. Electric railway journal . cted across anexternal shunt. The moving element consists of a simple metaldisk or sector rigidly attached to a shaft carrying the recordingpen mounting and control springs. The moving disk is floatedin a mercury chamber which not only serves as a conductingmedium for the current to be measured, but also by the damp-ing action of the disk passing through the mercury renders themeter indications highly aperiodic or dead beat. This is a veryimportant and desirable feature when meters are measuringfluctuating loads, as it insures a true record free from false in-dicat
. Electric railway journal . cted across anexternal shunt. The moving element consists of a simple metaldisk or sector rigidly attached to a shaft carrying the recordingpen mounting and control springs. The moving disk is floatedin a mercury chamber which not only serves as a conductingmedium for the current to be measured, but also by the damp-ing action of the disk passing through the mercury renders themeter indications highly aperiodic or dead beat. This is a veryimportant and desirable feature when meters are measuringfluctuating loads, as it insures a true record free from false in-dications or overshooting. Surrounding the moving disk is a magnetic field generatedby electromagnets in the wattmeter and permanent magnetsin the ammeters. The magnetic field of the fixed elements isin such relative position to the moving system or armaturethat it cuts or passes through the armature field and tends torotate the moving system. This rotative movement causesthe recording pen to move across the chart against the re-. Fig. 1 Shunted Type Switch-board Wattmeter straining force of the control springs, wiiich tend to returnthe pen to zero position. The turning force of the mercury-floated moving element is thus balanced against the restrainingor coercive force of the control springs and their point ofbalance or equilibrium is a measure of the current flowing inthe measuring coils. As the meters are of the direct deflection type the use ofrelays, control magnets, contacts, etc., with their attendanttrouble, is entirely avoided. The construction adopted isalso said to be unique in that it secures a torque or turningmoment much higher than has been heretofore attained. Thishigh torque in conjunction with the minimum friction value ofthe mercury floated moving element gives a ratio of torqueto weight and friction of such value that errors due to penfriction on the chart are eliminated. An important feature is that the moving element of themeasuring system is inherently da
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