Tasimeter

Tasimeter (cross section)

A tasimeter or microtasimeter (Greek, “extensometer”) is an instrument developed by Thomas Alva Edison for fine thermometric observations.

functionality

The function of the tasimeter is based on the change in the galvanic resistance of the carbon , which is known from the microphone, by changing the pressure, with which the expansion of the body through heat, moisture, etc. can be detected.

On a strong iron base plate, 10 cm apart, rise two short, thick cones cast in one piece with the plate, between which the rod-shaped body, which is to be tested for its expansion and which is pointed at its ends, is brought into a horizontal position. One end of the rod is received in the cavity of a screw which passes through the one pin.

A vertically standing platinum plate is screwed to the other pin, which at the same time holds a cylindrically hollowed disk made of hard rubber . A plate of carbon lies against the platinum plate, followed by a platinum sheet, against which a brass plate presses, which is provided with a cavity for receiving the other end of the rod.

The second pin on the one hand and the platinum sheet on the other hand are connected to the wires of a line in which a galvanic element and a galvanometer are connected. If the rod expands and presses the platinum sheet more strongly against the carbon plate, the resistance is reduced and the galvanometer gives a greater deflection.

The expansion of a stick of hard rubber by the heat of the hand held several inches away causes the galvanometer needle to deflect several degrees; even a strip of mica is noticeably affected by the warmth of the hand. A stick of gelatin is immediately expanded by the steam from a moist piece of paper 7-8 cm away. The instrument is therefore suitable for fine thermometric and hygrometric observations.

literature

Tasimēter . In: Meyers Konversations-Lexikon . 4th edition. Volume 15, Verlag des Bibliographisches Institut, Leipzig / Vienna 1885–1892, p. 528.
The micro-tasimeter . In: The Gazebo . Issue 39, 1878, pp. 648 ( full text [ Wikisource ]).