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A202-25 · Aneroid
c.1930
Object Overview
This Cabin Aneroid Barometer, dating from around 1930, was manufactured at the Leningrad State Plant of Meteorological Instruments in the Soviet Union. The barometer is housed in a barrel-shaped case of nickel-plated brass, featuring a narrow bezel that secures a mineral glass with a faceted edge.
The open dial is made of silvered brass and fitted with a reflective ring. The barometric scale is concentrically engraved around the circumference and calibrated in centimeters of mercury, ranging from 60 to 79. Each centimeter is subdivided into twentieths. In the lower part of the dial is an aperture for a curved mercury thermometer, mounted beneath the dial and fixed to the rear surface of the dial plate. The thermometer scale, engraved directly on the dial, is graduated in degrees Celsius. The delicate blued-steel pointer, of flattened form and without a counterweight, terminates in a slightly widened indicating tip.
At the heart of the instrument lies an exceptionally refined and technically intriguing movement. Mounted on a painted cast-iron base is a seven-centimeter aneroid capsule made of nickel silver (German silver), supported by a C-shaped steel spring whose outer end is fixed to a massive cast-iron lever. The lever rests on two bearings and features an offset arm fitted with an adjustment screw, whose head is accessible from the back of the barometer case.
314308
aneroid capsule tensioned on a C-spring
cast iron, glass, nickel silver, nickel-plated brass, silvered brass, steel
From the spring plate to the main pivot mechanism extends the temperature-compensated primary lever. The temperature correction is achieved by means of an adjustable bimetallic compensator — a telescopic assembly with a threaded sleeve and a spring element. One of its components is made of a metal with a different coefficient of thermal expansion (such as invar or brass), while the other is steel. As the temperature changes, the differential expansion produces a minute rotation and vertical displacement of the lever’s lower arm, subtly altering the transmission ratio at the point of contact with the actuator. In this way, temperature-induced errors in capsule elasticity are compensated mechanically by a change in lever geometry.
The main lever connects via a linkage to the primary shaft, which carries a counterweight on one side and a spindle on the other. The spindle is fitted with two square-headed adjustment screws, characteristic of early aneroid designs, used for fine mechanical calibration of the lever’s amplitude. The adjustment is achieved by widening or narrowing the clearance between the shaft and lever spindle. The vertical arm of the main shaft is coupled to the pointer arbor through a delicate chain and extension linkage, the opposite end of which winds directly onto the pointer axis.
A particularly notable feature is the bridge construction, where the bridge supporting the pointer arbor is directly connected to the main shaft, forming a single integral unit. All components of the lever system are finely nickel-plated, revealing the remarkable precision and craftsmanship of Soviet instrument-making during this period.
This Leningrad-made barometer represents one of the most advanced Soviet adaptations of the European cabin aneroid design — a synthesis of classical mechanical engineering, meticulous finishing, and innovative thermal compensation rarely encountered in instruments of its era.