How would I measure RPMs in a diesel engine? - Page 1
Forum section: electronics / beginners

author: gregoryfenton
author_rank: Newbie
timestamp: October 07, 2013, 12:27:17 am
content: Hi allMy current project is a good one (details will come later but it's something I am proud to be involved in) has several devices being monitored via a microcontroller - udoohttp://www.udoo.orgin this case, I opted for the quad core.One of the tasks is to measure the RPM of a diesel engine. What would you guys suggest as to the best way to accomplish this?My opinion is to go for a magnet mounted on the flywheel and a reed switch to count pulses, would this work?Comments and suggestions are more than welcome

author: the nerdling
author_rank: Newbie
timestamp: October 07, 2013, 12:44:12 am
content: instead of the reed switch use a hall effect sensor, the reed switch would wear out and not be as accurate because of the movement

author: Dave
author_rank: Super Contributor
timestamp: October 07, 2013, 12:44:58 am
content: I wouldn't put anything on the axle itself. Instead, I would put a magnet on top of a hall effect sensor and fix that above the teeth of a spinning gear. The teeth moving in front of the magnet+sensor assembly would cause the magnetic field to fluctuate and you would see that on the output of the hall sensor.

author: Toble_Miner
author_rank: Contributor
timestamp: October 07, 2013, 12:52:23 am
content: Hi,QuoteThis would probably work but it would put some imbalance to your flywheel. You should at least use two magnets, one on each side of the flywheel. Also if you have a really high rotation speed it might be very difficult to balance the flywheel with the magnets.In my opinion using some kind of a disk mounted onto the shaft of the engine with one or more slits in it and a light barrier shining through those slits once each turn of the engine is a much better idea.TobiasP.S. Please excuse my maybe quite rusty English. I'm from Germany and didn't write any Engish text for quite a while now.

author: Mr Smiley
author_rank: Frequent Contributor
timestamp: October 07, 2013, 01:05:29 am
content: Info on reed switcheshttp://www.biltek.tubitak.gov.tr/gelisim/elektronik/dosyalar/31/reed.pdfHow there madeYou may, at high speed have contact bounce problems.Probably better off with a magnet and hall sensor or a slotted opto, if your going to connect to something that does say up to 5,000rpm then the lighter the item connected to the rotating shaft the better.

author: Dave
author_rank: Super Contributor
timestamp: October 07, 2013, 01:08:17 am
content: Quote from: Toble_Miner on October 07, 2013, 12:52:23 amUnreliable. The engine bay is not a clean environment, the light sensor will get dirty and you will lose your signal.

author: victor
author_rank: Regular Contributor
timestamp: October 07, 2013, 01:37:54 am
content: Optic SensorYou can use a reflective adhesive tape and optic sensor so it does not add weight to the shaft.You can do it using dark or light strips, you can do the threshold in software if your adc is fast enough or you can use discrete logic to do that and feed a digital pulse/clock to your micro controller.Watch at 2:00This will work to KHz range, but be aware of if it get dirt it may stop working, so you may need to enclosure it.If you use infrared, be aware that hot metals may emit infrared it can affect your low threshold.Hall-effect sensorOr use hall effect sensor, computer fan use it as a tachometer, some fans goes as fast as 5k RPM and AFAIK this will cover the range of most diesel engines.Steel is magnetic so you can predict some challenges you may encounter.BrushYou can use kind of brush like used on DC motors, but it will have limited life, but it is easy to set up and cheap.

