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In order to make it possible to communicate between different departments and rooms in large establishments, such as warehouses, factories, or offices, without the aid of a telephone exchange, intercommunication instruments have for a long time been in use. These instruments have been made of various patterns, but it is common to all of them that one instrument can by means of a simple manipulation on the instrument itself be brought into communication with any other instrument on the same installation.

We have for some time past been making instruments of this description, but as the demand has largely increased lately we have found it necessary to devise a new system, which we claim is a decided improvement on the old ones, and which we are sure will give every satisfaction.

The instruments are manufactured for installations of  10, 15, 20, 30, 40, 50, or 6o lines, and they can properly be divided into two groups, viz., instruments for 10, 15 and 20 lines, and instruments for 30 lines and upwards.

The first-mentioned pattern is partly made with the switch and the telephone instrument combined, and partly with the switch fitted separately. In either case the switching is done by turning the pointer of the switch to the number required. When the instrument is not in use the switch should be left in its normal position, which is marked A.

The latter pattern is made with the switch separate from the telephone instrument. The switch is fitted with one spring jack for each line, and also with one jack A (normal position), and a plug and cord for switching. A connection is effected by placing the plug in the jack of the line required. When not in use the plug should be inserted in the jack marked A.

A most important improvement is that the numbers on the switch run consecutively, so that all instruments are exactly alike. There are several other improvements in the construction, in particular, if the switch or plug, as the case may be, is not returned to the normal position A, the bell of the instrument will still ring if a call is made from any of the other instruments. The call can, of course, not be answered until the pointer of the switch, or the plug, is in the position A.

Another point is that, if either of the two persons connected omits to return his switch or plug to A, and a third person calls, only the bell of the called instrument will ring, the other one being cut out.

With regard to the lines, our intercommunication instruments can be divided into two distinct groups, viz., instruments working on single lines with a common return, and instruments working on metallic circuits. In installations of twenty or more stations, or when the lines are of considerable length, we strongly recommend the use of metallic circuits. When several conversations are going on simultaneously on a single line system, overhearing by induction between the lines is rather bad. This drawback is absolutely overcome by the use of metallic circuits.

The price of metallic-circuit instruments is only slightly higher than that for single line ones. The cable used for metallic line instruments consists of twice as many wires as are required for single line instruments, the increase ill price, however, is not very considerable.
Instruments for more than twenty lines are only made for metallic circuits, but they call, of course, be used on single lines if required.  If desired, single line instruments are made to order.

Inter-communication instruments are made both for battery and magneto ringing.

The chief advantage of battery-ringing instruments is the convenience of only having to press the button when giving a signal. Oil the other hand there are several disadvantages, one being that the ringing battery has to be renewed periodically, and that the signal is unreliable if the insulation of the cable has been damaged through damp or mechanical injury.

For these reasons magneto-ringing instruments have lately been used more and wore, and we particularly call attention to the advantage, not to say necessity, of using this system of calling for large installations with long lines.  Should an installation be required for less than ten lines, or for a number not found in our Catalogue, the instrument for the next higher number should be used and the surplus numbers left blank.

In most cases it is advisable to have a few spare numbers, as the first cost is only slightly increased, and to change the whole system for one or two lilies afterwards found necessary involves a heavy expense, as all the instruments would have to be taken out and replaced by others for a larger number of lines.

Inter-communication instruments are divided into the following groups, viz.

  1. Battery-ringing intercommunication instruments for 10, 15, or 20 single lines.

  2. Battery-ringing intercommunication instruments for installations with 10, 15, or 20 metallic lines.

  3. Inter-communication switches for 10, 15, and 20 metallic lilies, to be used in connection with magneto-ringing telephone instruments.

  4. Inter-communication plug switches for 30, 40, 50, or 6o metallic lines, to be used in connection with magneto or battery ringing telephone instruments.

Battery-Ringing Inter-Communication Telephone Instruments for Installations of 10, 15, or 20 Single Lines
These instruments include both the switching, arrangements and the telephone instrument. The switch is provided with a handle and pointer, to be placed oil the number required, a trembling bell, a press button S (on the left-hand side of the instrument) for ringing, and a press button T (on the right-hand Side of the instrument), by means of which two instruments engaged in a conversation can be connected with each other by two separate wires instead of using the common return wire. There is also fitted a hand micro-telephone, with a key in the handle, and an induction coil.


To Make a Call.

  1. Place the pointer of the switch oil the required number.

  2. Press the ringing-key S.

  3. Remove the hand micro-telephone from the hook, put and wait for a reply.

  4. When finished, restore the switch to its normal position, with the pointer on A, and hang up the hand micro-telephone.

To Answer a Call.

  1. When the bell rings replace the switch to A, if this is not already done.

  2. Take the hand micro-telephone from the hook and reply.  During conversation the key in the hand micro-telephone should always be pressed down.

  3. When finished, hang up the hand micro-telephone.

If the persons conversing should find that the induction from other lines is troublesome, this call be remedied, to a considerable extent, by the called subscriber turning the pointer of his switch to the originating subscriber's number, and both of them keeping the keys T pressed down as long as the conversation lasts.

Battery-Ringing Inter-communication Telephone Instruments for 10, 15 and 20 Metallic lines

These instruments are very similar to those for single lines and include both the switch and the telephone instrument.  The press button T is, however omitted, because the instruments are constructed for metallic lines.

Inter-Communication Switches, for 10, 15, and 20 Metallic Lines, to be used in connection with Magneto-Ringing Telephone Instruments

These instruments include the switching arrangements only, and are to be used in connection with magneto-ringing telephone instruments. They are only made for metallic circuits. The switches are provided with a pointer, which, in the normal position, should point to A, and the switching is done by turning the pointer to the number required.

The manipulation of the instruments is exactly the same as already described under Group 2, except that the calling is done from the attached telephone instrument,

Inter-Communication Switches, for 30, 40, 50, and 60 Metallic Lines, to be used in connection with Magneto or Battery Ringing Telephone Instruments

These switches are constructed for metallic circuits, and include one jack for each line, a home jack A, and a cord with plug for switching. When the switches are not used, the plug should be placed in the home jack. The calling of a certain line is effected by inserting the plug in the corresponding jack, the signal being given from the attached telephone instrument.

The manipulating of these switches is exactly the same as already described under Groups 1 to 3.

Taken from the Ericsson Telephone Catalogue 1903

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Last revised: March 26, 2024