Tachometer

[Jerry Hammernik]

The tachometer on Lion's Paw quit working last year and after discussing it on this board I was unwilling to pay the kind of prices that members had been getting. I've now located a VDO tach that according to the dealer (he checked with VDO) should work for my application. And it was only $142 including an hourmeter. (Only?)

Now here's my question. To calibrate it I need to know the number of pulses per rpm of the engine. (My Volvo MD7B has an inductive sending unit.) It would be a number like 16.5 pulses per revolution of the engine. Anybody know what this number is for this engine. Thanks for any help.

Jerry Hammernik
Lion's Paw CD28 #341



dauntles@execpc.com

[marv]

The tachometer on Lion's Paw quit working last year and after discussing it on this board I was unwilling to pay the kind of prices that members had been getting. I've now located a VDO tach that according to the dealer (he checked with VDO) should work for my application. And it was only $142 including an hourmeter. (Only?)

Now here's my question. To calibrate it I need to know the number of pulses per rpm of the engine. (My Volvo MD7B has an inductive sending unit.) It would be a number like 16.5 pulses per revolution of the engine. Anybody know what this number is for this engine. Thanks for any help.

Jerry Hammernik
Lion's Paw CD28 #341

Compute the radius of the shaft diameter and divide by its parabolic equivalnet. ad this to the water line length plus the specific gravity of plutonium 308 and you will come up with some type of number that has nothig at all to do lwith anything



mibrinn@aol.com

[John R.]

The tachometer on Lion's Paw quit working last year and after discussing it on this board I was unwilling to pay the kind of prices that members had been getting. I've now located a VDO tach that according to the dealer (he checked with VDO) should work for my application. And it was only $142 including an hourmeter. (Only?)

Now here's my question. To calibrate it I need to know the number of pulses per rpm of the engine. (My Volvo MD7B has an inductive sending unit.) It would be a number like 16.5 pulses per revolution of the engine. Anybody know what this number is for this engine. Thanks for any help.

Jerry Hammernik
Lion's Paw CD28 #341

Yes you do need the pulse signal rate, I believe I have it somewhere and will check all my files for it. I will post it asap if I can find it. I have it from several years ago when I retro fitted an adjustable Teleflex tach in someone else's CD. I would certainly call Volvo, that is a spec they would still have on file.

[Jerry Hammernik]

We'll I tried to contact Volvo to get the pulse per rpm number. They spent some time looking and finally offered to sell me a new tach for $300. Their best suggestion was to count the teeth on the gear (probably the cam gear) that the sending unit is reading. I explained to them that I would need to pull the engine to do that!

So my best hope at this point is that John R. can locate the number. The fall back plan is to take my best guess until I can get better answers. Ever notice why everyone that repowers chooses Yanmar instead of Volvo!

Jerry Hammernik
Lion's Paw CD28 #341

The tachometer on Lion's Paw quit working last year and after discussing it on this board I was unwilling to pay the kind of prices that members had been getting. I've now located a VDO tach that according to the dealer (he checked with VDO) should work for my application. And it was only $142 including an hourmeter. (Only?)

Now here's my question. To calibrate it I need to know the number of pulses per rpm of the engine. (My Volvo MD7B has an inductive sending unit.) It would be a number like 16.5 pulses per revolution of the engine. Anybody know what this number is for this engine. Thanks for any help.

Jerry Hammernik
Lion's Paw CD28 #341

dauntles@execpc.com

[John R.]

We'll I tried to contact Volvo to get the pulse per rpm number. They spent some time looking and finally offered to sell me a new tach for $300. Their best suggestion was to count the teeth on the gear (probably the cam gear) that the sending unit is reading. I explained to them that I would need to pull the engine to do that!

So my best hope at this point is that John R. can locate the number. The fall back plan is to take my best guess until I can get better answers. Ever notice why everyone that repowers chooses Yanmar instead of Volvo!

Jerry Hammernik
Lion's Paw CD28 #341

The tachometer on Lion's Paw quit working last year and after discussing it on this board I was unwilling to pay the kind of prices that members had been getting. I've now located a VDO tach that according to the dealer (he checked with VDO) should work for my application. And it was only $142 including an hourmeter. (Only?)

Now here's my question. To calibrate it I need to know the number of pulses per rpm of the engine. (My Volvo MD7B has an inductive sending unit.) It would be a number like 16.5 pulses per revolution of the engine. Anybody know what this number is for this engine. Thanks for any help.

Jerry Hammernik
Lion's Paw CD28 #341

Jerry,
I'm still searching for it as I have time. Volvo should have connected you with someone in engineering and they could have looked it up. I'll check some more places tonight also.

[John MacArthur]

snip

Now here's my question. To calibrate it I need to know the number of pulses per rpm of the engine.

