Tachometers?

[NickC]

I'm curious as to what setups you guys are using for tachometers. I'm kind of confused on the whole subject. I know you need an optical sensor, not sure how to make one, and you have to attach it to a panel meter, which I'm not sure how to calibrate.

[tufty]

As well as the optical pickup, which is reasonably well documented on the web, google for "optical tachometer circuit", you'll also need something to convert pulses to readings. A good digital multimeter might be able to do this, or you could use something like an LM2907/2917 frequency / voltage converter (in fact, the application sheet for these is rather edifying and contains a number of ready-made circuits). For the sort of speeds we're talking about with turbines, you'll almost certainly need a step down between the pulse generator, this can be done relatively easily with a 74x74 (halving frequency, dividing by 4, dividing by 8, etc). There are dedicated frequency divider ICs that would allow you to divide by an arbitrary amount (for example, by 12 to get a half-rpm reading off a hex nut) but they are more expensive than the venerable 7474, and with a little ingenuity one can do much the same with a few 7474s.

Of course, you can combine the methods. pickup -> frequency divider -> multimeter, etc.

Simon

[NickC]

where do you buy that stuff?

[tufty]

where do you buy that stuff?

Any half-way-decent electronic supplier should be able to order whatever you want. Specific chips like the 2917 tend to be a bit pricey (not terribly; in bulk they are less than $1.00 each, but you have to buy thousands to get that price so suppliers will sting you 3 to 5 times that) but a good hint is to go the the manufacturers and ask for samples (they will often send you them free).

As an example, go to the national semiconductors site and find the page for the 2917 where you can request samples (you'll probably be interested in the MDIP package as opposed to the surface mount version)

As for stuff like the 74 series chips, well, I have a huge box full that have been "recovered" from dead equipment (somewhat brutally in some cases; see a dead VCR by the side of the road, rip out the pcbs, place upside down under the grill on standoffs until the solder gets soft and then tap the board with a wooden spoon)

Simon

[Fricke]

I'm curious as to what setups you guys are using for tachometers. I'm kind of confused on the whole subject. I know you need an optical sensor, not sure how to make one, and you have to attach it to a panel meter, which I'm not sure how to calibrate.

The easiest way to do it is to get a panelmeter that is ready made for mesuring RPM (about €100) and a optical fiber sensor (about €260) and then connect some wires and do some programming of the panelmeter and you have a fool proof tachometer that will read up to 420k RPM.

The fun way is to get the parts in the circuit attached and go the DIY route.
The parts shouldn´t cost more than about €50 including the tachometer.

[tufty]

The fun way is to get the parts in the circuit attached and go the DIY route.
The parts shouldn´t cost more than about €50 including the tachometer.

Oooh, that's nice.

I'd forgotten about 4017s, probably because I don't seem to have any in my bits box.

Simon

[Gripen]

or u can just by a optical rev counter and move the diod from the instrument to the intake

costs less than 50 euro here in sweden

[Fricke]

or u can just by a optical rev counter and move the diod from the instrument to the intake

costs less than 50 euro here in sweden

The ones I´ve seen only counts up to 99,999 RPM...

Another way to do it is to only take the "sensor" parts from the circuit above and connect the output to a multimeter that can measure freq. And either read direct from the hex-nut on the shaft and get the RPM/10.

[Gripen]

or u can just by a optical rev counter and move the diod from the instrument to the intake

costs less than 50 euro here in sweden

The ones I´ve seen only counts up to 99,999 RPM...

Another way to do it is to only take the "sensor" parts from the circuit above and connect the output to a multimeter that can measure freq. And either read direct from the hex-nut on the shaft and get the RPM/10.

okay maybe u are right...havent tested mine yet, but i think it goes higher

[NickC]

I'm curious as to what setups you guys are using for tachometers. I'm kind of confused on the whole subject. I know you need an optical sensor, not sure how to make one, and you have to attach it to a panel meter, which I'm not sure how to calibrate.

The easiest way to do it is to get a panelmeter that is ready made for mesuring RPM (about €100) and a optical fiber sensor (about €260) and then connect some wires and do some programming of the panelmeter and you have a fool proof tachometer that will read up to 420k RPM.

The fun way is to get the parts in the circuit attached and go the DIY route.
The parts shouldn´t cost more than about €50 including the tachometer.

In your diagram what is T1? I assume the pot is to adjust it? but how?

[Fricke]

In your diagram what is T1? I assume the pot is to adjust it? but how?

T1 is an Transistor NPN type any standard type works. It´s function is to emulate the breaker points for the tachometer input.

[NickC]

so when do you adjust the pot? I can't find and CD4017BC chips they're discontinued or something. where can I find them, like inside some kind of consumer electronic.

[Fricke]

so when do you adjust the pot? I can't find and CD4017BC chips they're discontinued or something. where can I find them, like inside some kind of consumer electronic.

The pot is part of the comparator circuit. You adjust the pot to get the best signal ratio, ideally the signal should have 50% on and 50% off...

the 4017 is still in production. seach on CMOS and 4017 on any major electronic supplier.

[NickC]

and for the infrared emitter and detector does it really matter what kind they are or just any emitter and detector? I think radioshack sells them and I can't find those exact part numbers

[Fricke]

and for the infrared emitter and detector does it really matter what kind they are or just any emitter and detector? I think radioshack sells them and I can't find those exact part numbers

I´m using these IR-LED and IR-phototransistors from Fairchild; QEC113 & QSC112 they are matched and only 3 mm in diameter.

But any one will do as long as the current thru them is not greater than the datasheet says.. It´s R1 and R2 that sets the current...