Ringing waveform

Had a play, still can't see how it is supposed to work, there is no 25Hz component of the input waveform to 'filter out'. And all the diode will do is make higher harmonics. The circuit in Atkinson will work, it has an 'active device' (the relay) selecting every 3rd peak.

[Dave Moll]

If it selects every third peak, presumably it's producing 16⅔c/s - which was also used for ringing current - rather than 25c/s.

It does indeed produce 16 2/3rds.

[russell_w_b]

Ask auntie Google about magnetic frequency dividers.
https://books.google.co.uk/books?id=...ircuit&f=false

Thank you Russell, thought I was missing something. Very interesting indeed.

[Top Cap]

Many years ago I was asked to make a digital 'ringing' generator and given the spec waveform required. It appeared to be like a sharks fin (see rough sketch) where there was a slow rising voltage then an abrupt collapse. At the time I was told that the waveform was similar to the rotary machines in the exchange that normally fulfilled the task. I think I used some op-amps and simple zero crossing detectors to achieve same, it was a long time ago .

[russell_w_b]

Your 'shark's fin' is heading on towards what a simple, two-pole magneto generated ring voltage looks like. Here's my type 26A in action on a 59A bell-motor. Nice and peaky to make those bells 'ting'!

[lesmw0sec]

Originally Posted by russell_w_b

What you want is Atkinson, Volume 1 (September 1947 but reprinted and available).

I have one of those units tucked away somewhere, from an old farm installation.

Incidentally, most old telephones will ring quite well at 50 c/s and I once built a small exchange using a square wave from a semiconductor bridge circuit. I could detect no difference between that and the normal ringing waveform.

Les.

[russell_w_b]

Originally Posted by lesmw0sec

I could detect no difference between that and the normal ringing waveform.

Interesting that, Les, and I suspect that it sounded OK because of the square wave you produced. 50Hz sine wave is not so clever, I've found, although there is an official GPO modification to alter some bells to run at 50 Hz via 'Transformer, 92B'.

At 16 2/3 Hz, the impedance of the bobbins is less than it is at 25Hz, and way less than it is at 50Hz. At 16 2/3Hz, the phase angle is 41 degrees which is near the 45 degrees where most power is developed. I think a 'peaky' waveform on the polarised bell motor works best.

Really early bell motors were designed for a third of mains frequency rather than a half of it.

[KW2000A]

UKCOL...you were most fortunate. When I joined we were Technicians in Training...

[dagskarlsen]

The fine thing about standards is; the number of standards are so great, you will always find a standard to fit your needs.

This thread contains references to practice, and standards from many countries. Today some countries just use the same frequency as the power grid. Most European countries has used 25 Hz. USA has mainly used 20 Hz. The wave form was not an issue until this became easy to analyze. Some countries has used ringer tuned to various frequencies. Still most ringer was not made sensitive to frequency variations within a great percentage of whats normal. By experience 15-35Hz would work, but not always sound familiar. Even 50 hz sould be possible after some minor mechanical tuning.

As someone has stated over. The Wave form, and frequency will give different loads at the same voltage, and with the same capacitor. If this is of practical importance depends of the complete setup.

If we try to set up all these parameters in a system, at least for me, it ends up to be far to complex. I'am ending up as many others with generalization, and making my own simplified rules.

E.g. for non selective (normal) ringers.

1 If it works, do not change it.
2 If it works like someone lifting the receiver, and hanging up, it use to much current, add capacitor or resistor in series until this problem stops.
3 If the ringer warbles, but not ring, adjust mechanically.
4 If it is absolutely no reaction on ring signals, look over the mechanical, and if needed electrical for things blocking the function. (Defect capacitor, coil, wires and connections.)
5 Still no function, remove from telephone and do the tests and diagnostics on the bench. Test with different capacitors, ringers etc to locate what part to be changed/repaired.

As a power-supply I used to use a 50Hz 30V transformer, until I got a transformer giving out 25Hz 75V. (I still do not know the wave form, but it was used for telephone ringers)

dsk

[Oldcodger]

Going back to the ye olde ringing machines in UAX's ,I seem to remember the figure of 17HZ interrupted mechanically (I think) 20 times a second.

[dagskarlsen]

Since i do not see any good in the investment of a true oscilloscope, I downloaded the SW for using the pc sound-card, and 25 Hz is definitely on the edge of what to observe with great accuracy. a little film of the scope, when ringing with my 1946 electromechanical PAX generating ringing at 25Hz by a vibrator. It looks like sawtooth.
I shall try to encl the film and a picture of a narrow part of the ring.
dsk

[dagskarlsen]

Her is the film
http://tinyurl.com/ngx4yxp or https://www.youtube.com/watch?v=Q-W8bolEgGA

Thanks all for the information (and waveforms dags) I think I am going to go for a 0..50..100 volt PSU and switch from 50V (line on hook) to 0V and 100V at 25Hz with a 25% duty cycle, so that will be 10ms of 50V then 0V then 50V then 100V then 50V. For simplicity the first implementation will be done with reed relays (and more than likely, if it works, stay that way).

[Hartley118]

Interesting and informative discussion. When I worked for Post Office Telephones as a vacation job many moons ago, ringing current was referred to as 17 c/s, but was actually 25 c/s (Hz) generated by a little motor alternator mounted in one of the racks in the main exchange and running from the main 48V battery supply. No way could the GPO allow their ringing current to be interrupted by a mere failure of the AC mains!

I remember being surprised that such a small machine could supply all the simultaneously ringing phone bells in the town.

Martin

[dagskarlsen]

The ring cadense of my old exchange are just made of a circuit of a relay, and a capcitor, maybe a resistor. The vibrator sends out pretty stable 25Hz (+/- 0.5 Hz). The voltage measured at the phone is about 75 V. You may find some more info about my PAX here: http://tinyurl.com/nc868xc.

dsk

[dagskarlsen]

One more hint; these works: http://tinyurl.com/nj9roo7
dsk

[Oldcodger]

dags - just one other addition to your excellent post #31- if you fit an instrument to a PBX, and it does not ring, try it on another line(e.g an exchange line from the local exchange), as not all PBX send out ringing current at the same frequency ,and not all instruments will ring on frequencies outside their design range.

[BottleMan]

Gents

You might be interested in this article from Texas Instruments.

http://www.ti.com/lit/an/slua060/slua060.pdf


Graham