stats gives you some basic information include popular search terms, referring links, and where people go from your site. I know Google analytics are quite popular (and I’m pretty sure there are WP plugins for Google, too). Also, many hosting providers provide easy to install analysis software (IIRC mine provides AWStats, which I haven’t used).
Finally, there’s a lot more to the hall effect world than pneumatic limit sensors. Companies such as Melexis, austria microsystems, and Allegro Microsystems make some cool chips, with uses including:
— Measuring currents without using a shunt resistor
— Joysticks (CH Products’ superb hall effect joysticks use a Melexis chip)
— A pushbutton with precise stroke measurement (0-4mm of travel with analog output)
— Precise distance or angle measurement of a magnet relative to the hall effect chip
Thanks Tony. I will definately always keep this separate from my business site. I was surprised when I discovered that people were hitting this site from typing in in the query “Is a hall-effect sensor inductive or capacitive?” since I only had one post addressing proxes and hall effect sensors and it was a long time ago.
Interesting information on other uses of hall effect sensors. I have seen them used in joysticks and pushbuttons but didn’t know they would do angular measurements. I imagine there would have to be two sensors to calculate a difference?
Only one IC and one magnet is required; see, for example, the Melexis MLX90316.
BTW, another use is measuring speed by sensing gear teeth. If you want to explore, here are some links to part listings:
Melexis Hall Effect IC’s
Allegro Microsystems Products
austria microsystems magnetic encoders
A lot of these chips were designed for automotive applications, but could have many uses in industrial automation.
Thanks for the quick rundown on the differences between the two types of sensors. I typed a google query on “hall effect vs inductive sensor” to get a general idea on the different application. A vendor sent me a long spec sheet on a hall effect sensor and I wanted to know if I should invest the time to understand the details. For me the answer was no. The inductive proximity makes the most sense for my application, which is basically an RPM sensor.
Thanx. Another viewer from India. 🙂 Got here through google. I searched for “hall effect sensor vs proximity sensor” .
I did read the whole post. I was trying to find out the difference in the principle of operation of the two types of sensors. I’m a TA and one of my student’s popped the question during a lab session. From your post i understand that a hall effect sensor can only sense magnetic fields and so it cant be used to detect the presence of any metal object as in the case of an inductive proxy. Thanks again…
HI, thanks for the post. I am a viewer from South Africa.
I typed in the search: “hall effect vs inductive sensors”. The purpose for my search is to gain knowledge in order to decide which sensor I should use to sense 50 Hz signals (power frequency in SA) and have the output transmitted to Headphones for ‘listening’ to these signals. I am trying to figure out which sensor will give me the best audible performance, or if there will actually be a difference in sound quality…
I also see that Hall effect sensors are used in applications that require sensing of magnetic signals with frequencies over 100 kHz.
So there’s some info for your SEO analysis 🙂
Hello, I am from India and I was searching for hall effect sensor vs proximity sensor on Google and landed to this site. Anyways, I got a good overview my quarry from here.
Thanks a lot for the efforts for explaining. Keep it up..
Thanks for the help here. I am trying to replace a whiskey switch on parallel linkage with a proximity sensor. Want to be able to stick with a 2 wire set up sense the harnessing will be difficult to change. Helped me get an better idea of how the electrical current flows.
Just connect the outputs of the devices to the input. I assume you are using 24vdc, if so there should be no problem.
I meant whisker switch not whiskey switch
Hello, I am from Pakistan and I was searching for hall effect sensor vs proximity sensor on Google, I got a good overview my quarry from here.
Thanks a lot for the efforts for explaining. Keep it up.
Very good read. Thanks. I was searching for the difference between a hall effect sensor, prox switch, and a read switch(not sure if that’s an industry term or not) and this is what popped up thankfully.