Working groups
     Usually an instrument mechanic works under a foreman (who is himself under the direction of the instrument maintenance engineer) and a chargehand, who from his experience of the work is able to advise on how it should be done. On the job each mechanic usually has a mate, who is a semi-skilled man. He may also have an apprentice, whom he helps and gives the benefit of his experience. In a modern power station where there is full-scale instrumentation there are about half a dozen instrument mechanics, but this number is likely to grow with the increasing complexity of automatic control systems which are being developed.

Boiler house instruments
     Some of the types of instrument used in the boiler house are: direct vision, gauge-glass, float-operated, electronic: these measure liquid levels. Instruments such as the ‘U’ tube or the Bourdon gauge are used to measure the pressures of steam, water, flue gases, air (from induced- and forced-draught fans). A further set of instruments measure the temperature of the water, the steam, the furnace gases and the air. There are instruments with clockwork mechanisms for measurements involving a time element: for instance, recording steam flow in relation to the load on the turbo-generators at any particular time. Lastly there are chemical instruments for measuring CO2 and photo-electric instruments for measuring smoke.

Turbine house instruments
     Instruments are used in the turbine house to measure the flow of steam into the turbine, its pressure and temperature, the speed of the rotor shaft and the temperature of its bearings, oil pressures of the lubricating system, the expansion of materials and the vacuum created in the condenser by the change of steam into water. The clearances and the temperatures of the generators have to be carefully watched and instruments are needed to record the amount of electricity generated.

A typical job
     Apart from day-to-day maintenance, planned maintenance is done yearly during the summer on certain scheduled instruments which are fundamental to the operating efficiency of the station. An instrument mechanic on these occasions takes the instrument to the workshop and checks it for accuracy against set standards. He then makes all necessary adjustments and repairs it if necessary. This involves dismantling the instrument, cleaning and inspecting parts for wear or breakage, making replacement parts, reassembling, checking and recalibrating, and finally refining and testing on the equipment. For this work an instrument mechanic needs to have a good understanding of electricity and electronics and skill in handling tiny components such as jewel bearings, pinions and spindles. High standards of accuracy are required, often to a thousandth of an inch. Instruments have to be balanced and springs accurately tensioned.