Ion Science GasCheck Tesla - Manual (Page 8)

GASCHECK TESLA MANUAL Ion Science Ltd
Page 8 of 25
Unrivalled Detection. www.ionscience.com
How GasCheck Tesla works
Thermal Conductivity
All gases conduct heat but by varying amounts, if an object is heated and then the source of heat is
removed, the object will eventually cool down to match ambient air temperature. This action occurs because
the ambient air surrounding the object carries the access heat into the surrounding atmosphere.
This principal is also the same for objects that are cooler than the surrounding ambient air.
Dissipation of heat into an air atmosphere is known and is a predictable rate however, if the ambient air is
replaced with an alternative gas like Helium the rate at which an object cools down changes.
If the object mentioned above had its environment replaced with pure Helium it would cool down to the
environment temperature about 6 times faster.
The GasCheck Tesla contains a heated thermistor bead that transmits heat to a block of material that
remains at a constant temperature. As air passes through the detector chamber a constant amount of heat
passes from the bead to the block. Gases that are different to air will affect the rate at which heat transmits
from the bead to the block, these rates of change are measured and displayed as leak rates.
The diagram below shows the basic functionality of the GasCheck Tesla 's Thermal Conductivity sensor.
A fan draws a small flow of gas through the probe and into the sensing chamber. The thermistor bead heats
up when electrical power is applied. As air passes through the cell a constant level of heat is transmitted to a
Temperature Stable block through the air, this rate of heat transmission is used to 'Zero' the instrument.
When gases with different thermal qualities pass through the chamber the amount of heat being transmitted
to the Temperature Stable block changes. These changes are measured, calculated and displayed on
GasCheck Tesla as leak rates or gas concentrations.
PLEASE NOTE:
* Some gases have similar thermal properties to that of air, therefore the GasCheck Tesla can only detect
larger concentrations of these gases.
* Some gases have positive and other gases negative signals. To simplify the instruments function
GasCheck Tesla only displays changes as positive readings.
* The GasCheck Tesla can NOT differentiate between gases! Selecting a specific gas on the GasCheck
Tesla allows the instrument to calculate concentrations of that gas only if that gas is being detected.
Prob
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Temperature
Stable
Fan
Air flow
Display