Talk:Reed switch

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Patent lists and language[edit]

I find "patent claim" language very difficult to read and I don't think it's intended for the same purposes as "encyclopedia language". Patent claims use certain forms and conventions so that the patent has a good chance of standing up in court. An encyclopedia article should be considerably less stilted in tone.

I also find lists of patents to be incredibly dull and I doubt that one reader in 100 will run down more than one or two on the list. If the reader had the patience to work out how something works from reading dozens of patents, he wouldn't need an encyclopedia article at all! --Wtshymanski 22:57, 7 June 2006 (UTC)

I find them incredibly exciting and I figure that 66% of reader will run down more than one or two on the list (it is just a click away with the list there) if they want more information on this topic. USPatent

BTW, the list also has historical implicationd. It is a list of poeple that have improved the device! And the diagrams and images are nice. USPatent 14:30, 9 June 2006 (UTC)

Improve don't remove. 204.56.7.1

Patent language[edit]

Anyone can hit "reed switch" on a search engine and get the list of patents - so it seems pointless to merely list them all here without any summarization of why any particular patent is important. Certainly you'll have a hard time figuring out how anything works from patent langugage, which is intended to be vauge, extensible, and as inclusive as possible. Until someone can explain to me why each of these patents deserves to be listed in the article, I will continue to object to a willy-nilly list being dumped in. It's also bad form to copy from a patent claim, which a lot of the turgid description sounds like. For heaven's sake, write it in English! --Wtshymanski 02:15, 9 June 2006 (UTC)

Please stop removing the list. It is relevant content. Also, the patent language is clear and points out relevant information. You are deleting information about this item that is important, calling it unimportant ... don't delete all the information about every patent from the article, calling it unimportant. DO NOT DISRUPT WIKIPEDIA! just because of your POV (as stated on your User page and above header). It is good form to incorporate public domain content. United States patents are in the public domain, generally, and the information is relevant here. USPatent 13:39, 9 June 2006 (UTC)

BTW, don't de-highlight the title term, thanks. USPatent


Hey there![edit]

Oh wonderful. Cool picture borrowed from a patent, but now the opening paragraph is just plain WRONG. It's not the source of potential that attracts the reeds together, it's the applied magentic field. The very *essence* of a reed switch's operation is now missing from the lead paragraph. This is not an improvement. I haven't got time to fix this and I'm sore tempted to just revert back.

The patent list is NOT important - or at least not encyclopediac. A long list of primary sources without any commentary or summary or analysis is just worthless. I object to this padding of the article. --Wtshymanski 17:35, 9 June 2006 (UTC)

1st you read it wrong, but i changed it. The potenial diffence is not causing the movement, the leads are connected to it.

2nd the patent list is useful (further reading), relevant (innovation in the device), and historical (list the developments). Stop removing it and disruptively editing. USPatent 18:26, 9 June 2006 (UTC)

Hello again. The patent list is not useful. SUMMARIZE the developments and tell the reader, don't just say " Hey, go spend the next 4 hours waiting for .TIFFs to download 'cause I can't be bothered to tell you what the developments are!". Once again I object to the "big dumb list" school of Wikipedia article inflation. And just what IS a "close proximity"? As opposed to a "far proximity"? --Wtshymanski 20:13, 10 June 2006 (UTC)
If I were to ask you what a "watch" is, would you reply that it's a "configuration of gearwheels and escapement mechanism, said escapement disposed with a hairspring and antifriction pivot points, the whole assemblage encased in a metallic or other suitable impermeable container, the enclosure provided with a transparent portion through which one or more indicator pointers or wheels may be observed, the adjustment of the escapement set to provide a rythymic advance of the the mechanism at a temporal rate little influenced by exterior factors, the whole mechanism energized by a flat helical elastic metallic member." ? Or would you say "It's a small gadget for keeping time." ? Lead paragraph MUST be changed. --Wtshymanski 20:22, 10 June 2006 (UTC)
Agree 110% with Wtshymanski. — Omegatron 18:16, 28 July 2006 (UTC)

Should this be listed in list of patents?[edit]

Should this be listed in list of patents? It's in the category. Looked through the history and found this ...

Patents[edit]

1930s to the 1960s
1970s

Just a note ...

