Do RFID tags wear out?

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My spouse noticed recently that my home made cat feeder door was closing on Simone while she was eating when it should have stayed open, and has for 5 years or so.  She has been wearing the same RFID tag the whole time and we can hear her walking around when it clatters against her name tag on her collar.  I compared the tag with another one just like it and it seemed to have the same range, but I changed them out on her collar and now the door doesn't close while she is eating, so I have to assume the old tag was not functioning as well as the new one.  So I am a little confused.  Any ideas on this?

 

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I had a better picture of her name tag and RFID tag but you could read our phone number and apparently people scrub pictures on the web for phone numbers, and in fact captchas are often derived this way, so I just put a cute picture of her from two years ago.

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Tags 'should' never wear out as they have no moving parts or power sources in them if they are truly passive devices.  There are some tags that do have a coin cell in them.  Those tags were called SecureID and they were for Port Authority and other government use from back in the day, but I havent seen them in a long time.

 

It is possible that the tag suffered a static hit at some point and maybe that did it in.

 

JIm

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Jim's right: over many years, we have found very very few cases where RFID tags implanted within animals  fail to work. We *do* find that with time, a chip inserted at the shoulders can migrate within the body to a position where, while it still works, often appears to have very poor or intermittent range from the view of the door/feeder/whatever - it's simply further away. In such a case, a vet will often simply insert a second chip - but that has caused is issues with our latest software/hardware which has improved range over earlier versions and will cheerfully read both chips... so I've had to include code to handle that specific case.

 

That's not likely to be the case if you have a collar tag since it's external to the animal and constrained in position. Additionally, collar tags as a rule tend to have a much larger activating coil than internal chips and so have increased range - I recently tested a collar tag with over a half-metre detection range. However, I suppose it's possible that a collar tag could suffer damage to the coil?

 

Other thoughts: units returned to me for fault analysis (for short read range) tend to have circuit failure to some degree resulting in mistuning of the transmitter coil which can have a significant effect on range. Might be worth checking your transmit frequency; the tags can have rather a variable Q and might respond one better than another frequency.

 

But I don't think I've ever personally seen a chip that, once tested, has failed in service.

 

If you ping me a land mail address I'll be happy to send you a range indicator widget. It lights up when it sees a scan and will give you an idea of your transmit range. Batteries not required... Or I can send you the Gerbers and you can roll your own.

 

Neil

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Neil,

I am interested in your widget.  I will send you my address.  I did a range measurement with a home rolled transmit coil I have above my bench and the two tags appear to have the same range - about 18cm from transmit coil to tag.  The tag on her collar bangs and rattles against her name tag and I can see the tag coil move around inside the plastic tag body.  It is pretty big, maybe 2cm in diameter.  So I dont know what is going on.  All I really know is the feeder doesn't close in her face while she is eating like it was doing before I changed collar tags.  I thought I measured the transmit frequency the last time I had the feeder on my bench and it was close to 125kHz.

 

barnacle wrote:
We *do* find that with time, a chip inserted at the shoulders can migrate within the body to a position where, while it still works, often appears to have very poor or intermittent range from the view of the door/feeder/whatever - it's simply further away

 

Yes, I have seen the little tags migrate all over the place under cat's skin.  Sometimes almost to the "elbow"  Simone had two underskin chips when I got her from the shelter for some reason, and I can imagine all sorts of troubles if she got out and someone tried to scan her.  I know the two tags can interfere with each other.  If I hold 2 tags close together my system stops being able to get a value.  I assume the two tags are transmitting at the same time and the transmitting coil gets a jumble of bits from the two transmissions.

 

Is it possible the chips under her skin can interfere with the collar tag?  The collar tag is orders of magnitude larger that the ones under her skin.  Do they both operate at 125kHz?  I dont know anything about the chips under her skin.

 

barnacle wrote:
will cheerfully read both chips... so I've had to include code to handle that specific case.
 

 

How is it possible to separate the return from two tags?  Doesn't the encoding get all messed with return from two transmitters at the same time?  My system is old school.  It searches and waits for nine 1's in a row for the start and then reads the next 55 bits and does a Manchester decode.  If there are bits coming in from two sources, how do you separate them, or is that proprietary?  Now I am trying to think how I would do it.

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MarkThomas wrote:
How is it possible to separate the return from two tags? 

 

If they are on teh same 125Khz carrier you cannot.

 

MarkThomas wrote:
Doesn't the encoding get all messed with return from two transmitters at the same time? 

Sure does!!

 

MarkThomas wrote:
If there are bits coming in from two sources, how do you separate them, or is that proprietary?

 

You cannot.  Just like I replied in the last two sentences you cannot unscramble the two eggs.

