Meteor-Optic Simple Tabletop Sympiesometer   |    Ref: ME-TTS001

In its simplest form, the sympiesometer measures the volume of a trapped quantity of air as it varies with the atmospheric pressure. Model TTS001 represents the instrument at this level of simplicity.

The captive gas is contained in the upper bulb connected to the helical tube which dips in some coloured fluid contained in the outer cylinder. A piston, controllable with a brass thumbwheel is provided at the top to adjust the volume of captive air and allow the instrument to be set up. One of the turns of the helix is marked with an index, which represents the position of the liquid level when the pressure is 1000mB. The instrument is so engineered that each turn of the glass coil represents 10millibars of atmospheric pressure. As the atmospheric pressure increases, liquid is driven up the glass coil and compresses the gas above until an equilibrium is reached. Similarly, as the pressure falls the column of liquid descends.

Reading the Sympiesometer.
The purpose of the glass helix is to expand the scale to allow reading to 1 millibar. Turn the instrument so that the index on the 1000 millibar turn is facing you. Note whether the level of the liquid is below or above the index. Note the number of complete turns and the fraction of a turn which lie between the index and the liquid level. Each full turn represents 10 mB and the number of millibars corresponding to the fraction can easily be estimated. If the liquid level is below the index, subtract from 1000 and if above add to 1000 to obtain the atmospheric pressure.

The Problem of Temperature.
The Sympiesometer is thus capable of providing reasonably precise measurements of atmospheric pressure even with its very simple design. Unfortunately temperature also has a marked effect on the liquid level in the helix. Together with the response of 10mB/ turn, the instrument also shows a response to temperature of -3 degrees C/turn. That is, a pressure increase of 10mB will raise the liquid level by 1 turn, and a rise temperature of 3 degrees will cause the liquid level to fall by 1 turn.

Managing the Temperature Response.
The simplest way to cope with the effect of temperature is to keep the temperature constant. Find a place in which to stand your Sympiesometer, away from draughts, and where the temperature is constant as possible.
Otherwise you can measure the temperature when setting up and then when reading the instrument and make the appropriate allowance for temperature.

Dimensions:
360mm Height
approx 55mm Diameter