Either include the list or remove the category. thanks! J. D. Redding 03:49, 20 April 2007 (UTC)

Or alternatively, make a List of reed switch patents. J. D. Redding 03:51, 20 April 2007 (UTC)

How the reed actually moves[edit]

The article doesn't say how the magnetic reed actually moves. I mean, you can activate a regular normally open SPST reed switch with a N pole or S pole magnet (I think) and from any side of the glass envelope. What makes it uni-directional? A reed made of normal iron/steel won't do that.

Thanks. —Preceding unsigned comment added by DaveDodgy (talkcontribs) 13:58, 17 August 2009 (UTC)

MTBF/operation cycles[edit]

How many open & close cycles can a typical reed switch handle before it starts becoming erratic, or the contacts stick shut (or open)? Assuming no or little current passes through the contacts. Or perhaps the article could state that reed switches typically last from 5000 to 50,000,000 switchings (or whatever it is). —Preceding unsigned comment added by DaveDodgy (talkcontribs) 14:07, 17 August 2009 (UTC)

Hall effect sensor[edit]

My modificiation to include Hall effect sensor was erased, with the note that it's too far a field. The reason why I wanted to include it is to direct readers to the modern way of solving the same issues that mechanical reed switches were historically used for. From the article:

Uses

In addition to their use in reed relays, reed switches are widely used for electrical circuit control, particularly in the communications field. Reed switches actuated by magnets are commonly used in mechanical systems as proximity switches as well as in door and window sensors in burglar alarm systems and tamperproofing methods; however they can be disabled by a strong, external magnetic field. Reed switches were formerly used in the keyboards for computer terminals, where each key had a magnet and a reed switch actuated by depressing the key; cheaper switches are now used. Speed sensors on bicycle wheels use a reed switch to actuate briefly each time a magnet on the wheel passes the sensor.

Electric and electronic pedal keyboards used by pipe organ and Hammond organ players often use reed switches, where the glass enclosure of the contacts protects them from dirt, dust, and other particles.


Each and every one of these uses is more properly done by Hall effect sensors, that have faster reaction times, lower energy consumption and especially no moving elements to wear out. My bicycle speedometer is a Hall effect sensor. Using a reed switch that mechanically goes click-click each time the magnet on the spike passes by is crazy. Dollar tree has $1 burglar alarms or drawer LED's based on hall effect sensors. It's the modern and cheap replacement for a reed switch. I don't believe it's too far off of a field. Sillybilly (talk) 04:12, 7 October 2009 (UTC)

An encyclopedia article is not a tutorial on sensor design. A Hall sensor has a standing current - otherwise it can't detect a magnetic field. A reed switch detects magnetic fields without any current applied at all, consuming no energy. Reaction time is irrelevant for a keyboard or manual control. A moving element that lasts a million cycles might well do the job as well as a motionless device with indefinite life. Consider ESD immunity and power handling capability, as well. A reed switch can directly control such devices as a bell or buzzer, whereas a Hall device requires *something* to switch relatively high power signaling devices. --Wtshymanski (talk) 13:33, 7 October 2009 (UTC)
Those are good points. "Computers" and phone systems and pretty much all electric control equipment was based on mechanical relays and vacuum tubes back in the 1920-1950 era, but since 1970 solid state devices are more proper. While vacuum tube like devices are no longer used for general signal processing, and relegated to very high power or special applications, after all this time we still haven't been able to completely eliminate relays, they are still present in monitors for instance, because the very function of a relay is to use low power to switch high power. Power MOSFET's are recent non mechanical replacements for mechanical relays for things such as direct motor control, but they do have issues such as ESD, and limited power handling capacity. So where you need to switch a high power device and you end up using a mechanical relay anyway actuated by a hall effect sensor, a reed switch is more proper. But where a reed switch is used as a sensor, such as proximity detection, or rpm measurement, non mechanical things may be more proper.
Our argument goes along the lines of vacuum tubes vs. diodes and transistors. Yes there are applications where vacuum tubes are more proper, such as ESD immunity or power handling capacity, but in modern days, non mechanical solid state devices are better suited. From the Wikipedia vacuum tube page:
"For most purposes, the vacuum tube has been replaced by solid-state devices such as transistors and solid-state diodes. Solid-state devices last much longer, are smaller, more efficient, more reliable, and cheaper than equivalent vacuum tube devices. However, tubes are still used in specialized applications: for engineering reasons, as in high-power radio frequency transmitters; or for their aesthetic appeal and distinct sound signature, as in audio amplification."
"Vacuum tubes are less susceptible than corresponding solid-state components to the electromagnetic pulse effect of nuclear explosions. This property kept them in use for certain military applications long after transistors had replaced them elsewhere. Vacuum tubes are still used for very high-powered applications such as industrial radio-frequency heating, generating large amounts of RF energy for particle accelerators, and power amplification for broadcasting. In microwave ovens, cost-engineered magnetrons efficiently generate microwave power on the order of hundreds of watts."
Lacking the inclusion of such a paragraph about Hall-effect sensors, I still think the viewer should be notified about Hall effect sensors in a See also list. It is true that the advancement/difference between hall effect sensors and reed switches is not quite as stark as between vacuum tubes and transistors. For instance a vacuum tube uses lots of standby power to heat a cathode, compared to an FET transistor, as opposed to the case of reed switches using no standby power unlike hall effect sensors, so that aspect is not an advance. Also the cost of a reed switch and a hall effect sensor is about the same. There is something beautiful about the simplicity of design of a reed switch. But still, my Made in China bicycle rpm meter uses a Hall effect sensor, not a reed switch.
An encyclopedia is not a tutorial on sensor design, but a tutorial on general knowledge, a review of relevant topics to a field. The more effectively we can care for and teach the reader, the better. Sillybilly (talk) 04:35, 9 October 2009 (UTC)