 

 

Might I ask why you need to put a door on the feeder?  Is there another creature in teh place that would think nothig of emptying the feeder?

 

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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jgmdesign wrote:
Might I ask why you need to put a door on the feeder?  Is there another creature in teh place that would think nothig of emptying the feeder?

 

Yes, there is also Otis.  Otis has food allergies and is very docile, so we have to feed him special food.  Every meal requires that Simone likes the food in the feeder better than what Otis is getting or she will push him out of the way and eat his food.  He is not as aggressive and just stands close to her if he wants her food until she goes away, but the feeder door only stays open for 6 seconds after it stops detecting her tag and closes in his face.  He tries to stand in the same place and move in the same way as Simone, thinking he might be able to open the feeder because it opens when Simone does that.  He eats his whole bowl of food in one sitting, whereas Simone eats small amounts and comes back several times.  If he leaves anything in his bowl she will finish it off when he leaves just because.  Finding food that meets the flavor requirements and doesn't give Simone bloody poo and doesn't give Otis eosinophilic granulomas was a process that took a couple years, and was a problem when one of the foods we were using changed formulations and another got discontinued.  We have something now that works and were at wits end when the covid thing started and one of the foods became impossible to get, but now that the hoarding is over everything is good for the time being.

 

 

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Taking pictures of black cats is very difficult.  Everything blends together.  Here is one that was taken by a friend and entered in a contest that was titled "Mostly Black"

 

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Very Cool....On BOTH posts!

 

JIm

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Jim, Neil says he has code that will read both chips, so there seems to be a difference of opinion, or the implanted chips are different from the 125kHz ones we are used to.  I am trying to start a fight here.

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MarkThomas wrote:
Neil says he has code that will read both chips, so there seems to be a difference of opinion,

 

I would like you to quote where Neil wrote that. 

 

MarkThomas wrote:
I am trying to start a fight here.

 

So it seems....indecision

 

Jim

 

 

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Jim,

 

barnacle wrote:
In such a case, a vet will often simply insert a second chip - but that has caused is issues with our latest software/hardware which has improved range over earlier versions and will cheerfully read both chips... so I've had to include code to handle that specific case.

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Or maybe I misinterpreted.  My code just reads garbage with two tags, as you say.

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That does not mean that he can read two tags on the same frequency and unscramble the ones and zeroes.  I am guessing that he means that his code has a feature that does not cause it to 'crash' when he gets hit with this scenario.    Either way Neil is the only one who can answer this so I am not wasting my time guessing on what his meaning is/was.  Neil can answer if he so chooses tomorrow.  If he indeed has a way of unscrambling two tags coming in on the same reader I would bet there are  lot of interested parties out there that would love to know how he did it.  HID(one of the worlds biggest RFID makers)  would gladly pay to know how that worked.  I have yet to see a reader decode two tags with the same frequency presented at the same time.

 

 

You may be looking to start a fight, I certainly am going to avoid one.

 

 

Cya tomorrow. smiley

 

Jim

 

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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There was a thread not too long ago where ambulance workers could scan their whole toolbox with RFID to see what was missing.  All of the items in the toolbox had a tag.  But I believe that was a different kind of tag that allowed multiple simultaneous reads, although I dont know how that would work if they were all the same frequency, and I dont remember the resolution in that thread.  I dont know what kind of chips get implanted in cats.  I probably misinterpreted Neil's comment.

 

I guess a special case could be seeing the header bits (111111111) and then if the decode gave different garbage multiple times in a row it is the cat with two chips.  I understand your point, and after thinking about it for 5 seconds I agree with you, so I guess I can't start a fight.  We will have to see what Neil says about his special case.

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Years ago I worked on projects with RF tags and later rfid TAGS.

 

RF tags were made up of a coil and capacitor -- you could detect that a tag or tags was in the detection area -- but that's all.

 

RFID tags ( as the name implies) put out an identifier plus ( im our case) some security info. I think that they worked at 13.8 Mhz. They had a processor chip, but were externally powered. The system would generate a field of one frequency that would power the tag. The tag would generate an output on a slightly different frequency.  The system could read the information from multiple tags. Not ideaa exactly how that worked. 

 

Never worked with 125 Khz, but the name RFID does imply tags that can be distinguished from one another. Do they have a battery? I don't know.

 

Can they fail -- I'm sure. Possibly a connection is flaky and when the cat moves, the system loses the signal.  Something like that. If you got  your feline friend a new tag and it improves life that's a good thing. Maybe your feline friend will show you some gratitude, but probably not :)

 

hj

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ford2go wrote:
Never worked with 125 Khz, but the name RFID does imply tags that can be distinguished from one another. Do they have a battery? I don't know.

No, no battery.  The tag has a coil that charges a circuit that modifies the field produced by the transmitting coil, and the chip producing the field detects the change and reads the unique ID number of the fob.  That is how I understand it.

