Brainiacs...How Do Axle Counters Work ?

[Shedmaster]

Hi everybody,

 

Would anybody in the know be able to explain the basic principles of how axle counters work please?

 

I'm not after anything technical or that may be considered sensitive.

 

I have a mental picture of this trackside gadget, that sits and either counts axles as a train passes or physically detects the train in section by using a laser beam?

 

Many Thanks,

 

Kindest Regards,

 

Shed.

[Yardman]

Easier than that. It's a treadle that hits the wheel flange operating a microswitch. Look at the track near some level crossings.

[a98087]

Treadles work on a mechanical system, the flange pushes down arm, that breaks a contact and then makes a contact,

 

They have a small amount of hydraulic fluid in, which allows you to adjust the time that the arm takes to return to its normal position

 

There normally set for 7 seconds, but can be set for anything between about 2 and 30 seconds.

 

 

 

Axle counters works by making an electromagnet field, which is then interrupted by the metal wheel passing through, the electronic then registerd the amount of interferences and send this to a machine called an evaluator.

 

This is fed by axle counters as each end of a section, and when the count is 0 then the section is clear,

 

One evaluator can work with many sections, and you can share heads, so two adjacent sectiions only need 3 heads,

[phil-b259]

Treadles work on a mechanical system, the flange pushes down arm, that breaks a contact and then makes a contact,

 

They have a small amount of hydraulic fluid in, which allows you to adjust the time that the arm takes to return to its normal position

 

There normally set for 7 seconds, but can be set for anything between about 2 and 30 seconds.

 

Axle counters works by making an electromagnet field, which is then interrupted by the metal wheel passing through, the electronic then registerd the amount of interferences and send this to a machine called an evaluator.

 

This is fed by axle counters as each end of a section, and when the count is 0 then the section is clear,

 

One evaluator can work with many sections, and you can share heads, so two adjacent sectiions only need 3 heads,

 

To ensure the evaluator knows which way the train is moving (and thus whether to add or subtract axles) each track mounted head has 2 sensors built into it.

 

Each sensor continually sends back a signal to the evaluator that it is operating correctly - and for some 'clip on' types of sensor, that it is still attached to the rail. If these precise signals are not being received constantly the evaluator will go into fault mode and stay that way till reset.

 

Also the evaluator requires the electromagnetic field to be distorted in a very precise manor to register a successful count. Should this not happen the evaluator will again go into 'fault mode' and ensure the section is regarded as occupied by the signalling system.

 

In other words a mishandled p-way shovel may we'll fail an axle counter, but swinging it back again over the count head will do nothing to make things better - in fact it's more likely to more likely things worse.

 

For S&T testing dummy wheel profiles are used to check the response of the heads are in specification.

 

Should an axle counter be in said Fault mode then the signaller may attempt a reset. For this to be successful the last 'count' (or partial count) must be leaving the axle counter section rather than into it.

 

Furthermore even if the reset is successful and the section becomes clear then the protecting signal will still be held at Red until one train has successfully traversed the ENTIRE the axle counter section - (I.E. the evaluator must have seen 16 axles counted in and 16 counted out for example.

 

Thus where the fault was a partial 'count in' then TWO trains in succession must be cautioned through - one to restore the last action to a 'count out' and a second to remove the signal restriction.

 

If a possession is going to affect an axle counter section then some installations have buttons the signaller can operate called an EPR. This can only be operated if the axle counter section is proved clear BEFORE the possession is taken and all signals are at red. If successful, an EPR will allow the signaller to reset the axle counter section once the possession has been given up without the need to caution the first train through the section as in fault mode.

 

For treadles that require to be able to determine the directional movements twin arm versions exists. It should be noted however that Mechanical Treadles are NOT used with axle counters - they tend to usually be used in conjunction with AHB level crossings to instigate the crossing operation and to raise the barriers after the train has passed.

Edited April 12, 2018 by phil-b259

[iands]

Hi everybody,

 

Would anybody in the know be able to explain the basic principles of how axle counters work please?

 

I'm not after anything technical or that may be considered sensitive.

 

I have a mental picture of this trackside gadget, that sits and either counts axles as a train passes or physically detects the train in section by using a laser beam?