Use in motors[edit]

Reed switches were used in motors to replace the commutator - and these were real products. As stated, they were rather short lived and superseeded by hall effect devices. I am trying to dig up a reference, but as always with obsolete technology, this is not always easy. What I do have in my possession is a tachometer that was recovered from a motor generator set. The motor shaft had a pair of magnets embedded in it (presumably 2 for balance) and the tachometer part used a reed switch to monitor the revolutions and display it on a digital display. I do know that the tachometer was in virtually continuous service for over fifteen years so fatigue failure does not seem to have been a problem. At 1500 R.P.M. that is a staggering 2.3E+10+ open and close operations. It was still operational when decommissioned. Some so called 'strength balls' use a similar idea (such as this one [1]). DieSwartzPunkt (talk) 18:36, 30 July 2012 (UTC)

A reference would be essential. A tachometer is not a brushless motor and those reeds could not have been switching any significant current. --Wtshymanski (talk) 18:44, 30 July 2012 (UTC)
The reed switches in the brushless motor did not switch significant currents either as the reed switches were used to operate additional circuitry in much the same way as the hall effect sensors do now. A reed switch could easily have switched a few ampéres directly in smaller motors, but it is doubtful that any would have operated this way as a pulse width modulated drive is used for maximum efficiency consistent with minumum power loss in the switching circuitry. Though not related to the types of motor that we are discussing, a simple direct switched reed switch motor can be found [here].
Attempts at digging up suitable references are proving difficult (as I thought they would due to the age od short marketing life). Most of the references I have found are describing motors where even the hall effect sensors have gone out of the window as they now rely on detecting the back E.M.F. from the windings themselves. I had a quick chat to an aeroplane modeler friend of mine, who quickly retrieved an old model aeroplane electric motor using reed switches (and the switches were a marvel of miniaturisation). Even armed with a maker and model number (Shing-Ho (Chinese perchance?) motor model HC-205 rated at 12 volts at 30 Amps), I cannot locate either the maker, the model or any information on line. If my friend still had the user manual at least I could have cited that. DieSwartzPunkt (talk) 15:42, 31 July 2012 (UTC)
If you have a manufacturer and exact model of motor that used reed switches, then why not use the manufacturer and model as a cite? You only need to prove that one example exists to disprove Wtshymanski's view that their existence is dubious. It should be noted that contrary to Wtshymanski's belief that because he has not heard of something, that it therefore cannot exist, many things probably do exist that he hasn't heard of. Problem is: that now he has declared it is dubious, he will hammer that view in regardless of facts or evidence. 86.150.65.44 (talk) 18:01, 31 July 2012 (UTC)
Well, ad hominem is one way of looking at it. On the other hand, I've knockd around the electrical business for a while, so I'm always delighted to find out something new. Another way of looking at it is that an editor who's tried to find references to the alleged practice can't find any. If one is going to insist on a positive statement of a fact on Wikipedia, one is usually obliged to find a reference for it if it is questinoed by other editors. We would be misleading Wikipedia readers if we led them to expect that reed switches are a routine part of brushless motors when the whole basis of the claim is one personal recollection of some undocumented and briefly-sold Chinese hobby RC model motor. I found a $20 bill in my shoe once, but I don't put that into the article on shoes or currency. --Wtshymanski (talk) 18:20, 31 July 2012 (UTC)
I do not believe that would meet the criteria for verifiability (WP:VERIFY). There is no evidence that the name on the motor is even the manufacturer. Rebranding of other manufacturer's parts is fairly routine in the far east, so I can't regard it as a verifiable reference. That these devices exist is not in doubt in my mind as I do recollect them from not so long ago (as well as having recently seen an example). Also, the editor who originally put the statement in the article also must have believed in their existence as the edit appeared to be a good faith edit. Prior to the development of Hall effect sensors, a reed switch system would be a fairly obvious development. I can only presume that it would have some sort of limit on the possible RPM, though the Shing-Ho motor was specified as 36,000 R.P.M. max, which I gather is in the right ball park for model aviation. I must agree with WTS. that some reference would be useful, so the claim should remain with the [citation needed] tag which might prompt someone else to come up with a suitable reference if I or WTS. fail to find one meantime. DieSwartzPunkt (talk) 13:21, 1 August 2012 (UTC)

