Wednesday

23.12.2020 Gent's Bell-ringer Contacts.

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I was asked, in the comments section, to share some images of the Gent's Bell-ringer contacts.  Bell-ringers were commonly used in schools to provide accurate and universal timing of classes.

The contacts vary in number, but my own, single circuit contacts are shown here. Multiple contacts were supplied, to order, by Gents. To allow individual bell ringing circuits. Perhaps for use in different areas of a building or complex.

 

 

Note that there are two distinct sets of contacts:

The lower set are situated left of the centre of the movement. They are actuated by a cam and offer weekend silencing. Or any other silencing period with a suitable cam. Slots in the day of the week wheel allows some adjustment by loosening the visible screws.

These contacts are normally CLOSED. If they are open then the bell system is silenced.


 
 
The second set of contacts are activated by tapered pins inserted into the 24 hour wheel. These contacts are found at upper left of the bell-ringer movement. Fitting pins in specific holes will allow a day and night choice of electric bells being rung as frequently as small fractions of any hour. These contacts are normally OPEN.   When a pin comes around it lifts the shaped, brass, contact actuator. The circuit is then closed until the pin moves on and releases the contacts again.   A tilting mercury switch limits the duration of the bell circuit to a few seconds to avoid tedium. A toggle switch is provided to silence the bells. While a push button is provided for alarms, drills, etc. Naturally the contact system can be used for other timing purposes.                                                                                      
WARNING! Be VERY careful in your choice of pins if you need more or lack any at all. I bought some large, standard, tapered clock pins and found them too long. Not having noticed this problem immediately, they completely locked up the bell-ringer movement. A pin had jammed against the frame. I had to clip off the shiny new pins to a safe length and then round the ends neatly over again. 
 
 
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My apologies for the poor layout of this post. After years of practice, Google Blogger has finally and completely ruined the familiar editing and composition features of blogger. They caused this with an "update" aimed primarily at mobile phone users. I took the provided option to reject the change and continue with the original blog format. Only to find that I was now being punished for my recalcitrance. 
 
It is no longer possible to drag and drop images or text or even to expect auto justification of text around images. Hence the large gaps where text should normally exist! I have had to use "jump break" to keep the text in a relevant position beside the images. 
 
They ruined the HTML editing facility too. So it is no longer possible to undo the damage they cause in standard composition. WYSIWYG. Remember that these incompetents are largely in charge of the world these days. Though you are not provided with a vote to get rid of them.
 

 
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1 comment:

John Freeman said...

So the logic diagram shows that the bells ring if the over-ride switch is 'on', weekend switch is 'on', the 5 minute timed switch with pins is 'on' and the mercury switch is 'on'. The reason for the mercury switch is that the 5 minute timed switch is not sufficiently accurate - in fact it is closed for about 5 minutes for each pin.

Beyond the excellent standard engineering, he interesting element for me is the mercury switch, which is cleverly designed such that the switch is open almost all the time, and at each five minute mark, the mercury switch drops, all the mercury floods to the left and closes the circuit, and over a few seconds the mercury flows through the constriction to the left hand bulb. Over the next four minutes the mercury switch tilts bit by bit, and the mercury flows to the right hand bulb, crucially in a way that does not make the circuit. It is only at the five minute mark that the mercury switch drops, and the circuit is made as above.

I've added an over-ride switch to my bell-ringer so that a light (in my case) can be illuninated every five minutes for a few seconds, thus enabling better demonstration of the mercury switch operation.

John Freeman