Tuning Forks? - Page 1
Forum section: electronics / testgear

author: IdahoMan
author_rank: Regular Contributor
timestamp: April 14, 2017, 01:23:25 am
content: Anybody use them?What kinds are there? What do you use/recommend?

author: AG6QR
author_rank: Frequent Contributor
timestamp: April 14, 2017, 04:09:16 am
content: I have a few of the type in your third picture (where you have three forks on wood, with two basic designs -- I own some of each) which I use for tuning my guitars. They're all at 440Hz, an "A" on the musical scale.For the purpose of tuning a guitar, they're excellent: simple, inexpensive, plenty accurate enough and stable enough, no batteries required, not much to go wrong. There's something satisfying about using a simple mechanical tuning fork to tune an acoustic guitar, with no electronics involved in either device.These days, for electronics purposes, quartz crystals provide a better value than metal tuning forks for most any purpose I can think of. But your posting prompted me to do some google searching, and it looks like there were niches where tuning forks were the best value in the past. I was aware of the Bulova Accutron watch my dad used to wear, and I remember listening to its tuning fork. But I wasn't aware of other uses in electronics. Here's one document I found.http://www.ase-museoedelpro.org/Museo_Edelpro/Catalogo/Overview/Tuning%20fork%20oscillators.pdf

author: edpalmer42
author_rank: Super Contributor
timestamp: April 14, 2017, 05:06:56 am
content: I have a cousin to the first one.The unit pictured is a General Radio oscillator that uses one (?) vacuum tube to amplify the signal. Mine is a General Radio 813-A and doesn't use any active devices whatsoever and still works as a 1000 Hz - oops - Cycle oscillator. Dates from the 1930's and not only still meets its original accuracy of 0.5%, it's actually less than 0.1% off!I hope I'm that sharp when I'm over 80 years old!Ed

author: gslick
author_rank: Frequent Contributor
timestamp: April 14, 2017, 05:32:14 am
content: RE: Bulova AccutronEEVblog #920 - World's First Transistor Watch!

author: ivaylo
author_rank: Frequent Contributor
timestamp: April 14, 2017, 06:25:46 am
content: They used to be used to tune teletypes and tlegraph typewriters' motors. If the motors of the machines on both ends of the wire (or radio connection) got out of sync you got gibberish. Those motors could be tuned in a kinda wide range. Remember them fondly in the end of 80s still being used by the Soviet bloc military. Not finding many references, but here is one for salehttp://www.ebay.com/itm/1-TUNING-FORK-180-Hz-VPS-Mil-Teletype-NSN-5815-00-224-9717-NOS-/141411259652

author: ebastler
author_rank: Super Contributor
timestamp: April 14, 2017, 07:10:18 am
content: Quote from: ivaylo on April 14, 2017, 06:25:46 amYes, I have one of those to adjust the motor speed of my trusty Lo-15 teletype. (A metric version of the Teletype Model 15; bought in 1980 as my first computer printer, when radio amateurs were happy to replace those noisy monsters by microprocessors for their RTTY transmissions...) Teletypes did come with mains-synchronous AC motors, but also with "all current" motors, which had to be adjusted to the correct speed to keep the serial data stream in sync with other stations.The two overlapping paddles at the tip of the tuning fork each have a slit, such that the slits line up twice per oscillation period of the fork. You see through those and observe white/black markers on the circumference of the motor's rotor. A centrifugal governor on the motor is adjusted to set the motor to the correct speed, at which the markers appear stationary. I can take photos of the motor and tuning fork if there's an interest.Off-topic here? Well, I guess the tuning fork does qualify as "test equipment".