──────────────────────────────────────────────────────────────────────────────────────────────────── It is undue emphasis on what must have been a rare technique to assert that brushless motors habitually used reed switches. I've looked at a couple editions of the McGraw Hill and Newnes handbooks for electrical engineers, I've searched Knovel for any description of brushless motors, and my local copy of Yeadon and Yeadon "Handbook of Small Electric Motors" doesn't mention it. It certainly wasn't "usual" and if these books don't mention it, I doubt it was ever very widespread if it existed at all. --Wtshymanski (talk) 13:35, 1 August 2012 (UTC)

That you fail to find any reference proves nothing. That you are unaware of any existence is enough evidence for you to decide that it connot possibly exist. As DieSwartzPunkt says, it is a perfectly logical development prior to Hall effect sensors coming into being. As he also points out, two people seem to think they did exist, so you are in the minority anyway (but as usual, you would never let that stand in the way of a good deletion). The suggestion is: that it was a short lived technique which may be why you have not heard of it (but then you clearly don't know how brushless motors work anyway as you assumed that the reed switches would switch the current directly). 86.150.65.44 (talk) 17:19, 1 August 2012 (UTC)
Of course these things existed. However until someone (anyone) stumps up a ref for them, policy is clear that they can be challenged, even if it's Wtshymanski raising the challenge. So he's just not wrong here. Andy Dingley (talk) 17:39, 1 August 2012 (UTC)
But why isn't anyone talking about them? And if I don't know how brushless motors work, how is our reader going to figure it out? --Wtshymanski (talk) 17:47, 1 August 2012 (UTC)
Well, Wtshymanski did put the [citation needed] tag against the claim. No problem there, it should have a reference. The tag might prompt someone else to provide one, which is all to the good. In my search, I did come up with something from a small pocket technical dictionary. It has the following rather terse entry.
Brushless DC Motor: A type of direct current motor where the commutator is replaced by a system that does not require physical electrical contact. This usually uses magnetic sensors such reed switches or hall effect devices.
Hmmm... Not overly abundant on detail. DieSwartzPunkt (talk) 17:32, 3 August 2012 (UTC)
WP electric motor articles are crap. And when they aren't, yet another Indian college student will be along to vandalise or 'fix' them until they are. BLDC in particular is far from good.
There are two forms of brushless motor. One is the fan type (low-noise, long-life, low-power), which began as commutator motors but then evolved reed and then Hall solid-state commutators for better service life. A development of these is the accurately controlled speed 'inverted pancake' motor used in disk and tape drives. A second type, with a quite separate history, are those that now form the majority of the BLDC article. These are broadly three-phase AC motors with permanent magnet rotors, driven from inverters. They have extremely high power in a small weight and volume - they're also high speed and noisy. The first of these had a free-running inverter, some may have use Hall sensing as a tachometer, but the tech these days is a free-running inverter for startup and low speeds, switching over to back-EMF sensing at higher speeds. Andy Dingley (talk) 19:56, 3 August 2012 (UTC)
In fact they have evolved even beyond that. The design now includes motors with a 'squirrel cage' or even wound type rotor (i.e. a 3 phase induction motor). These are particularly useful in applications where variable speed drive with high torque across the speed range is required. This can be achieved by varying the frequency of the inverter (ideally keeping the reactance of the rotor equal to its resistance at the slip frequency). These motors are now almost universal for traction purposes. However, they are about as far removed from a traditional DC motor as it is possible to get. The sole contribution of the DC is to power the inverter. DieSwartzPunkt (talk) 08:06, 5 August 2012 (UTC)