author: NDT
author_rank: Contributor
timestamp: October 07, 2013, 01:43:40 am
content: Hello Gregory!I'd rather go with a hall effect sensor counting the teeth on the flywheel or a magnetic pickup (coil magnet, essentialy the same). At least that's how everybody is doing it today (that doesn't mean it's the right way to do it, but you have a huge line of sensors to choose from). I've seen optical measurement on some Nissan engines too, but it's not really used. I've been in the EFI (electronic fuel injection) world for quite some time, and I've never seen a successful development using a method other than what I've just written. Besides, you get expandability, because you could measure TDC (top dead center) position if you make a notch or a recess on one of the teeth in such a way that the sensor doesn't react to that particular tooth. If you don't want such a huge resolution, you could attach the sensor to the injector pump, and with the crankshaft/pump pulley or gear ratio, it's easy to know the RPM.In a diesel engine, I see that the vibrations will be a major enemy of the reed switch setup you proposed. I don't know if it will affect the measurement, but no moving parts is always better!Some words about the two types of sensor I just described...Hall Effect: doesn't require heavy signal conditioning, it delivers a constant voltage pulse regardless of the RPM, it's very easy to use, but it relies on theHall Effect, so you need magnetized teeth or a "trigger wheel", which is a disc with a number of teeth on the edge. It also needs a power source, usually +12V or +5V, but produces also a square +12V or +5V pulse.Magnetic Pickup: It's technically called aVR (variable reluctance sensor). It doesn't need magnetized teeth or an external power source, but the signal is AC (alternating current), and the output voltage also varies with the engine RPM, up to 50 volts or more! So you will need a much more complex circuit than the Hall Effect sensor. The VR sensor is cheaper but lager than the Hall Effect sensor.

author: Toble_Miner
author_rank: Contributor
timestamp: October 07, 2013, 01:46:22 am
content: Quote from: Dave on October 07, 2013, 01:08:17 amIt this is the only problem you could just encapsulate the section of the shaft the whole optical measurement stuff is on in a small plastic case. Also I think it's quite hard to block the entire light passing through a light barrier. The emitter- and receiver-area are both quite big in most light barriers.

author: hechen
author_rank: Newbie
timestamp: October 07, 2013, 01:46:34 am
content: What engine are you trying to install it on? Most modern engines have crank sensor with tone wheel and cam position sensor as well. You could calculator the rpm with either of these signals. I would not recommend installing your own tone wheel because it could "unbalance" the crankshaft.

author: deth502
author_rank: Frequent Contributor
timestamp: October 07, 2013, 01:53:06 am
content: most new engines have the fuel "distributor cap" electronically controlled, as opposed to the older engines that were mechanically controlled. (forgive my lack of knowledge on the correct terms. most of my work is done on gasoline engines, i rarely have to work on our diesel equipment). the diesel engine is run off of injections of fuel to each cylinder, much in the same way a gas engine is run by applying spark to the fuel in each cyl. this is analogous to your old distributer run off of your camshaft, while the newer ones are computer controlled through coil packs.but i digress. the newer electronically controlled engines derive the tach signal from the computer. i would look into possibly tapping into that some how.on an older mechanical engine, if it were me, id stray away from the flywheel and look to the balancer up front to get a signal from.

author: Icchan
author_rank: Regular Contributor
timestamp: October 07, 2013, 02:00:37 am
content: Somehow I personally would use optic measurement... since there's need for quite fast speeds and high reliability. Shine an infra red LED trough the teeth of a gear and use photo detector (diode) with IR filter to measure the pulses. feed the signal trough an amplifier to micro-controller or some ready made frequency counter and you're done. Even if the duty cycle isn't 50% it should be able to calculate the edges. I would think you could get more than enough performance from this

author: NDT
author_rank: Contributor
timestamp: October 07, 2013, 02:02:05 am
content: Quote from: deth502 on October 07, 2013, 01:53:06 amDiesel Engines have "heater" plugs, they are not for igniting the air/fuel mixture, just to get the engine started easier when it's cold. The air/fuel mixture is ignited because of the high temperature generated by the compression of the mixture inside the cylinder. So, diesel engines don't have a distributor, or spark plugs synchronized with the engine RPM neither in mechanical or electric or electronic form. They don't have coil packs either.Of course if it's a diesel engine with an ECU of some sort, it's really easy to tap into the RPM output line and get the RPMs from there.

author: Maximus64
author_rank: Newbie
timestamp: October 07, 2013, 02:03:56 am
content: How about read signal from the fuel injector? It can be used to calculate the RPM I think.