 

Many Thanks,

 

Kindest Regards,

 

Shed.

 

I'll post a couple of photos on here when I get home tonight, but essentially the axle counter head produces a magnetic field and when the flange of a wheel passes over the head it creates a disturbance. This disturbance is detected by an "evaluator" on the "entrance" to a track circuit and counts the number of disturbances "in". At the other end of the track circuit another axle counter head/evaluator counts the number of wheels (therefore axles) "out". Providing the two values tally, the track circuit then clears to show "unoccupied" on the relevant signal panel/VDU. Interestingly, I'm told that the axle counter actually counts "down", rather than up, e.g. from (I assume) "999" to 998, 997, 996 etc., etc., as each axle is detected, rather than counting up from "000" to 001, 002, 003 etc., etc. Why? I don't know off hand but perhaps one of the more knowledgeable signalling designers that frequent RMweb may be able to explain?

 

Regards, Ian.

[JeremyC]

Sounds as if the axle counter head is basically a proximity switch.

[phil-b259]

I'll post a couple of photos on here when I get home tonight, but essentially the axle counter head produces a magnetic field and when the flange of a wheel passes over the head it creates a disturbance. This disturbance is detected by an "evaluator" on the "entrance" to a track circuit and counts the number of disturbances "in". At the other end of the track circuit another axle counter head/evaluator counts the number of wheels (therefore axles) "out". Providing the two values tally, the track circuit then clears to show "unoccupied" on the relevant signal panel/VDU. Interestingly, I'm told that the axle counter actually counts "down", rather than up, e.g. from (I assume) "999" to 998, 997, 996 etc., etc., as each axle is detected, rather than counting up from "000" to 001, 002, 003 etc., etc. Why? I don't know off hand but perhaps one of the more knowledgeable signalling designers that frequent RMweb may be able to explain?

 

Regards, Ian.

 

Two important things here

 

Firstly the signaller DOES NOT get any indication of how many axles are in section  - All the signal interlocking (and thus the signallers display) is told by the axle counter equipment is whether the section in question  is clear or occupied (either by a train or due to a fault condition). As such it is perfectly possible to rip out a track circuit and put in an axle counter if you wished (or go back the other way).

 

Secondly the number of axles displayed on the front of the evaluator unit for the benefit of S&T techs ONLY is always a positive number - but it will indicate whether the last action was a 'count in' or a 'count out'. This is because the evaluator is not a 'dumb' bit of kit - it processes the axle counter inputs and deals with negative numbers behind the scenes...

 

Negative counts can occur due to the layout of count heads - which as I said earlier each head must contain 2 sensors within the one head so the direction of travel can be determined. Lets call these individual sensors SK1 and SK2 and imagine we have a bi-directional single line with a count head at each end of the section. Now lets consider a train moving in one direction, for example the 'UP' direction over the single line. As each wheel passes successively over BOTH SK1 and SK2 sensors in the count head at the beginning of the section the evaluator detects a 'successfully count' and increases the number of axles from 0 to 1. This process is repeated until we have lets say 16 axles in section. When the train reaches the other end of the section it again passes over an axle counter head with sensors again activated in the SK1 then SK2 order. Each successful wheel count starts bringing the number of axles back down to zero.

 

Now lets consider a train moving in the opposite direction - it will pass over the sensors in the reverse order (SK2 first then SK1). Depending on how you want to record it you can either start from zero, then increase using negative numbers (e.g. -1, -2, etc up to -16) OR if you imagine a 3 digit display it could go from 000, to -999, then -998, then -887, etc down to -984. It doesn't actually matter which way you like to think of it as neither number gets displayed to anyone what the evaluator DOES display is 16 regardless (the number of axles in the section) - which naturally always has to be a positive number.

 

If a genuine negative number situation presents itself - i.e. the axle counter believes it has zero axles within the section but then receives a valid 'count out' from a count head, it will automatically go into fault made - after all there is no such thing as the 'hand of god' on the real railway so such an action is either the WRONG SIDE FAILURE of a count head to see a 'count out' or someone has put a RRV (or similar on track halfway through the section - which MUST ONLY BE DONE UNDER A LINE BLOCKAGE).