I should have added, that although they were traditionally noisy, that problem has now been solved with the introduction of the insulated gate bipolar transistor which is able to control the magnetic field much better and reduces the tendency of the field lines to 'snap' as the rotor rotates. Most people are unaware that most of the noise in any motor or generator is actually the oxygen in the air gap between the rotor and the stator 'twanging' as the field lines 'snap' (oxygen is magnetic). Very large machines are often run in hydrogen for cooling and the only noise is bearing and windage noise being otherwise practically silent. DieSwartzPunkt (talk) 08:19, 5 August 2012 (UTC)
I once owned an analogue X-Y-writer (EAI 1110 VARIPLOTTER MODEL 99.600), manufactured in 1963, which was originally part of an analogue computing setup and later in the 1980s hooked up to a Commodore CBM 4032 via a custom-made D/A interface. This plotter used two (2-phase?) 115V AC brushless servo motors for the movement of the pen arm in X and Y directions. The speed and direction of the movement was dictated by the amplitude and phase of AC error signals fed to the motors, which were generated by transistor-based measurement amplifiers. In order to achieve galvanic isolation, the X and Y DC input signals to these amplifiers were converted into AC signals and then fed through a set of transformers. This DC/AC converter was based on a reed-relay containing two reed-contacts with alternating contacts (no contact without current). I seem to remember that the coil to this chopper was driven by a 6.3V AC voltage in the kHz range, but it is also possible that it just worked with 50-60 Hz. Anyway, this electro-mechanical chopper was reliable enough to work over the some 30 years this plotter was in service. While the plotter had to go, I still have one of the motors and the service manuals with circuit diagrams. If it helps establishing some "unusual" usage of reed-contacts, I may look up more accurate details. --Matthiaspaul (talk) 21:05, 1 August 2012 (UTC)
Not quite the modus operandi that we had in mind, but interesting nevertheless. I suspect that it probably operated at the natural resonant requency of the reed switch would almost certainly be in the audio frequency range (matching your recollection). If you find those details, add it to the article. DieSwartzPunkt (talk) 17:32, 3 August 2012 (UTC)
The resonant reeds were known as 'vibrator' power supplies. We certainly warrant an article on those. Andy Dingley (talk) 19:56, 3 August 2012 (UTC)
Following up on the plotter topic, I looked up some specs. The pen and arm motors were actually (3-coil) 2-phase (6-lead) brushless AC servo motors, sized about 6 cm x 4 cm in diameter. There's very little resistance spinning the axis of this high precision-manufactured motor manually, it will take some 20 seconds before it stops again. Two of the coils were connected externally either in a 115V AC (parallel) or 230V AC (serial) configuration. From the service manual: "Motor, Servo, Pen(*) Drive (with Damper): 115V 60 cps, 2 phse, 3200 rpm, EAI No 270.492." The label on the motor itself reads: "Daystrom 60~ motor, Transicoil Division, U-208547, V∅1 115 / V∅2 230 SPT, RPM 2300, SIZE 15MA." (It's possible this stands for mA, at least this would match the thickness of the 6 leads.) The third coil was connected to the output transformer of the error amplifier. The electro-mechanical chopper on the terminals of the input transformer to this amplifier is specified as "Chopper: 6.3V 60 cps coil, DPDT BBM contacts, James Electronics, EAI No. B530 042 0." I could not find better specs. IIRC, it was cylindrical shaped and looked a bit like a fully metal-sheet-shielded tube. "DPDT" stands for dual-pole dual-throw contacts, but I'm not familiar with the meaning of "BBM". For curiosity, here's an excerpt of the EAI service manual describing the function of the pen/arm servo channels ((*) they are both identical electrically):