author: drake
author_rank: Newbie
timestamp: October 07, 2013, 02:05:29 am
content: I agree with everyone else, don't add any weight to the crank shaft/flywheel. I work at a shop where we balance flywheels for diesel trucks and its precision work. If the engine is older and doesn't have electronic sensors to tap into on either the crank or cam, maybe you can pick up a signal from the harmonic balancer.

author: NDT
author_rank: Contributor
timestamp: October 07, 2013, 02:07:04 am
content: Quote from: hechen on October 07, 2013, 01:46:34 amIf the trigger wheel is already balanced (as all commercial trigger wheels are) there's no problem fitting one.

author: deth502
author_rank: Frequent Contributor
timestamp: October 07, 2013, 02:07:09 am
content: Quote from: NDT on October 07, 2013, 02:02:05 amno, like i said, they have a fuel injector pump that work in that fashion. i made the distributor cap reference to describe how the fuel is metered in a diesel engine. im sorry if that was unclear.

author: hechen
author_rank: Newbie
timestamp: October 07, 2013, 02:09:07 am
content: Quote from: Maximus64 on October 07, 2013, 02:03:56 amThis method is not 100% accurate; when you let off the accelerator there will be a pause on the fuel injector.

author: NDT
author_rank: Contributor
timestamp: October 07, 2013, 02:11:36 am
content: One thing we all agree on: if we don't know what type of diesel engine we are talking, any solution could be adopted. If it has a mechanical fuel pump, or an electric one but with mechanically controlled injectors, the only way to go is a sensor in the crankshaft. Unless of course it has an ECU outputting an RPM signal.Please Gregory, would you be kind and clarify this point?

author: hechen
author_rank: Newbie
timestamp: October 07, 2013, 02:13:55 am
content: Quote from: NDT on October 07, 2013, 02:07:04 amIts the method of mounting the trigger wheel/ tone wheel that will cause unbalancing.

author: IanB
author_rank: Super Contributor
timestamp: October 07, 2013, 02:15:38 am
content: Quote from: NDT on October 07, 2013, 02:02:05 amBut diesel engines do have fuel injection, and they therefore have fuel injectors to inject fuel in a precisely controlled way at each cylinder. The fuel injection is absolutely synchronized with the engine RPM (how else would the engine run?) and in the case of electronic direct injection the injectors may look somewhat similar to a coil pack. I read nothing inaccurate in what deth502 wrote.

author: dacrawf
author_rank: Unknown
timestamp: October 07, 2013, 02:16:53 am
content: Modern electronically controlled diesel engines can have multiple pilot, a main, and multiple post injections per stroke for each cylinder. So measuring injection pulses is not a reliable way to go. The flywheel should have notches around its circumference that the OEM crank shaft sensor is using, check to see if the flywheel housing has places to mount additional VR or hall effect sensors. As pointed out, another option would be to measure the speed on the front side of the engine via the balancer or some other component that is part of the belt drive. If the engine electronics are equipped with a open communications bus such as SAE J1939, you could read the data from that... Best of luck...

author: Paul Moir
author_rank: Frequent Contributor
timestamp: October 07, 2013, 02:17:37 am
content: Left field idea; if looking for a generic way to fit to any (hopefully multicylinder) engine: a piezo electric sensor like a knock sensor. Required engine installation would be therefore a simple bolt.If going for a specific engine the magnetic pickup/gear method is very good. You get lots of pulses/rev off say the flywheel ring gear. Just use some some off-the-shelf automotive pickup that's magnetic. That said, tachometers work well enough off 2 signals/rev for example with 4 cylinder, 4 stroke spark ignition engines.

author: NDT
author_rank: Contributor
timestamp: October 07, 2013, 02:18:27 am
content: Quote from: hechen on October 07, 2013, 02:13:55 amAgain, if it's a commercial trigger wheel it mounts with the same hardware as the crankshaft pulley, so you are not adding/substracting off-balance weight

author: dacrawf
author_rank: Unknown
timestamp: October 07, 2013, 02:21:21 am
content: Quote from: IanB on October 07, 2013, 02:15:38 amThe problem is, you don't know how many injections are being done each stroke. Some diesel engines can do 5 or more injections per cylinder per compression/combustion stroke. This will very based on ambient conditions, engine load, engine operating mode, and many other things...

