ATM TELEPHONES T.3035 & T.3036
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 :-
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.
Fitted with two glands £13.7.0 or £14.11.0
When required for intrinsically safe conditions only, glands are unnecessary.
SOME OUTSTANDING FEATURES OF THE A.T.M. MAGNETO TELEPHONE
Two-cell Battery Box for T.3903 Telephone (T.4651A)
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
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.
Taken from the A.T.M. Mine Telephones and Signalling Equipment Book - April 1939
Last revised: October 06, 2012