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December, 1951

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"Self Service." for many years a feature associated with acid lamps, is now becoming general, in one form or another. Its objects are to render the distribution and handing in of lamps possible without delay, and with the least possible handling. Queues of men at distribution hatches are avoided, and the lamps receive no abuse by being thrown or roughly handled along the receiving benches. It is a regrettable fact that, in not a few old-type installations, batteries suffered due to unnecessary rough handling of the lamps almost as much in the lamproom as they did underground.

The lamproom staff, being thus relieved of the responsibility of handing out and receiving lamps, can thus devote their whole attention to charging and maintenance. Their routine then consists of (a) placing lamps on and off charge; (b) topping up batteries; and (c) carrying out the photometric check.

As applied to the acid lamp, self service relieves the lamproom staff of the necessity for putting lamps on and taking them off charge, this operation being performed by the user when he places his lamp on the frame and takes it off again, at either end of the shift. A low-voltage constant-potential charging system is used in which the lamps are connected in parallel, and these, being of one-piece construction, are not dismantled. The charging circuit is completed, in the case of the Oldham lamp, through the headpiece upon turning this round clockwise through an angle of 180° on its peg. Current then flows and is determined by the state of charge of the battery, the applied voltage being maintained constant at 4.9 V. The charging current thus falls as the battery approaches full charge. (Figs. 24 and 25.)

The Youle lamp, which incorporates a rectifier in the headpiece, can be charged directly from an alternating supply, a double-unit step-down transformer being fitted on the charging rack to bring the voltage down to the desired low value.

In the self-service systems applied with the lead-acid lamps the duties of the lamproom staff are confined to the examination of the lamps on the charging frames and to the necessary periodic topping up and photometric testing. Topping up is done by the use of trolley-mounted equipment, and the photometer is also carried round to the lamps on a trolley, when required.

In contrast with these low voltage, constant-potential, charging systems, the alkaline installations, which are illustrated in Figs. 26, 27, 28, 29 and 30, employ the series charging method, the batteries being connected in series and the voltage of the charging circuit being varied to give a constant-current feed. Access to the charging circuit is therefore not given to the user of the lamp. Self service in this case is confined to the handing in and the taking out of the assembled lamps. The responsibility for charging the batteries falls entirely on the lamproom staff, and the lamp user takes no part in it. Charging of the batteries is effected by unlocking the lamps and removing the battery to a charging position which is immediately adjacent to the storage position. No large-scale movement of lamps across the lamproom is involved. When the charging of the batteries has been completed, the lamps are reassembled and placed in their storage position there to await collection at the start of the next shift. Topping-up equipment, unlocking magnet, and photometer may be carried round to the lamps on trolleys, as required.

Maintenance of batteries

Lead-acid batteries are far more easily ruined by neglect or ill usage than are alkaline cells, and it is therefore extremely important that they should be used and maintained intelligently.

When given the best possible treatment and attention, the life of an acid lamp will probably be relatively short compared with alkaline types, although it can be replated, on the average, twice, during its lifetime. The cost of maintenance of acid batteries, and their rate of depreciation, therefore compares unfavourably with alkaline batteries, but on the other hand, their initial cost is very much less. There is a marked advantage for acid-type cap lamps on the score of weight, but this advantage has been reduced by the introduction of the plastic-cased alkaline battery. If a choice must be made between the two it is necessary to balance the high initial cost of the one against the lower first cost but more rapid deterioration of the other, since there is little to choose between either from the illumination standpoint. Experiments to compare various installations under the same conditions would be needed to find where the ultimate advantage lies.

Lamproom staff

It is evident that the proper maintenance of good illumination from portable lamps at a minimum cost to the industry depends upon the efficiency with which the lamproom staff operate. More attention is now given to this aspect than was at one time commonly the case, and it is now recognised that lamproom personnel should be trained men. What form their training should take is a matter for consideration. It would be interesting to have the views of the responsible engineers in the industry upon the desirability or otherwise of continuing the training of lamproom staff, on the lines of the Nuneaton Staff College, which is now closed down, on a Divisional basis.