"The DC input signal is applied to the wiper of the chopper (after scaling through the plug-in network) and is compared to the potential at the center tap of transformer T1. This potential is the level taken from the pen(*) mandrel. Thus the potential difference between the chopper wiper and the center tap of Transformer T1 is directly proportional to the ordered and the actual positions of the pen(*). As the chopper wiper applies the input signal first at one end of the transformer primary and then the other at a 60-cycle rate, a 60 cycle AC error signal is generated on the secondary of T1. This 60 cycle error signal is in quadrature with the AC line phase and is generated by phase shifting the chopper drive voltage.
Note that the phase of the AC error signal is dependent on the polarity relationship of the mandrel voltage and the scaled input signal voltage. This phase relationship determines the direction the servo motor will turn. The AC error signal on the secondary of T1 is applied to the four stage amplifier mounted on the 6.473 Printed Circuit Card. The 6.473 Unit amplies the AC error signal to a level sufficient to drive the class B push-pull power amplifier consisting of Q1 and Q2 mounted on the 6.519 Chassis.
The push-pull power amplifier provides the necessary power to drive the servo motor. The common emitter configuration provides the necessary power with a minimum drain on the -24V supply. The push-pull stage is temperature compensated by a thermistor to minimize distortion and to prevent thermal runaway." (Of course, this works with 50 Hz as well.) --Matthiaspaul (talk) 18:32, 4 August 2012 (UTC)
Yes, but...a brushless AC servo motor is not a brushless DC motor. A chopper is not a reed switch. This article is about reed switches. --Wtshymanski (talk) 00:38, 5 August 2012 (UTC)
If you are going to be that pedantic, the actual motor part of most brushless DC motors don't run from DC either. DieSwartzPunkt (talk) 08:11, 5 August 2012 (UTC)
Well, you are correct. But as ever, this lengthy debate has sprung from your incorrect contention that reed switches were never used in motor applications. This is your standard technique. Display your usual lack of knowledge on a subject, then when a lengthy debate occurs, pointing out where you are wrong, lodge a protest at either the unwarranted length of the discussion or that it out of scope. 86.150.65.44 (talk) 14:51, 5 August 2012 (UTC)
Hm, obviously my example was about an AC motor, but I don't find this to be too much off-topic under a section header "Use in motors", except for, perhaps, that in the EAI example the reed-contacts are not physically located inside the motor compartment itself, but are part of the "driving circuitry".
(BTW. BBM stands for break-before-make.) --Matthiaspaul (talk) 21:22, 5 August 2012 (UTC)
I have a chopper from a plotter. It says "KACO CHOPPER CB1711/6,3 6,3V/20..200Hz Made in Germany". So not in kHz range but around the mains AC frequency. I also took apart another plotter and it had two more choppers, "ELLIOTT MINIATURE CHOPPER ELLIOTT BROS. LONDON LTD. PART NO 80175". All of these look like they are sealed inside a metal enclosure with epoxy seals. Sorry, no idea how they were connected.Olli Niemitalo (talk) 22:03, 27 June 2013 (UTC)

Circuit Symbol[edit]

I added a common symbol, since I was looking for it, but didn't find it here.

I don't know if it is a standard (as in IEEE whatever), but it seems to be a common, recognisable one.

It's the one I use anyways. Grahamatwp (talk) 11:42, 6 November 2012 (UTC)

Maximum switching frequency[edit]

Some info on typical maximum switching frequency would be great. — Preceding unsigned comment added by Proffiehenniedm (talkcontribs) 06:33, 5 February 2014 (UTC) https://en.wikipedia.org/w/index.php?title=Talk:Reed_switch&action=edit&section=11# — Preceding unsigned comment added by Proffiehenniedm (talkcontribs) 06:36, 5 February 2014 (UTC)

I just found some info at www.osdc.co.jp/jp/data/pdf/databook_en_2011.pdf in which a maximum frequency of 500 (Hz) is mentioned. I believe this is for a typical reed relais. Also high frequency types seem to exist, which will be able to switch at higher frequencies than 500 Hz.Wijsgrijs (talk) 22:16, 3 October 2014 (UTC)

Sensor category[edit]

Reed switch is in the switch category, but shouldn't it also be in the sensor category? How about the Magnetic device category? Tweisbach (talk) 09:13, 4 May 2014 (UTC)