author: voltsandjolts
author_rank: Unknown
timestamp: April 14, 2017, 07:22:35 am
content: They are interesting because they make an old electronics engineer learn a little more about physicsThey can be used for fluid density measurement with the advantage of being safer than radioactive measurements.http://www.emerson.com/catalog/en-us/micro-motion-density-fdm

author: georgd
author_rank: Regular Contributor
timestamp: April 14, 2017, 08:14:58 am
content: They are used to check police radar guns.http://www.pbelectronics.com/radar_tuning_fork.htmNote:When I was working on project of Doppler radar I have had an opportunity to verify it's functionality and in lack of tuning forks I used a small speaker driven by sinusoidal oscillator.Georg

author: CustomEngineerer
author_rank: Frequent Contributor
timestamp: April 14, 2017, 11:20:34 am
content: Quote from: ebastler on April 14, 2017, 07:10:18 amMuch interest

author: ebastler
author_rank: Super Contributor
timestamp: April 14, 2017, 12:59:13 pm
content: Quote from: CustomEngineerer on April 14, 2017, 11:20:34 amHappy to oblige, thanks for the interest!Here's the Lo-15 in all its beauty, and the "Allstrommotor" (all-current motor). The flat drum on the motor axis, with the black and white stripe marks, contains the centrifugal governor; motor current is routed via the two copper traces around its circumference. The governor setpoint is changed by rotating the little rubberized wheel which protrudes from the drum's face. By pushing the chromed levers on the front or the back side of the can against this wheel, it can be adjusted while the motor is running.The tuning fork is quite sizable; 9V battery shown for comparison. The fork is tuned to 125 Hz, giving 250 "strobes" per second when peeking through the slits.

author: frozenfrogz
author_rank: Frequent Contributor
timestamp: April 14, 2017, 02:07:43 pm
content: Quote from: ebastler on April 14, 2017, 12:59:13 pmThat is one pretty machine!I had to search the web to understand it is an old Telex and founda nice scan of the original manual.Is the tuning fork acting as a timing device for sending and receiving (like a quartz oscillator would), or is there a totally different purpose?Thanks for sharing btw

author: ebastler
author_rank: Super Contributor
timestamp: April 14, 2017, 02:27:06 pm
content: Yes, I still enjoy looking at that old teletype (and occasionally starting it up -- it's connected to an embedded Linux board running Zork and other text adventures).The Lo-15 is essentially a fully mechanical device. The only two electrical components are one solenoid, to convert the incoming serial signal into movements of a little lever, and the motor to drive the various mechanisms. Encoding the key presses into a serial data stream, converting incoming serial data into 5 parallel bits and typing the right character, decoding the various special characters (CR, LF, BEL, letter/digit switching, ...) are all done in mechanics, via camshafts etc.. No relays or other newfangled technology!My unit is probably built in 1954, but the design dates back to 1930. The Lo-15 was built under license from Teletype Corporation, and is an exact copy of their Model 15 -- the only change is that all threads are metric.The tuning fork is not part of the teletype itself, but of the service kit. It is used to adjust the motor speed during maintenance, to make sure all machines on the network are running at the same data rate. The data rate is not that critical, since asynchronous transmission is used. (Each character begins with a start bit that triggers the serial/parallel conversion mechanism on the receiving end, just like in RS-232. So the machines only need to stay in sync over the duration of the 5-bit character.) The tuning fork's cardboard box is optimistically labelled "125.000 Hz" though.Edit: Typos

author: jpanhalt
author_rank: Super Contributor
timestamp: April 14, 2017, 02:48:59 pm
content: The two types you show in in pictures 2 and 3 can be used in physical diagnosis of patients with sensory losses. The one with the flat for holding is possibly modified specifically for that purpose, but any of those type will work. You can distinguish nerve deficits from conduction deficits, as in hearing. They are still used for that purpose.While not a tuning fork per se, the first "electronic" calculator I used in physics (circa 1965) used a vibrating rod for memory.John

author: frozenfrogz
author_rank: Frequent Contributor
timestamp: April 14, 2017, 02:53:18 pm
content: Thanks ebastler for clearing that up.The use of a tuning fork with mounted slit diaphragm for optical tuning is quite ingeniousI love, how low tech devices can be used to solve delicate problems!