author: NDT
author_rank: Contributor
timestamp: October 07, 2013, 02:23:09 am
content: Quote from: IanB on October 07, 2013, 02:15:38 amAgain, MODERN diesel engines have EFI. But as I've said already, mechanical pumps or electric pumps with mechanically controlled injectors don't have the surrounding paraphernalia to extract a useful RPM signal of them. Anyway, until more is known about the engine used, we are all speculating.

author: deth502
author_rank: Frequent Contributor
timestamp: October 07, 2013, 02:28:34 am
content: Quote from: dacrawf on October 07, 2013, 02:21:21 amtrue, and the on-board computer derives the tach signals from these. which is what i recommended, trying to tap into the computers tach signal that it is already generating. i never recommended taking a pulse directly from an injector for this very reason.

author: hechen
author_rank: Newbie
timestamp: October 07, 2013, 02:39:38 am
content: This engine most likely has a electrical method of injecting fuel (no carburetor, etc). If this is the case there needs to be some kind of crank position input to the ECU (i.e. crank sensor). The easiest method is tapping into the crank sensor but I would not recommend it. I would recommend tapping into the CAN network and getting the RPM off of that.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: October 07, 2013, 02:45:02 am
content: Quote from: hechen on October 07, 2013, 02:39:38 amDiesels don't use carburetors, and most don't use an electrical way of injecting it. What we really need to know here is what kind of engine he's trying to measure the RPMS of. I'm picturing an old Westerbeke marine diesel. But maybe it's a car engine with a CAN bus and all sorts of goodies attached. Or perhaps it's a model airplane glowplug engine? I'm guessing it's not a locamotive or a Wärtsilä since those often come with tachometers already.Second left field idea: Does it have an alternator? What about measuring the current wave out from it?

author: IanB
author_rank: Super Contributor
timestamp: October 07, 2013, 02:52:59 am
content: Quote from: gregoryfenton on October 07, 2013, 12:27:17 amI'm rather interested in why this project is so good and why it makes Gregory so proud to be involved with it...?

author: peter.mitchell
author_rank: Super Contributor
timestamp: October 07, 2013, 03:46:25 am
content: I assume the engine is driving something, not just an engine, so it will probs have a water pump or powersteering pump, which may be driven directly from the engine, to which it may be more practical to measure the rpm from.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: October 07, 2013, 04:08:17 am
content: Quote from: IanB on October 07, 2013, 02:52:59 amFool me.... You can't get fooled again!Damn contests!

author: johnwa
author_rank: Frequent Contributor
timestamp: October 07, 2013, 05:33:26 am
content: Quote from: Paul Moir on October 07, 2013, 02:45:02 amYes, depending on the engine, this would probably be easiest. I recently had a similar need to monitor the speed of an approx. 4kW diesel powered water pump. I was looking at fitting a sensor to run off the cooling fan or the starter ring gear, but in the end I took a signal from the output of the alternator (which was fitted directly onto the crankshaft). No mechanical modifications needed! The alternator must have been a 6 pole design too, as the speed turned out to be a simple factor of ten times the output frequency.EDIT: I meant six pole, single phase - a three pole alternator would not make very much sense!

author: gregoryfenton
author_rank: Newbie
timestamp: October 07, 2013, 07:46:01 am
content: The engine would be a nautical one, it is for use on a small (43 feet) boat.I can't believe how much debate this question has startedI hope that narrowing down the engine type will help choose the correct option.Thanks again all for your comments thus far and any further commentary

author: G7PSK
author_rank: Super Contributor
timestamp: October 07, 2013, 07:56:03 am
content: The engine presumably has an electric start so there would have to be a starter ring gear, put a hall sensor close to that and count the teeth most ring gears will have enough residual magnetism to be seen by a hall sensor. Not my idea I have seen this commercially done.