Edited April 12, 2018 by phil-b259

[phil-b259]

Sounds as if the axle counter head is basically a proximity switch.

 

Yes, but a very sophisticated one. Think of it like a childs jigsaw box toy thing - if you are trying to put a piece through the star shaped hole then it has to be a star shaped piece to fit.

 

No different to certain types of track circuit that use the successful transmission of a very precise audio frequencies through the rails between transmitter and receiver rather than a basic voltage

Edited April 12, 2018 by phil-b259

[Oldddudders]

No different to certain types of track circuit that the successful transmission of a very precise audio frequencies through the rails between transmitter and receiver rather than a basic voltage

 

TI21?

[phil-b259]

TI21?

 

EBI tracks as they are now known in the trade.

 

Of course there are also Reed track circuits which are similar in principle

[APOLLO]

They also link axle counters to defect detectors in the USA.

 

 

 

And how they work

 

 

Anything similar in the UK ?.

 

Brit15

[phil-b259]

An example of an axle counter head (Frauscher)

 

https://www.bing.com/images/search?view=detailV2&ccid=LUBePHyC&id=D631AA53D44EDDE85963FFBAE805AB66228CF0A6&thid=OIP.LUBePHyC8Eb9vZo0ApN2BQHaE7&mediaurl=http%3a%2f%2fwww.advantageaustria.org%2fmp-images%2f10008.76609%2f10008.76609.500.500.jpeg-filenamefrauscher_bo1.jpg&exph=333&expw=500&q=frauscher+axle+counter&simid=608023713283116257&selectedIndex=8

 

An example of an axle counter 'brain' (Frauscher) - which in this case can be housed in a location case a good few Kilometres away from the head.

 

https://www.bing.com/images/search?view=detailV2&ccid=Kk06OKb%2f&id=30F7718B0D33D8DD5E32DBEF68A8925CB6E2AD21&thid=OIP.Kk06OKb_Ord4wFfZsTFdbQHaEK&mediaurl=https%3a%2f%2frailway-news.com%2fwp-content%2fuploads%2f2016%2f03%2fFrauscher-ACS2000-1920x1080px.jpg&exph=844&expw=1500&q=frauscher+axle+counter&simid=608055534671562452&selectedIndex=22

 

The evaluator cards have the numeric LED display on them, and on this particular type each card can handel TWO seperate sections (i.e. 2 track circuits in old money). The other thinner cards handle the individual sensor heads - again each card can deal with 2 sensor heads. Information is exchanged between cards via a data link within the enclosure. The cards themselves are totally interchangeable as the record of what does what is handeled by site specific coding in the enclosure (i.e. the card in Slot 03 will allways be AB sensor head for example)

 

Another manufacturers (AZLM) older style of count head - in this case the electrics associated with the sensors are located in the yellow 'mushroom'

 

https://www.bing.com/images/search?view=detailV2&ccid=QIbtT1Nw&id=96AC915E3DC8B26FF30B0A2E44788AF2B2ACA2EA&thid=OIP.QIbtT1Nw7JKXM4ODoxa7PgHaE8&mediaurl=https%3a%2f%2fupload.wikimedia.org%2fwikipedia%2fcommons%2f9%2f93%2fSBB_Axle_Counter_%25285714067212%2529.jpg&exph=2202&expw=3300&q=azlm+axle+counter&simid=608029734812781647&selectedIndex=5

 

The evaluators however are in a suitable location case - which could also be a few KMs away from the 'mushroom'

 

https://www.bing.com/images/search?view=detailV2&ccid=yxlks6OL&id=B7B7B2CD5DED6B4C78795F6AD3AFF32A227AF6A2&thid=OIP.yxlks6OLv3_f3jjxTXRpJwHaJl&mediaurl=https%3a%2f%2fimage.slidesharecdn.com%2fhandbookonmaintenanceofdigitalaxlecounter11-150208044503-conversion-gate01%2f95%2fhandbook-on-maintenance-of-digital-axle-counter-29-638.jpg%3fcb%3d1423370724&exph=826&expw=638&q=azlm+axle+counter&simid=608016716837294076&selectedIndex=24

 

As might be guessed from the manufacturers names, Germany seems to be the place folk have turned to when procuring these systems. Indeed with the AZLM type S&T techs were required to learn the exact meanings of 28 highly technical German words so as to diagnose faults on the system!

