Method for measuring the gas pressure in a container, and devices for its application

A method for measuring gas pressure (p) in a vessel having a wall, comprising the steps of:

• providing a pair of spaced apart resistance elements (3, 6) in the vessel at locations which are spaced from the wall of the vessel, the resistance elements being in heat-conducting contact with the wall through the gas;
• passing an electric current through each of the resistance elements;
• measuring electrical variables at at least two different measuring temperatures (T1, T2) in the resistance elements;
• and
• determining the gas pressure (p) as a function of said variables.

An apparatus for measuring gas pressure (p) in a vessel comprising:

• a Wheatstone bridge (1) having an operational amplifier for balancing the bridge, a first branch containing a first resistance element (3) and a second branch containing a second resistance element (6), the first and second resistance elements being adapted for placement in the vessel at a location spaced from the wall of the vessel and the resistance elements being in heat-conducting contact with the wall through the gas, resistances in the bridge being selected so that, at at least one point of a measuring range, linearized dependencies of voltages tapped at a tap of the Wheatstone bridge (1) for the purpose of balancing on measuring temperatures (T1, T2) of the respective resistance elements (3, 6) are identical in the first and second branches;
• means for passing an electric current through the resistance elements;
• and
• means for measuring electrical variables in the resistance elements at the measuring temperatures (T1, T2), the gas pressure (p) being determined as a function of said variables.

An apparatus for measuring gas pressure (p) in a vessel comprising:

• a Wheatstone bridge (1) with an operational amplifier (10) for balancing the bridge, the bridge including a first branch containing a resistance element (3) that is adapted for placement in the vessel at a location spaced from the wall of the vessel, the resistance element being in heat-conducting contact with the wall through the gas in the vessel;
• a switch (14) connected to an output of the operational amplifier (10) and to a constant current source (15) connected to the Wheatstone bridge (1), for at least periodically subjecting the resistance element (3) to a known constant current (10) for determining a resistance of the resistance element (3) from a voltage drop (U0) at the resistance element and for determining a wall temperature (TW) of the vessel wall from said resistance, the wall temperature being useful for determining the gas pressure;
• and
• means for measuring electrical variables in the resistance element at at least two different measuring temperatures (T1, T2) in the vessel for determining the gas pressure (p) as a function of said variables.

An apparatus for measuring gas pressure (p) in a vessel comprising:

• a Wheatstone bridge (1) with an operational amplifier (10) for balancing the bridge, the bridge including a first branch containing a resistance element (3) that is adapted for placement in the vessel at a location spaced from the wall of the vessel, the resistance element being in heat-conducting contact with the wall through the gas in the vessel;
• another amplifier (17) controlled by an amplitude controller (19) and connected as a feed back from an output of the operational amplifier (10) to an input of the operational amplifier;
• and
• means for measuring variables that are associated with the resistance element at at least two different measuring temperatures (T1, T2) in the vessel for determining the gas pressure (p) as a function of said variables.