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| Thread ID: 38925 | 2003-10-22 04:55:00 | Off Topic | B.M. (505) | Press F1 |
| Post ID | Timestamp | Content | User | ||
| 185640 | 2003-10-22 04:55:00 | Here’s one for all you bright sparks. I’ve been coerced into replacing the tachometer in a mates boat. (Electrolysis and salt water killed the old one) Now the motor is a 4 cylinder high speed Volvo Penta diesel. I’ve purchased (at huge cost) a new all-purpose Datcon tachometer, which will work fine off the alternator. The problem being calibrating it after installation. It has a switch / potentiometer combination for calibration. Ok, what I want to do is manufacture (out of cardboard or similar) a round disk with equal black and white segments which I can stick to the motors front pulley and will show as being stationary when strobed with a mains driven (50 hz) florescent lamp. So, the question is, how many segments would I have to divide my disk into for it to show as being stationary with the motor spinning at say 1000 rpm? I think the problem is not getting harmonics where the disk shows as stationary at a number of revolutions in close proximity to what you want. I can remember making these disks for adjusting machinery shaft speeds some 40 years ago but cant remember the formula. Cheers Bob |
B.M. (505) | ||
| 185641 | 2003-10-22 08:29:00 | I get 3 with my very poor math. But wouldn't it still only strobe at 50rps which I make at 3000rpm. Cheers Murray P |
Murray P (44) | ||
| 185642 | 2003-10-22 20:16:00 | Thanks Murray 3's a number I hadn't come up with, but then my maths are awful rusty. |
B.M. (505) | ||
| 185643 | 2003-10-23 03:35:00 | Of course the fluorescent will flicker at 100Hz. :D This thing has a knob for calibration? There's only a few different numbers of poles used for alternators. The number of cylinders doesn't come into it, when you are using the alternator AC sample. |
Graham L (2) | ||
| 185644 | 2003-10-23 04:03:00 | I've used google to refressh my memory: If you have one line on the disk the "frequency" (f )it gives is 1X the revs/sec . More (equally spaced) lines gives multiples of that frequencyu . If the strobe light's frequency is f1, the line will appear stationary when i\f = nf1 . At 3000 rpm (50 rps) a 2 line disk would appear stationary when illuminated by a 100 Hz flicker . So 6 lines would be OK for 1000 rpm . |
Graham L (2) | ||
| 185645 | 2003-10-23 08:33:00 | Good one Graham . Jeez it’s a bugger when old timers disease and CRAFT disease hits you . :( Your quite right, we’re looking at 100hz flicker . Stupid oversight, like the hum we sometimes got in old Valve radios . Usually referred to as 50hz hum when in fact it was 100hz . I thought of looking on google but couldn’t work out how to word the question . :D Again you’re right about the alternator . Anyway, that’s my project for the weekend so I’ll let you know . |
B.M. (505) | ||
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