 

ford2go wrote:
Maybe your feline friend will show you some gratitude, but probably not :)

She seems happier if she can eat undisturbed, but other than that she doesn't show much gratitude.smiley

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Oh boy, can of worms...

 

Ok, quick primer hopefully without revealing company IP that I shouldn't... Disclaimer: I work for a company that produces RFID controlled cat flaps and feeders; that is owned by one of the largest producers of RFID animal tracking products and they are owned by a very large US drugs company. Anything I write here is *strictly* my opinion and not that of any of my employers.

 

There are, for domestic animals, a handful of competing RFID standards, all working at or around 125-135kHz. All transmit a single unique identifying code as long as they are in range of a sufficiently strong activating RF field of about the right frequency. They consist of an activating coil, around a ferrite bar for internal chips, and a tiny processor that can wake up when there's enough voltage induced in the coil. The processor transmits a single coded binary signal by shorting out its activating coil; that changes the impedance that the transmitter sees and this signal - volts to millivolts - can be detected by the transmitter.

 

The most common four types are FDX-A, FDX-B, Collar Tag, and Avid; somewhat less common is Trovan (Trovan supply FDX-B parts as well as their proprietary formats, I think). Each uses a different and non-compatible coding standard so the combination of chip type and serial number is sufficient to identify a unique part and therefore animal. In the UK and Europe, the most common type is FDX-B. We supply collar tags with all our products but we recommend that cats are chipped, not collared, to avoid any risk of the collar being trapped. (In the UK all dogs must be chipped by law). Information on the various types is randomly available on the internet; there is an ISO standard  https://en.wikipedia.org/wiki/IS...

 

Handling each chip type requires different software and different hardware signal chains (which obviously I can't discuss in detail) but when learning a new chip on a product, the process is to scan for a valid reading from each chip type in sequence; when you know what the chip type is, you need only scan for that type (saving both power and time) to make a go/no go decision on whether to release a door latch or open a feeder lid. A chip of a type other than that being scanned will cheerfully return data, but as it's not in the format you're expecting it will always fail to read a valid code.

 

Fundamental, as discussed above, is that you *can't* read two chips at the same time, whether they are the same type or different. They will stomp all over each others signal... but if one is in a stronger RF field, it will have more effect on the signal and often it is possible, perhaps with multiple attempts, to read that chip. Where a cat has two chips, it's likely that the second has been installed because the first has migrated and it will generally be further away; in most cases that's enough to read the intended chip every time. In good conditions, our hardware can often read a chip that is only an inch or two nearer than an interfering chip. 

 

But cats get themselves into odd positions. For the basic products, if a second chip is being read, all we can do is recommend trying to learn the animal multiple times. Hopefully one of those times the interfering chip will be read; at that point both chips are valid and the flap/lid will open for either. Learning the same chip repeatedly just rewrites the same table entry, so there's no risk of running out of animals - but it's a bit hit and miss. In Mark's case - very common, where each cat must eat its own diet and nothing else - we'd recommend that each has a dedicated feeder, with one cat learned to each.

 

However... we're all IoT these days, and now it becomes necessary to associate a particular chip with a particular animal so that e.g. its entrance and exit patterns or its feeding habits can be associated with it. Bear in mind that the whole point of the chip is to keep out unwanted (i.e. unlearned) animals, and there's a lot of clever logic relating to the various ways cats in particular interact. Allow this cat in, but close the lid *immediately* if any other chip is detected, or if another chip of the same type is detected, or train a new animal by leaving the lid initially open but closing it if another cat comes sniffing around... you get the idea. But the users want to see which cat is doing what, so the recent devices report activity to a server which talks to the user's phone app.

 

If you have two chips in a cat, when either might be detected, you simply need to associate both chips with the same cat. To simplify the server side we make that substitution in the device - it needs our people (usually me!) to tickle the internal data of the device to make the association and the result is that whichever chip is read, only the 'official' one is reported. This means that, for example, you can use a single feeder to track the feeding of two or more cats: if they arrive, eat, and leave at different times we can correctly assign the food eaten to a particular cat, even if they happen to have multiple chips. (If one cat starts to eat and is bullied out of the way by another, it's harder to make a valid assumption about who ate what but we can flag that it's happened; if that's what your cat does we recommend separate feeders (and possibly some custom modes to change the feeder's actions somewhat).

 

So my comment about 'can read two chips' was not intended to imply 'simultaneously' but rather 'can read one of two chips'... as mentioned above, it may take multiple read attempts before it works. Two collar tags on the same collar will likely never work; and an internal chip will almost always never be read in the presence of a collar tag.

 

Anyone still awake?

