Robertson-Thompson Steam Engine Indicator
date: label: date made
content: ca 1900
notes: label: Description
content: This Robertson-Thompson steam engine indicator, serial number 7735, consists of a brass piston with two grooves; a brass cylinder; an internal, single wound spring, which can be changed; a medium sized drum with a coil spring and a single record; and a short pencil lead for the stylus. Accompanying the indicator is a box with two extra springs, drum springs, seven wooden pulleys for the reducer, two scales, and two extra pistons.
label: Description
content: An engine indicator is an instrument for graphically recording the pressure versus piston displacement through an engine stroke cycle. Engineers use the resulting diagram to check the design and performance of the engine.
label: Description
content: A mechanical indicator consists of a piston, spring, stylus, and recording system. The gas pressure of the cylinder deflects the piston and pushes against the spring, creating a linear relationship between the gas pressure and the deflection of the piston against the spring. The deflection is recorded by the stylus on a rotating drum that is connected to the piston. Most indicators incorporate a mechanical linkage to amplify the movement of the piston to increase the scale of the record.
label: Description
content: When the ratio of the frequency of the pressure variation to the natural frequency of the system is small, then the dynamic deflection is equal to the static deflection. To design a system with a high natural frequency, the mass of the piston, spring, stylus, and mechanical linkage must be small, but the stiffness of the spring must be high. The indicator is subjected to high temperatures and pressures and rapid oscillations, imposing a limitation on the reduction in mass. Too stiff a spring will result in a small displacement of the indicator piston and a record too small to measure with accuracy. Multiplication of the displacement will introduce mechanical ad dynamic errors.
label: Description
content: The parameters of the problem for designing an accurate and trouble free recorder are such that there is no easy or simple solution. Studying the variety of indicators in the collection shows how different inventors made different compromises in their designs.
label: Location
content: Currently not on view
place: label: place made
content: United States: New York
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content: Work and Industry: Mechanical and Civil Engineering
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content: Engineering, Building, and Architecture
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content: Work
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content: Industry & Manufacturing
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content: Indicators
creditLine: label: Credit Line
content: Gift of Mr. William Slater Allen, Providence 7, Rhode Island.
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: MC.318483
label: catalog number
content: 318483
label: accession number
content: 234643
objectType: label: Object Name
content: indicator, steam engine
physicalDescription: label: Physical Description
content: metal (overall material)
label: Physical Description
content: wood (container material)
label: Measurements
content: box - from catalog card: 7 in x 9 1/2 in x 10 1/2 in; 17.78 cm x 24.13 cm x 26.67 cm
label: Measurements
content: overall: 7 1/4 in x 6 in x 2 in; 18.415 cm x 15.24 cm x 5.08 cm