Lamproom photometers

Photometric measurements in the lamp room consist of the simple operation of noting the deflection registered on a microammeter which is coupled to a photoelectric cell attached to some form of photometric sphere or box. The headpiece of the lamp under test is held against a window in the box, so that it shines its beam into the interior of the apparatus. The micro-ammeter is calibrated to read M.S.C.P. directly, and no conversion factors or calculations are required. The original calibration of the apparatus is made against a standard instrument in the manufacturer's laboratory, and it is advisable that the lamproom instrument should be checked periodically in order to ensure that its calibration remains true. For this purpose the Area and Divisional scientific staff should take on the responsibility of maintaining lamproom photometers to standard, and it is necessary to have a standard instrument located at a central laboratory from which sub standards can be made. These sub standards can then be taken round to the pits for comparison with the various lamproom photometers. Re-calibration of photometers should be performed at intervals not exceeding six months in length, and those photometers which have an interior coated with white paint should be repainted at intervals of one year with a standard photometric paint.

Design of lamprooms

Much could be said on the layout and design of lamprooms, but on this occasion it is only possible to give typical examples. Figs. 33 and 34 show a self-servicing layout for 1,000 acid cap lamps. Access to both sides of the charging frames is available to the workmen as they pass through the lamproom in a one-way stream, to pass by the control point which is situated near the exit. Separate provision is made for the flame safety lamps which are required.

Figs. 35 and 36 illustrate examples of an alkaline installation. Access by the workmen is here confined to the storage side of the frames, which are arranged in island pattern, so that the charging equipment is quite separated from the storage side of the frames. Only the lamproom staff operate within the island. As in the previous example, a one-way passage is enforced, and provision is made for the distribution of oil lamps where necessary.

Fig. 37 shows another example of an alkaline installation in which the servicing room is built within the lamproom proper. The charging racks are placed in the centre of the building with a wall of self-service storage cubicles running down either side. Each cubicle is numbered and the miner, who proceeds through the corridor formed between the lamp room outer wall and the storage cubicle units, collects his lamp and continues through the room to the pit head. At the end of the shift, the miner re-enters the corridor and places his lamp in his number ed cubicle, and the lamproom staff, operating from the inner side of the storage cubicle units, unlock them and place the batteries on an adjacent charging rack. After servicing and charging, the lamps are returned to the same cubicle ready for collection by the miner when he returns to work, as shown in Fig. 38.

Future developments

It has been said that, owing to the limitations of weight and size, portable electric safety lamps have reached finality in design, but this can hardly be so. In the near future, we can look forward to the introduction of acid lamps employing 4 V. 1 A. bulbs, and to the further development of alkaline lamps fitted with a four-cell battery and a 4.8 V. 0.8 A. bulb. These will result in a much greater output of light than can be obtained from the lamps available at the present time.

It is not inconceivable that revolutionary changes in the traditional design of cap lamps may one day be made. For example, why should not the headpiece be made integral with the helmet ? Such an arrangement would at least ensure that the lamp was always worn in the correct place. Again, the weight of the battery could more easily be taken on the back or on the chest, and in either of these positions would cause less inconvenience to the wearer than it often does when carried on a belt. The shorter length of cable required would also be advantageous. Why should we not have alternative designs of cap lamp to suit various types of work?

There is also the probability that it may be possible to set up charging stations underground. This will facilitate the adoption of larger semi-portable lighting units which could be employed as floodlights where no mains power is available. Many of the difficulties associated with mains lighting at the face arise because of the necessity for dismantling and moving forward the equipment as the face advances. These difficulties would not exist if battery lamps were used.

Conclusion

There is a very important part to be played by portable electric lamps in the illumination of mines, and the increasing application of mains lighting does not mean that portable lamps will one day be obsolete. Efficient lamps, easily capable of conforming to the highest statutory standards are available, either acid or alkaline types, and maintenance of the lamps to retain good lighting efficiency is facilitated by systematic lamproom organisation in which photometric control is the key to successful and effective results. Adequate training of the lamproom staff is a necessary complement to the installation of scientific control methods, and without this even the best equipment will be of little avail.

Drawings and Photographs accompanying the article