 

Neil

 

Last Edited: Sun. Jun 7, 2020 - 07:01 AM
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Hi Neil,

I am still awake, but not for much longer.  I'm pretty sure East Coast Jim is snoring loudly.  It is interesting you say your system scans through the various tag and chip types.  All of my stuff is pretty old, runs at 125 kHz and the tag number is Manchester encoded, so my question is is that FDX-A or Collar Tag, and do the two have different encoding?

 

mark

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Well, the 125kHz is pretty arbitrary anyway. Without looking at the source code comments I can't recall the details, but I have an idea that the FDX-B signal chain is used for Collar Tag. If it's an external device it should be a Collar Tag anyway.

 

Neil

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Thanks for clearing things up Neil

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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I am still mystified how they dont interfere with each other if one is louder, but I guess I can demonstrate that experimentally.  I started playing with this RFID stuff 10 years ago when I bought a cat door I wanted to modify from a flap to a sliding piece of Plexiglas that was pulled up by a stepper motor when my cat got her paw trapped in the flap like Chinese handcuffs.  I was just starting to learn electronics and bought an ATmega128 board from Futurlec and discovered AVRFreaks.  The door flap had an EM Microelectronic EM4095-1 chip driving the whole thing.  First I used the purchased cat door and hacked the signals to use the ATmega128 and a stepper motor.  Then I got more interested in RFID and bought 5 or 10 SOIC 16 pin EM4095 chips, some 2.7 mH 19 Ohm coils from a place in Australia that doesn't seem to sell them anymore, and a bunch of silver mica capacitors and made 4 perfboard circuits and figured out the decoding and implemented it the ATmega128.  Later I wound some of my own coils that were bigger and about 2.7mH.  One of the circuits I made has been driving a coil above my workbench for 10 years.  When it detects a fob an LCD display on the wall above my bench displays the date, time, and fob number.  So my bench has been continuously awash with 125kHz energy for 10 years and has probably had some effect on everything I have done in the past 10 years.  The clock chip has lost 17 minutes in the past 10 years.  For some reason the EM4095 chip in that circuit gets hot so I superglued a piece of copper to the top of it to disperse some of the heat.  The board I put in the cat feeder is another of the 4 I built and the EM4095 chip in that one runs cool.  I never figured out why some of them get hot and some of them run cool.  I know I was pretty proud of myself being a newbee to electronics and was able to make this all work.   Here is a picture of the circuit out of my lab book:

 

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I suspect that the company's founder took a slightly more complex approach - we use a couple of hundred components or more. But everything is very very carefully optimised - everything that that chip does we do in either dedicated hardware or software, and that's where we get the long range.

 

Neil

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Hey Neil,

That was what I was going to ask you.  I thought you probably do what that chip does yourself in hardware.  That kind of circuit design is totally beyond me.  I was pretty impressed with myself when I built that circuit I posted and was able to decode the signal in an ATmega.  Nowadays you can just buy a little box that does what I did for a few dollars.   What you guys are doing is way beyond impressive.  No wonder you won an award for it.  Getting 40cm range from the tiny chips implanted in cats still astonishes me.  It must make you pretty happy too.  Keep up the good work!

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We had some TAG/ID guys in many years ago (I think from some place called Scientific Generics & Dawar) , claiming their new tags could be bunched together with little trouble.  These were plain coil/chip tags, but they essentially waited some random time to respond, they also talked about tags that listen for a code and respond only under certain rules (like: any tag starting with 3, please respond, or if that generated collision garbage: any tag starting with 38, please respond).  So the whole process was formed as a smart search of some sort.  They waved around little handfuls of tags & it seemed to work, with all the tag numbers pooping up on the laptop.  Whatever was implemented, they claimed was "new and improved"  

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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Yeah, they're half duplex chips: they wait a random or programmed time after the energising signal stops before responding. More expensive and sometimes lower range than full duplex chips: all domestic animal stuff is full duplex.

 

Neil

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UHF tags can be clumped together and read from a distance of several metres. The electronics are a bit more expensive though. Price is decreasing.

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I remember that when I moved back to Denmark (from US) I had a dog with me, and was told that he would need a new chip because the tags used in EU was different.

But it also worked here so some tags can more than one standard.

 

If the two chips are the same the only way is to make the reader weaker (but closer if you can). so only one chip get energy to transmit. 

 

 

I still like this hack a coil and tiny85 and nothing else (no power etc) can make a id tag:

 

https://hackaday.com/2009/06/27/...

 

 

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Yes. There a  number of countries where it is a requirement to have a domestic animal chipped with the local preferred type when imported, whether or not it is already chipped. This is a pain.

 

Whether a reader can read different types of chip is down to the reader - i.e. does it understand the bitstream - but reading two chip is always a pain.

 

Neil