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 14, 2017, 03:30:14 pm
content: Many of the tiny gyroscopes made on silicon are fundamentally tuning forks. Systron-Donner made (still does I think) a slightly larger version that is more explicitly based on a small quartz tuning fork (centimeter size). Somewhere in my parts pile I have one of those that just needs me to cobble up the drive electronics.

author: albert22
author_rank: Regular Contributor
timestamp: April 14, 2017, 04:28:51 pm
content: ebastlerQuoteBeautifull.!!!TNX

author: IdahoMan
author_rank: Regular Contributor
timestamp: April 14, 2017, 05:27:39 pm
content: Cool. Thanks for sharing, ebastler.

author: ebastler
author_rank: Super Contributor
timestamp: April 14, 2017, 06:01:54 pm
content: Hey, glad you guys liked this -- so I'm not the only one fond of "heavy metal" communications technology!As an encore, here's a closeup of the teletype's keyboard. (But I'll stop after that one, since the rest of the machine has nothing to do with tuning forks...)My favorite is the mechanism above the right-hand part of the keyboard, behind the '7' to ')' keys. That's the automatic ID transmitter. When installing the teletype, the operator would encode the station name there, clamping little metal tabs to the perimeter of the small drum for each '1' bit. This ID could then be sent simply by pressing the "Hier ist" (this is) key on your own device -- or you could ask the remote station to identify itself, by transmitting the "Wer da" (who's there?) control character to the other station.The remote ID works even if the machine on the other side is unattended; receiving the "wer da" character automatically starts the ID transmitter. Again, the whole thing is purely mechanical: There's a camshaft with 5 cams to the right of the character encoding drum, which causes little gooseneck-shaped levers to dip down and sense the pins on the drum bit by bit, before the drums turns by one step, on to the next character.'nuf said -- back to tuning forks! I learned about their use in General Radio oscillators and in viscosity meters in this thread. Thanks to all who posted, and especially to IdahoMan for starting a stimulating thread!

author: cvanc
author_rank: Frequent Contributor
timestamp: April 14, 2017, 06:29:25 pm
content: Quote from: frozenfrogz on April 14, 2017, 02:53:18 pmAgreed! Very cool 'old school' solution to the problem.

author: CustomEngineerer
author_rank: Frequent Contributor
timestamp: April 15, 2017, 01:46:40 am
content: Beautiful pictures and especially thanks for explaining how they function. Very interesting indeed.

author: ebastler
author_rank: Super Contributor
timestamp: April 17, 2017, 09:28:14 am
content: Quote from: ebastler on April 14, 2017, 02:27:06 pmCuriosity got the better of me -- were they really serious about those three decimal places?Probably not. As of today, the frequency is a bit more than 0.1% too high, measuring the vibration at the fork's stem via a microphone. Still, not too bad for this low-tech standard; and much better than what is needed to adjust a teletype motor!

author: metrologist
author_rank: Super Contributor
timestamp: April 17, 2017, 07:48:46 pm
content: A tuning fork can be used as a medical instrument. It can determine if someone has conductive hearing loss by touching the base of the vibrating fork against the patient's skull, and if they can clearly hear the tone being transmitted through their bone, then their hearing nerve is still functional and hearing loss may be an issue with the ear drum or middle ear.

author: mmagin
author_rank: Frequent Contributor
timestamp: April 17, 2017, 09:41:07 pm
content: Quote from: edpalmer42 on April 14, 2017, 05:06:56 amI have one of those too. Technically I think the carbon microphone elements used could be considered active devices of a sort.Mine doesn't quite work well at the lower supply voltages, I wonder if it's suffering the same problems as old telephone microphones where moisture gets in and causes undesired clumping in the carbon particles.It has the typical whitish surface corrosion on the tuning fork associated with cadmium plating too.

author: edpalmer42
author_rank: Super Contributor
timestamp: April 18, 2017, 02:37:47 am
content: Quote from: mmagin on April 17, 2017, 09:41:07 pmNnnoooooooo! You weren't supposed to let the secret out!I don't think I've ever heard a carbon mic described as an active device, but it's certainly substituting for one.QuoteWhen that happened to a phone, the standard repair procedure was to bang the handset hard on a table or something similar to break up the clumps. I wouldn't recommend something that violent, but maybe some tapping on the cartridge would help. You might also try exchanging the two cartridges. It's also possible that the cartridge adjustment needs a tweak.QuoteThe plating was basically gone in mine. The only thing left was white fuzz so I disassembled it and cleaned off as much as I could.Ed