author: fcb
author_rank: Super Contributor
timestamp: October 07, 2013, 08:36:09 am
content: Quote from: G7PSK on October 07, 2013, 07:56:03 am+1 for a hall effect looking at the ring-gear. Buy one off ebay "crank sensor" or "flywheel sensor" and use that.If you don't want to get *that* involved, then you could always use a small microphone and listen to the exhaust. I don't think you'll need much in the way of signal processing to create a pulse per detonation.

author: NDT
author_rank: Contributor
timestamp: October 07, 2013, 08:53:00 am
content: Quote from: gregoryfenton on October 07, 2013, 07:46:01 amBesides it being for a boat, could you tell something more about it? The most important thing, does it have EFI (electronic fuel injection) or the fuel injection system is of the mechanical type?

author: NDT
author_rank: Contributor
timestamp: October 07, 2013, 09:01:28 am
content: Quote from: johnwa on October 07, 2013, 05:33:26 amIn applications where the engine drives loads at constant speeds (i.e. alternators as emergency generators, hydraulic pumps, etc) or if the accessory being driven, as is your case, has a direct or rigid mechanical connection with the engine, it's perfectly fine to do as you tell. On most engines, including marine engines, the accessories are driven by a pulley and belt system and the belt slippage plays ebb important role on the dependability of the RPM indication. If the engine is used in such a way that its power output is rapidly changing, or if the belt has wear, or if the tension isn't adequate, belt slippage could be significant.

author: gregoryfenton
author_rank: Newbie
timestamp: October 07, 2013, 09:15:43 am
content: Quote from: Paul Moir on October 07, 2013, 04:08:17 amThe timing is rather iffy with the contest and all I appreciate (not trying to bump my post count), but this is a genuine thread.I am not at liberty currently to reveal the nature of the project but when it is revealed you will understand my pride, you may even have pangs of "I am so envious, what a great thing to be involved in."I will see if Dave will comment and inform you of my genuine intentions. @eevblog message incoming!

author: EEVblog
author_rank: Unknown
timestamp: October 07, 2013, 09:45:52 am
content: Quote from: gregoryfenton on October 07, 2013, 09:15:43 amYep, confirmed. It's a real project.

author: gregoryfenton
author_rank: Newbie
timestamp: October 07, 2013, 09:50:12 am
content: Quote from: EEVblog on October 07, 2013, 09:45:52 amYour reply is very much appreciated Dave

author: mjrandle
author_rank: Contributor
timestamp: October 07, 2013, 10:33:19 am
content: Not sure what sort of accuracy you requie, but if the diesel engine has an alternator then it probably has a tacho output on the alternator. Given the crank and alternator pulley effective diameter you would then be able to calculate engine speed.Cheers,Mike

author: johnwa
author_rank: Frequent Contributor
timestamp: October 07, 2013, 11:16:23 am
content: Quote from: NDT on October 07, 2013, 09:01:28 amYes, I agree, if there is a belt involved, this is probably not the best method. Although a properly designed belt drive in good condition should not have much slip, there are too many variables for this to give an absolute indication of speed.