[phil-b259]

They also link axle counters to defect detectors in the USA.

 

Please do not confuse Hot Axlebox detectors or detectors designed to pick up things like wheel flats with AXLE COUNTERS used in signalling applications.

 

THEY ARE NOT THE SAME THING, NOR DO THEY SHARE ANY EQUIPMENT

 

The videos you have linked to seem to be describing the former, not the latter.

 

An example of equipment used in the UK to detect issues with rail vehicles themselves is the 'Wheelchex' system http://www.scot-rail.co.uk/page/WheelChex

 

Gotcha is another system used in the UK for the same purpose http://www.gotchamonitoringsystems.com/WDD.php

Edited April 12, 2018 by phil-b259

[iands]

Two important things here

 

Firstly the signaller DOES NOT get any indication of how many axles are in section  - All the signal interlocking (and thus the signallers display) is told by the axle counter equipment is whether the section in question  is clear or occupied (either by a train or due to a fault condition). As such it is perfectly possible to rip out a track circuit and put in an axle counter if you wished (or go back the other way).

 

Secondly the number of axles displayed on the front of the evaluator unit for the benefit of S&T techs ONLY is always a positive number - but it will indicate whether the last action was a 'count in' or a 'count out'. This is because the evaluator is not a 'dumb' bit of kit - it processes the axle counter inputs and deals with negative numbers behind the scenes...

 

Negative counts can occur due to the layout of count heads - which as I said earlier each head must contain 2 sensors within the one head so the direction of travel can be determined. Lets call these individual sensors SK1 and SK2 and imagine we have a bi-directional single line with a count head at each end of the section. Now lets consider a train moving in one direction, for example the 'UP' direction over the single line. As each wheel passes successively over BOTH SK1 and SK2 sensors in the count head at the beginning of the section the evaluator detects a 'successfully count' and increases the number of axles from 0 to 1. This process is repeated until we have lets say 16 axles in section. When the train reaches the other end of the section it again passes over an axle counter head with sensors again activated in the SK1 then SK2 order. Each successful wheel count starts bringing the number of axles back down to zero.

 

Now lets consider a train moving in the opposite direction - it will pass over the sensors in the reverse order. Depending on how you want to record it you can either start from zero, then increase using negative numbers (e.g. -1, -2, etc up to -16) OR if you imagine a 3 digit display it could go from 000, to -999, then -998, then -887, etc down to -984. It doesn't actually matter which way you like to think of it as neither number gets displayed to anyone what the evaluator DOES display is the number of axles in the section - which always has to be a positive number.

 

If a genuine negative number situation presents itself - i.e. the axle counter believes it has zero axles within the section but then receives a valid 'count out' from a count head, it will automatically go into fault made - after all there is no such thing as the 'hand of god' on the real railway so such an action is either the WRONG SIDE FAILURE of a count head to see a 'count in' or someone has put a RRV (or similar on track halfway through the section - which MUST ONLY BE DONE UNDER A LINE BLOCKAGE).

Thanks for the clarification Phil. I didn't make myself clear enough and apologies if I've misled anyone. I wasn't implying that the signaller got a "count" of every axle in or out, just an indication from the interlocking that the track was either occupied or clear. (Note to self - read what you've typed to see if it makes sense before hitting the "send" key).

 

Regards, Ian.

[St. Simon]

EBI tracks as they are now known in the trade.

 

Of course there are also Reed track circuits which are similar in principle

We still call them TI-21s on most occasions!

 

Simon

[iands]

I'll post a couple of photos on here when I get home tonight, but essentially the axle counter head produces a magnetic field and when the flange of a wheel passes over the head it creates a disturbance. This disturbance is detected by an "evaluator" on the "entrance" to a track circuit and counts the number of disturbances "in". At the other end of the track circuit another axle counter head/evaluator counts the number of wheels (therefore axles) "out". Providing the two values tally, the track circuit then clears to show "unoccupied" on the relevant signal panel/VDU. Interestingly, I'm told that the axle counter actually counts "down", rather than up, e.g. from (I assume) "999" to 998, 997, 996 etc., etc., as each axle is detected, rather than counting up from "000" to 001, 002, 003 etc., etc. Why? I don't know off hand but perhaps one of the more knowledgeable signalling designers that frequent RMweb may be able to explain?

