ATM MINING TELEPHONES (UNDERGROUND)

Automatic Telephone and Electric Company. Ltd.

Melbourne House, Aldwych, W.C.2.

Strowger Works, Liverpool, 7.

MAGNETO MINE TELEPHONES

Intrinsically Safe Type Certified by The Mines Department, Certificate No. T/Tel/8.

The Coal Mines Act of 1911, Section 54, Regulation and Order 103, states, "Where in any Mine, not being a small Mine, the distance of the main haulage from the shaft exceeds 1,000 yards, efficient means of telephonic communication shall be provided and maintained between the end of the main haulage and the pit bottom and the surface."

The certified A.T.M. Magneto Mine Telephone caters for the requirements of Intrinsic Safety and F.L.P. Flameproof enclosure in accordance with Colliery Regulations only, and has been granted the appropriate certificate by the Mines Department of Great Britain. The performance of this telephone for ringing and speaking is excellent. When two are connected in series with an adjustable resistance, satisfactory ringing and speaking is provided through 3,000 ohms and 10,000 ohms respectively.

The specification is as follows :-
Particularly robust and of compact design. Broad machine-faced flanges on the cast-iron case and cover, and on inner terminal compartment and cover, render the telephone flameproof. Either two armoured cable glands or one gland and sealing plug are supplied to customers' orders. The size of cable for which the glands are required should be specified when ordering. When installed the cables must be sealed in the glands by means of plastic compound. The cover is secured by triangular headed bolts, and is only removable with the special key. It is bodily detachable without disturbing the fixed electrical connections. A terminal compartment protected by an inner cover accommodates the terminals and provides for the entry of external wiring. A five magnet generator is fitted, and the telephone is adapted for bridging work. The generator mounting is adjustable for accurate alignment with the driving handle, which is counterbalanced. The loudspeaking receivers are metal cased, and the connecting cords protected by braided steel armouring, securely anchored to glands at each end. The polarised magneto bell is housed in a separate compartment, and can be removed without disturbing fixed connections. An approved Mines Department condenser is fitted across the ringer terminals. All components are readily accessible for inspection, adjustment, or removal, and the electrical insulation throughout is of a high order. A box spanner is supplied with each telephone. Highest grade transmitter. Finish : Dark green enamel.

T.3035. Magneto Mine Telephone. Fitted with one receiver. Height 2ft 3in; width 15.5in; depth 7in; weight 83lbs.
T 3036. Magneto Mine Telephone. Fitted with two receivers, otherwise specification and dimensions as T.3035. Weight 85lbs.

F.L.P. TYPE
Prices for the T.3035 & T.3036

Fitted with two glands £13.7.0 or £14.11.0
Fitted with one gland and one plug £12.19.0 or £14.3.6

When required for intrinsically safe conditions only, glands are unnecessary.
Price without glands £12.12.0 or £13.16.0

SOME OUTSTANDING FEATURES OF THE A.T.M. MAGNETO TELEPHONE

• The Ringer Assembly can be readily withdrawn for inspection or replacement without removing any electrical connections.
• The Induction Coil is removed by merely unscrewing the fixing screws, as all the electrical connections are made on the auxiliary mounting base.
• The Generator is easily removed as there are no soldered connections.
• The connecting wires of the Safety Shunt across the Generator are indestructible, being of plaited copper wire construction.
• The Generator Handle cannot be removed until the instrument is opened by the special spanner provided, thus preventing interference by unauthorised persons.
• The Cable Glands can be made off and sealed before being attached to the instrument, thus facilitating connecting up.
• Mild steel bars are used for mounting the instrument, as it has been found that extended cast lugs are easily broken by the rough usage to which equipment is usually subjected in collieries.

CERTIFIED SURFACE TYPE MAGNETO TELEPHONE
Mines Departrnent Certificate No. T/Tel/8. Wall Pattern

This Telephone is certified by the Mines Department as being intrinsically safe for surface use only, and is suitable for inter-connection with any approved magneto telephone system, the generator being fitted with a non-inductive shunt and the ringer shunted by an approved condenser. It is fitted with a hand microtelephone of the B.P.O. standard design, incorporating an approved design of transmitter.

T.3904 Wall Pattern Surface Type
The case of this telephone is designed to hold the two dry cells for speaking purposes, thus making a self-contained unit.

Height 11in; width 11in; depth 6.5in;
Weight 12.5lbs
Price : £6.1.0

CERTIFIED SURFACE TYPE MAGNETO TELEPHONE
Mines Department Certificate No. T/Tel/8.

Desk Pattern T.3903
This Telephone is certified by the Mines Department as being intrinsically safe for surface use only, and is suitable for inter-connection with any approved magneto telephone system, the generator being fitted with a non-inductive shunt and the ringer shunted by an approved condenser. It is fitted with a hand microtelephone of the B.P.O. standard design, incorporating an approved design of transmitter.

Height 10.5in; width 10in. depth 6.5in.
Weight 12lbs. Price £6.1.0

Two-cell Battery Box for T.3903 Telephone (T.4651A)
Oak cover polished finish with hook and eye fastener.

Height 4.5in. width 3.75in. depth 2.5in.

Needs two T.2190 Dry Cells for T.3903 Telephone

A.T.M. TELEPHONE COUPLING UNIT (For Intrinsically Safe Telephone Systems) Type
Certified by The Mines Department, Certificate No. T/Tel/52.

The A.T.M. Mine Telephone Coupling Unit T.3993 is a very definite improvement over all other types available in so far that it permits through speech and through ringing, has no moving mechanism, requires no maintenance, and does not require manual switching. It employs the conventional series impedance network, but is shunted on the "in-bye" or "safety" side by an "Atmite" disc.

The purpose of the "Atmite" disc is to limit the voltage across the "in-bye" connections to the "safe" circuit whilst permitting the application of any potential to the "unsafe" side. The connections to the "Atmite" disc are made in a novel manner so as to disconnect the circuit to the "safe" side should the disc itself become disconnected at any point. It is thus impossible for an incendiary potential to be applied to the "safe" side of the coupler even if the disc becomes disconnected.

A typical result of a test made of the A.T.M. Coupler employing an "Atmite" disc, is as follows:- With a maximum possible speed of hand turning of a generator with a peaky output giving a maximum recorded R.M.S. of 110 volts and a maximum peak of 300 volts, the voltage and current on the "safe" side were:- With one bell with safety condenser, 25 volts, 3 m.a. With six bells with safety condensers, 25 volts, 12 m.a. The attenuation to speech on a 600 ohm circuit was less than 0.1 decibels.

* "Atmite " is a mixture of silicon-carbide-molybdenum with a ceramic binder, pressed and fired, and has a non-linear resistance.

Length 7.5in; height 6.5in; depth 3in.
Weight 12lbs 8ozs
Price : £4.10.0

Taken from the A.T.M. Mine Telephones and Signalling Equipment Book - April 1939

Last revised September 08, 2003