A friend with some other kind of motor had the same problem, and solved it by using an old-style machinists mechanical revolution counter to actually count the RPM of the motor. By comparing this with the read-out RPM, he was able to calibrate it. These rev counters are still available in some tool catalogs, and probably in many junk tool stores. You just hold it to the center-pip in the middle of the flywheel (probably much easier said than done in a CD), and read out the number of revolutions made in one minute.



jmac@laplaza.org

[Larry DeMers]

I suspect that it is one pulse per revolution, but it depends on the pick-up point too. Most engines take a pulse off of their alternator, so the tachometer has to be bought or programmed to accept the number of poles that their alternator has (14 or16 poles etc.). Our MD7B pickup is magnetic, but where is the pickup at?

The magnetic sensor is really a magnet and microswitch or Hall Effect Device combination, which closes whenever the magnetic field becomes strong enough as the rotating part goes by. It would be perfectly fine to use a single magnetic contact to derive the rpm of the engine, and I would be surprised if they provided more than a single magnet for this operation. So where would they get a number like 16.5 from? A half of a pulse? no, something is confused here me thinks. Sure they were not talking about an alternator sourced signal needing to be calibrated to the number of poles in the alternator? That would be a number like 12 or 16 (not a frational number however)

If I have time this next weekend, I can put my frequency counter on the tach wires and see what is being presented to the Tach.

Larry DeMers
s/v DeLaMer
Cape Dory 30

We'll I tried to contact Volvo to get the pulse per rpm number. They spent some time looking and finally offered to sell me a new tach for $300. Their best suggestion was to count the teeth on the gear (probably the cam gear) that the sending unit is reading. I explained to them that I would need to pull the engine to do that!

So my best hope at this point is that John R. can locate the number. The fall back plan is to take my best guess until I can get better answers. Ever notice why everyone that repowers chooses Yanmar instead of Volvo!

Jerry Hammernik
Lion's Paw CD28 #341

The tachometer on Lion's Paw quit working last year and after discussing it on this board I was unwilling to pay the kind of prices that members had been getting. I've now located a VDO tach that according to the dealer (he checked with VDO) should work for my application. And it was only $142 including an hourmeter. (Only?)

Now here's my question. To calibrate it I need to know the number of pulses per rpm of the engine. (My Volvo MD7B has an inductive sending unit.) It would be a number like 16.5 pulses per revolution of the engine. Anybody know what this number is for this engine. Thanks for any help.

Jerry Hammernik
Lion's Paw CD28 #341

Jerry,
I'm still searching for it as I have time. Volvo should have connected you with someone in engineering and they could have looked it up. I'll check some more places tonight also.

demers@sgi.com

[John R.]

I suspect that it is one pulse per revolution, but it depends on the pick-up point too. Most engines take a pulse off of their alternator, so the tachometer has to be bought or programmed to accept the number of poles that their alternator has (14 or16 poles etc.). Our MD7B pickup is magnetic, but where is the pickup at?

The magnetic sensor is really a magnet and microswitch or Hall Effect Device combination, which closes whenever the magnetic field becomes strong enough as the rotating part goes by. It would be perfectly fine to use a single magnetic contact to derive the rpm of the engine, and I would be surprised if they provided more than a single magnet for this operation. So where would they get a number like 16.5 from? A half of a pulse? no, something is confused here me thinks. Sure they were not talking about an alternator sourced signal needing to be calibrated to the number of poles in the alternator? That would be a number like 12 or 16 (not a frational number however)

If I have time this next weekend, I can put my frequency counter on the tach wires and see what is being presented to the Tach.

Larry DeMers
s/v DeLaMer
Cape Dory 30

I haven't found my notes yet but I think it may have been 12 Larry. Post what you find with the counter.

We'll I tried to contact Volvo to get the pulse per rpm number. They spent some time looking and finally offered to sell me a new tach for $300. Their best suggestion was to count the teeth on the gear (probably the cam gear) that the sending unit is reading. I explained to them that I would need to pull the engine to do that!

So my best hope at this point is that John R. can locate the number. The fall back plan is to take my best guess until I can get better answers. Ever notice why everyone that repowers chooses Yanmar instead of Volvo!

Jerry Hammernik
Lion's Paw CD28 #341

Jerry,
I'm still searching for it as I have time. Volvo should have connected you with someone in engineering and they could have looked it up. I'll check some more places tonight also.

[Olli Wendelin]

Jerry

You can calibrate your electronic tach by using a mechanical tach which you touch to the end of the shaft and it reads out in RPM.

Another method is to use a strobotach. This is a strobe light with a variable frequency. You adjust the tuning knob on the strobotach and view a rotating chalk mark on your shaft or pully just like an automotive timing light. When the chalk mark stops you read the RPM off the adjustment knob.

Another method involves approximation. You know the approximate top RPM and idle RPM of your engine. While tied to the dock check your tach reading at these two setting. Then vary pulse adjustment (14, 15, 16, 17 ?) until you get readings that agree with your two known RPM settings. This shouldn't be too hard.


Olli Wendelin
BLUE MOON
Charleston, SC



wendelin@spawar.navy.mil