 

Regards, Ian.

Although 'phil-b259' has beaten me to it in providing some photos of an Azlm type axle counter, I said I'd post some photos that I have - so here they are - from the East London Line project. 

 

 

Regards, Ian.

[Edwin_m]

Two important things here

 

Firstly the signaller DOES NOT get any indication of how many axles are in section  - All the signal interlocking (and thus the signallers display) is told by the axle counter equipment is whether the section in question  is clear or occupied (either by a train or due to a fault condition). As such it is perfectly possible to rip out a track circuit and put in an axle counter if you wished (or go back the other way).

 

Secondly the number of axles displayed on the front of the evaluator unit for the benefit of S&T techs ONLY is always a positive number - but it will indicate whether the last action was a 'count in' or a 'count out'. This is because the evaluator is not a 'dumb' bit of kit - it processes the axle counter inputs and deals with negative numbers behind the scenes...

 

Negative counts can occur due to the layout of count heads - which as I said earlier each head must contain 2 sensors within the one head so the direction of travel can be determined. Lets call these individual sensors SK1 and SK2 and imagine we have a bi-directional single line with a count head at each end of the section. Now lets consider a train moving in one direction, for example the 'UP' direction over the single line. As each wheel passes successively over BOTH SK1 and SK2 sensors in the count head at the beginning of the section the evaluator detects a 'successfully count' and increases the number of axles from 0 to 1. This process is repeated until we have lets say 16 axles in section. When the train reaches the other end of the section it again passes over an axle counter head with sensors again activated in the SK1 then SK2 order. Each successful wheel count starts bringing the number of axles back down to zero.

 

Now lets consider a train moving in the opposite direction - it will pass over the sensors in the reverse order (SK2 first then SK1). Depending on how you want to record it you can either start from zero, then increase using negative numbers (e.g. -1, -2, etc up to -16) OR if you imagine a 3 digit display it could go from 000, to -999, then -998, then -887, etc down to -984. It doesn't actually matter which way you like to think of it as neither number gets displayed to anyone what the evaluator DOES display is 16 regardless (the number of axles in the section) - which naturally always has to be a positive number.

 

If a genuine negative number situation presents itself - i.e. the axle counter believes it has zero axles within the section but then receives a valid 'count out' from a count head, it will automatically go into fault made - after all there is no such thing as the 'hand of god' on the real railway so such an action is either the WRONG SIDE FAILURE of a count head to see a 'count out' or someone has put a RRV (or similar on track halfway through the section - which MUST ONLY BE DONE UNDER A LINE BLOCKAGE).

I'm remembering back to a BR Research project I will slightly involved in as a graduate trainee, where they wanted to make the SSI do the job of the evaluator and develop software and a special trackside module that would interface directly to the sensor.  This was part of an attempt to reduce the cost of signalling on secondary routes that were too busy for RETB but not remunerative enough to justify re-signalling with full-spec SSI.  Obviously it came to nothing, though I don't know why, or you could say it was just ahead of its time like many Research projects. 

 

My vague recollection of that system is that each sensor would normally be part of two sections, say AA and AB.  Each section would have a register of the number of axles in that section, and would report clear only if that value was zero.  A wheel passing from AA to AB would decrement the stored count of axles for AA and increment it for AB, so (in that system at least) the count could never go negative (this would have been a fault state as noted above).  A single section could have more than two sensors to account for areas of pointwork, which obviously would have to be configured so the system knew which was was "in" and "out". 

Edited April 12, 2018 by Edwin_m

[mark axlecounter]

We Have them at Horrocksford and Daisyfield and they are a goot bit of kit when working correctly but its a nightmare when they go wrong.  

As most people have said they count the axle/ wheel going in and then out either the same way or the other end using the sensors on the web of the rail. The ones at horrocksford were installed because we had an IB signal put in (intermediate signal ) so we can regulate trains better. 