author: Lifeboat_Jim
author_rank: Contributor
timestamp: October 07, 2013, 11:49:31 am
content: Hi GuysI'm Gregs partner in crime in this project. Firstly a massive thank you for the interest shown in helping out with advice & suggestions, very much appreciated!Many of you have asked for details, so Greg gave me a nudge to register here and provide them directly.Background and detailsAs mentioned previously, it's a boat (in a couple of weeks time we'll unveil all the details) project but this is an ancillary aspect to it.The engine in question is single cylinder diesel, direct injection, mechanical governor (for those diesel heads it's a 1995 Lister PetterAD1C, Build 02... so Ring Gear with the optional electric starter and variable speed 1,000-3,600RPM circa 7.5HP @ 3,600RPM). Currently hooked up to an Ingersoll Rand 'Euro' Air Compressor Pump Head via belts. It has absolutely no modern features, no alternator, no electronics etc. It doesn't have a Heater Plug (this is an option, but not fitted). This is the sort of engine used on Concrete Mixers, temporary Traffic Lights, Compactors, Water Pumps etc.This was bought to drive a Shot Blaster for the boat restoration aspect. Once that phase is done I was minded to take the Compressor Pump off and fit a GenSet (or possibly a heavy duty 24v Alternator) and fit it on the boat as a power source (battery charging etc) thereby squeezing every last drop of value out of itThe ultimate plan is to; measure the RPM, fit a Relay to the Starter circuit, add Servos to operate the Decompressor and Engine Stop. In short have the ARM based microcontroller automate/monitor it, but of course each of those one step at a time.This small standalone simple engine becomes the proof of concept/test bed for...Big Marine EngineWell, this is for a several months time but the main propulsion engine is a 1964 Parsons Porbeagle (a marinised Ford(son) 4D, 4 cylinder Diesel) yielding 57HP @ 2,250 RPM iirc. Again, as you may imagine from the vintage, lacking all the mod-cons). The boat has/had two of these directly attached to each of the two prop-shafts.We're looking hard into switching from two of these directly coupled to just the one. This will then drive a Hydraulic Pump and the props will be, in turn, driven from individually controlled Hydraulic Motors.End goalsTo remotely monitor all aspects of both the small and large engines (RPM, Start/Stop, Fuel, Oil, Temperature etc) and remote control them.Also to measure the direction and speed of the two prop-shafts.RPMSo, back to the original task/question 'How would i measure RPMs in a diesel engine?'.Thoughts about usingTCRT5000L Reflective Optical Sensor with Transistor Output(and a Schmitt Trigger to smooth the output)? I see many fans of Hall Effect (and some very good reasons why being put up too). Given measuring the prop-shafts is also a consideration and standardising on a single method has advantages the IR route is certainly attractive, and IR has its supporters here too. Perhaps we need both, Hall Effect on the Engines and IR on the prop-shafts?CheersJim.

author: jeroen74
author_rank: Frequent Contributor
timestamp: October 07, 2013, 01:42:53 pm
content: One method is to mount a small (piezoelectric) microphone to one of the injector pipes. The high pressure pulse is easy to detect; easily even by ear if you use a stethoscope or the screwdriver method.

author: Lifeboat_Jim
author_rank: Contributor
timestamp: October 07, 2013, 01:49:48 pm
content: Quote from: jeroen74 on October 07, 2013, 01:42:53 pmInteresting. you're the 2nd to mention acoustic measurement. When mounted on the boat they'll exhaust through silencers (interesting factoid... 'hospital(ler) silencers' are thought to derive their name by being quite enough to be used in/near Hospitals... sounds sensible enough to be true!). With two diesels running in the same compartment I wonder how effective/accurate it would be to implement. Perhaps going for vibration rather than sound waves?They do that in F1 by the way to spy on other peoples cars (as they have detailed telemetry on their own of course).Anyway, that is a possibility for engine RPM (assuming the difficulties, aren't), but an interesting project nevertheless perhaps as a redundancy method, but not for prop-shaft revolutions so we'd still need a solution for that.

author: NDT
author_rank: Contributor
timestamp: October 07, 2013, 02:09:03 pm
content: I still think that you should go with the hall effect sensor. And since you plan on monitoring other engine parameters, you also should go with the corresponding automotive sensors according with what you want to measure. The sensors that you need (hall effect for the crankshaft and propeller, temp sensor in the form of an NTC or PTC sensor for air, fuel, or other fluid, etc) are already available and specifically designed for engines, so, why reinvent the wheel? They are rugged, dependable, accurate, and cheap to not too expensive.

author: Mr Smiley
author_rank: Frequent Contributor
timestamp: October 07, 2013, 02:09:53 pm
content: Do Diesel engines "Knock" like over lean / low grade fuel petrol engines

author: Lifeboat_Jim
author_rank: Contributor
timestamp: October 07, 2013, 02:14:33 pm
content: Quote from: NDT on October 07, 2013, 02:09:03 pmCould you expand on that please? NTC/PTC etc. I'm a complete n00b on electronics. Although Greg is quite handy on general electronics I don't think he'd know what those are either.

