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Module Helium Detector

IP.com Disclosure Number: IPCOM000042586D
Original Publication Date: 1984-May-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

O'Hanlon, JF: AUTHOR

Abstract

Helium Detection Test The module contains a thermistor used to monitor the temperature of the module during operation. Its characteristic is shown in Fig. 1. The thermistor is heated with a direct current. The temperature will rise so that the heat out equals the heat input. Heat input = I2 Rthermistor Heat out = Kg (Tth-TGAS) + Radiation + End Losses Losses A gas with a high thermal conductivity will heat less than a gas with a low thermal conductivity. Helium has a very high thermal conductivity so its temperature rise is less than any other gas except hydrogen. Typical conductivities are: (Image Omitted) The thermal conductivity of any gas below a pressure of, say, 0.010 Torr is negligible so this technique can detect evacuated modules.

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Module Helium Detector

Helium Detection Test The module contains a thermistor used to monitor the temperature of the module during operation. Its characteristic is shown in Fig. 1. The thermistor is heated with a direct current. The temperature will rise so that the heat out equals the heat input. Heat input = I2 Rthermistor Heat out = Kg (Tth-TGAS) + Radiation + End Losses Losses A gas with a high thermal conductivity will heat less than a gas with a low thermal conductivity. Helium has a very high thermal conductivity so its temperature rise is less than any other gas except hydrogen. Typical conductivities are:

(Image Omitted)

The thermal conductivity of any gas below a pressure of, say, 0.010 Torr is negligible so this technique can detect evacuated modules. The thermal conductivity of helium-air mixtures changes enough after 10% air contamination so that these mixtures can also be detected. Technique Step 1 Apply 10 volts to a series resistor-thermistor (Fig. 2).

(Image Omitted)

Step 2 Apply 75 volts DC to the same resistor-thermistor combination. The temperature will rise according to the gas species, and the temperature is:

(Image Omitted)

The net temperature rise is:

(Image Omitted)

The heat dissipation of a thermistor is also sensitive to gas mixtures. Shown in Fig. 3 is a plot of temperature rise versus % air contamination in 2 atmospheres helium. If we allow for variation in thermistors, we can safely pick up 30% air contamination, while, if the initia...