 

Mark

[Shedmaster]

Hi,

 

As ever, Thank You for your interesting and detailed responses, I'm reading these with interest.

 

iands, your excellent pictures have thrown up another question now, what do those yellow things do in the middle of the concrete sleepers? Movement detectors? Anchors?

(Sorry Shed, hijacking my own thread !)

 

Kindest Regards,

 

Shed.

[The Stationmaster]

Well over a decade ago I was sent off as a sort of 'guinea pig' to carry out simulated user testing of a new signalling control work station using the screens and desk equipment which would be going into the signalbox concerned but working through a test rig which totally simulated the interlocking as well as train movements plus various faults.  The truly frightening thing of this basically US designed kit was that as a 'Signalman' I found that I could reset entire groups of axle counters with nothing more needed than two clicks of a mouse button (plus entering a fault code on the system log).

 

It amazed me that something so dangerous could be done so easily without actually requiring on-ground equipment to be checked and tested - all I needed to do was log a fault code - and then two clicks of the mouse button.  I was somewhat scathing in my comments about this feature and an ergonomics expert from our company who was monitoring my 'work' was as amazed as I was - and she wasn't a railway operator.  The system underwent a number of modifications before it went live at site - looking back on the 'net it was commissioned in 2003.

[iands]

Hi,

 

As ever, Thank You for your interesting and detailed responses, I'm reading these with interest.

 

iands, your excellent pictures have thrown up another question now, what do those yellow things do in the middle of the concrete sleepers? Movement detectors? Anchors?

(Sorry Shed, hijacking my own thread !)

 

Kindest Regards,

 

Shed.

Hi Shed,

 

Yes,the yellow things are sleeper ties, or anchors if you prefer. They are used to help stop lateral side-ways movement of the track on curves.

 

Regards, Ian.

[Ncarter2]

Hi Shed,

 

Yes,the yellow things are sleeper ties, or anchors if you prefer. They are used to help stop lateral side-ways movement of the track on curves.

 

Regards, Ian.

Known as LERP’s. They are used as above but they are also used around bridges with embankment issues in which the track can slip over time. We have used them in conjunction with ballast gluing for this reason. There is a different version that goes on the sleeper ends, mainly used in timber they can be used on some pre drilled concretes.

The bonus with the new ones are you only need loosen the screw on the top and they then become free to allow for tamping etc, no need to fully remove.

[Shedmaster]

Hi,

 

So, real life track pins eh? Who'd have thought it.....

 

So, getting back to the axle counters then, these are totally different 'heads' to those used for HABD's etc? Again, I'm just curious as to how they count axles and know the difference between an axle and a part of the bogie/undergubbins.

 

Many Thanks,

 

Kindest Regards,

 

Shed.

[jim.snowdon]

Known as LERP’s. They are used as above but they are also used around bridges with embankment issues in which the track can slip over time. We have used them in conjunction with ballast gluing for this reason. There is a different version that goes on the sleeper ends, mainly used in timber they can be used on some pre drilled concretes.

The bonus with the new ones are you only need loosen the screw on the top and they then become free to allow for tamping etc, no need to fully remove.

But something of a pain to install?

 

Jim

[phil-b259]

 

So, getting back to the axle counters then, these are totally different 'heads' to those used for HABD's etc? Again, I'm just curious as to how they count axles and know the difference between an axle and a part of the bogie/undergubbins.

 

Many Thanks,

 

Kindest Regards,

 

Shed.

 

Because they DON'T count axles!

 

If you look at the pictures / links we have put up so far its clear that the sensor is designed to detect the passage of WHEELS - or more specifically the FLANGE of a wheel which has to be of a certain profile and thus distorts an electromagnetic field in a very precise way.

 

Axle counters are called that because every wheel is connected to an axle, and each axle technically has two wheels, thus having a wheel sensor only on one rail can never perform an accurate count of the number of wheels in section.

 

As for systems designed to pick up wheel defects - these are looking more at vibration and loading in the rail, temperatures of passing vehicles etc and are basically designed to monitor totally different parameters compared to am axle counter count head.

Edited April 14, 2018 by phil-b259