author: Rigby
author_rank: Super Contributor
timestamp: October 07, 2013, 02:33:58 pm
content: J1939 is how I would do it. If the engine is even close to modern and it goes in a vehicle then it has a data bus. CAN, MODBUS, ISOBUS, something. The tach measurement will probably already be in there. There are small pump-house diesels that don't have a databus, though, and if this is the case with you, then I would find a good spot to paint a white mark and observe it digital laser tachometer or something.

author: jeroen74
author_rank: Frequent Contributor
timestamp: October 07, 2013, 02:41:05 pm
content: It's a simple one cilinder diesel... not automotive at all. No fancy ECUs and databusses.Looks like thisI guess?

author: Lifeboat_Jim
author_rank: Contributor
timestamp: October 07, 2013, 02:48:31 pm
content: Yes, scroll up to my detailed post. I also linked to the actual Lister Petter AD1 engine.

author: NDT
author_rank: Contributor
timestamp: October 07, 2013, 03:29:31 pm
content: Quote from: Lifeboat_Jim on October 07, 2013, 02:14:33 pmOf course... actually, it's very simple. NTC and PTC refer to Negative Temperature Coefficient and Positive Temperature Coefficient. These sensors are just resistive elements whose value changes with temperature. In a NTC, the resistance of the sensor decreases as the temperature increases; in a PTC you have the opposite case, as the temperature increases the resistance of the sensor increases also. In the automotive word these type of sensors, regardless of the temperature coefficient, come in two basic "flavours": CLT, which means coolant temperature sensor, for measuring the liquid coolant temperature, and MAT, or manifold air temperature, for measuring the temperature of the air entering the engine. The difference lays on the type of exposure protection of the sending element. There are also fuel temperature sensors, they are similar to CLTs, but I've never used them so I can't express an informed opinion. I think you should make a list of all the parameters that you want to measure and from then see which sensor you'll be using for what.One other thing I forgot to mention: if you want to control the starting of the engine with the microprocessor, it's essential that you use a sensor system that gives you a lot of pulses per revolution, in order to stop the current flow to the starter in the right moment.

author: arvidj
author_rank: Contributor
timestamp: October 07, 2013, 04:13:00 pm
content: When I was looking for a tachometer for three cylinder Yanmar Diesel in my tractor I found these:This group decided that a sensor on the injector fuel line was a reasonable way to solve the problem:http://tinytach.com/new_features_diesel.phpAutometer like the "alternator" approach:http://www.autometer.com/productPDF/608.pdf,as did this group ...http://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=128/prd128.htmThis fellow thought an optical sensor was a good idea ...http://www.4crawler.com/Diesel/CheapTricks/Tachometer/index.shtmlI also looked at one of the many devices that would sense the teeth on the ring gear.In the end I decided that most of the implements I use on the tractor require that I run it WFO so a tach would not be of great value. But the research did show that "the problem already has several reasonable solutions", one of which might be applicable to your situation.

author: G7PSK
author_rank: Super Contributor
timestamp: October 07, 2013, 05:34:48 pm
content: Its a Petter then. I have rebuilt many of those in my life. The injector pump is a CAV bosch type two things come to mind one the injector pipe has a distinctive pulse so a strain gauge on that might work or a piezo. the other is inside the pump under a small cover is an adjustment screw this goes up and down with the plunger it would be possible to arrange for a contact to touch this at some point.

author: G7PSK
author_rank: Super Contributor
timestamp: October 07, 2013, 08:41:40 pm
content: I dont have the service book for the AD1 but do have it for the AA1-AB1 this is the smaller brother of the AC1-AD1 they also made an AC2-AD2 twin cylinder which was very popular for mobile welders at one time.Any way I have had a look at the book and a number of thoughts arise the best option is probably to use a sensor (hall) on one of the extension shafts, I don't know how the drive is taken on your engine but there was three options flywheel either direct or with a shaft extension a crankshaft extension on the other end an a half speed shaft as an extension of the camshaft this shaft is transposable from crank to cam just swap the covers over or you can have two shafts.There is another way you could use a valve rocker. There is also a number of holes drilled into the flywheel for balancing purposes which might also be used with a hall sensor.What you don't want to do is disturb the pump timing as they are a pig to time, it has to be don by finding the spill postion and adjustment is made by adding or removing shims under the pump, I have had to do this in the past and to get it dead right can take half a day, most people don't go this far but done right these engines will run like sewing machine.

author: fcb
author_rank: Super Contributor
timestamp: October 09, 2013, 01:17:24 pm
content: Why make life difficult? If you have a ring-gear, then just fit an standard crank angle sensor from a car, they're a tenner (new) from ebay etc.. and someone else has made them oil/dust/waterproof and neatly connectorised it for you...

author: Anks
author_rank: Frequent Contributor
timestamp: October 09, 2013, 11:15:59 pm
content: Thinking outside the box you could always use the waveform generated by the alternator if it has one. Just tap it before one of the diodes. Also depending on how the charging system is designed you could a current meter to see this.

author: Lifeboat_Jim
author_rank: Contributor
timestamp: October 10, 2013, 01:48:40 pm
content: Ladies & Gents, Boys & Girls...Many thanks for all the suggestions.Alas the Lister Petter AD1 engine is being very naughty and not playing ball (low compression), and I've run out of time and talent. My mechanical knowledge is as poor as my electronics obviously, and now it's down to stripping down and regrinding valves/pistons etc.I bought it with an Air Compressor head attached to drive a Shot Blaster so it was a means to an end. I then thought to take off the Compressor and put a GenSet on and continue to use it (possibly switching the Compressor head back in for occasional future use).I will persevere with it but with winter coming and time against us its time to just hire in a Compressor and crack on with the main project so this aspect will have to be parked for a few months :-(Having said that, the thought process of 'measuring RPMs' in a simple diesel engine was valuable and directly transferable to the main marine engine. Plus I have hopes in the future for the little AD1 (if not this one, another) with more time, effort and a little cash.For the AD1 it looks like the teeth of the Gear Ring is the way forward (or the flywheel, which has one cut out on its outer edge), not all AD1 have Gear Rings but at least this one does.Many thanks for all the help/assistance. Special shout out to G7PSK who has gone the extra mile with much advice via e-mail/PM.No doubt Greg and myself will be back to pick your collective brains with regard to other aspects of this project in due course. I know there has been some flaming of attitudes in this 'Beginners' Forum but you've been fantastic to Greg & myself... which is nice ;-)o7@ Anks... no alternator@FCB... Agreed. Didn't know what they were called nor the pro's/con's compared to other methods.

author: Anks
author_rank: Frequent Contributor
timestamp: November 21, 2013, 04:20:26 am
content: Quote from: Lifeboat_Jim on October 10, 2013, 01:48:40 pmJust noticed what sort of engine it is sorry. I would go with an hall sensor on the crank simple and effective.

author: Lifeboat_Jim
author_rank: Contributor
timestamp: November 21, 2013, 09:54:55 am
content: Yep.Hall Effect was always my favourite option. However we'd never thought of a Crank Angle Sensor (aka Crank Position). The flywheel does have teeth of course.Much time has passed in getting the bloody engine working and in tip top condition. That's done now.Yesterday the Postie brought one of those cheap Laser Tachos, and I'm looking at what ebay has to offer for a Crank Sensor... need a small diameter to fit, ideally 12.5mm/ half inch. Motorcycle sensor perhaps.

author: trackman44
author_rank: Regular Contributor
timestamp: November 21, 2013, 01:30:55 pm
content: I would use the crank timing wheel from a Ford Escort engine and it's sensor, very reliable and no worries about dirt contaminating an opto sensor arrangement. If you can get to a scrap yard and get the timing wheel and sensor (the timing wheel has 35 teeth plus one missing tooth) you could measure for the missing tooth ( it is an ac signal with a train of 35 cycles and one missing).This arrangement is used in an electronic ignition system called MegaSpark (It's part of the MegaSquirt DIY fuel injection system), here's a link :-http://home.comcast.net/~tjhafner/SparkManual.htmlGood luck with the project.Will