US 5,294,794 AGranted

Automatic compensation for ion mobility sensor

AssigneeThermo King Corporation

InventorDavid K. Davies

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Abstract

A system for compensating for changes in pressure and temperature in an ion mobility sensor has first and second electrodes positioned a selected distance apart, with a unidirectional electric drift field provided between the electrodes. An ionization source generates ions in the sensor and a trigger controller allows ions to enter the region between the first and second electrodes at a time t.sub.1. A time t.sub.2 at which a selected ion species travels to one of the first and second electrodes is measured and a time to amplitude converter generates a voltage signal proportional to the difference between t.sub.1 and t.sub.2, representing the actual travel time of the ion species. A feedback control circuit adjusts the drift field and either the voltage pulse (in pulsed ionization) or the shutter voltage (in continuous ionization) by an amount proportional to the difference between the actual travel time voltage and a voltage proportional to a reference travel time of the selected ion species at a known pressure and temperature.

Claims20

Dependent claims

A system for compensating for changes in pressure and temperature in an ion mobility sensor, the sensor having an ionization region being connected to a drift region, the sensor comprising:

(a) a boundary grid electrode providing a boundary between the ionization region and the drift region;
(b) a second electrode provided at an end of the drift region opposite to the boundary electrode, wherein a voltage potential is applied to the electrodes creating a unidirectional electric field between the electrodes;
(c) an ionization source located in the ionization region proximate the boundary electrode for generating ions in the sensor;
(d) a trigger controller connected to at least one of the boundary electrode and the ionization source for allowing ions to enter the drift region proximate to the boundary electrode at a time t.sub.1 ;
(e) means connected to the second electrode for measuring a time t.sub.2 at which a selected ion species travels from the boundary electrode to the second electrode;
(f) a time to amplitude converter for generating a voltage signal proportional to a difference between t.sub.1 and t.sub.2, the voltage signal representing the actual travel time of the selected ion species from the boundary electrode to the second electrode;
and
(g) a feedback control circuit connected to the time to amplitude converter for adjusting the electrode voltage potential by an amount proportional to a difference between the actual travel time voltage and a voltage proportional to the reference travel time of the selected ion species between the boundary and second electrodes at a known pressure and temperature.

5 more elements

A method of compensating for changes in pressure and temperature in an ion mobility sensor, the sensor having an ionization region being connected to a drift region, the sensor comprising the steps of:

(a) providing a boundary electrode that defines a boundary between the ionization region and the drift region;
(b) providing a second electrode at an end of the drift region opposite to the boundary electrode, wherein a voltage potential is applied to the electrodes creating a unidirectional electric field between the electrodes;
(c) creating ions of a gaseous sample proximate the boundary electrode;
(d) directing the ions into the drift region proximate the boundary electrode at a time t.sub.1 ;
(e) measuring a time t.sub.2 at which a selected ion species travels form the boundary electrode to the second electrode;
(f) generating a voltage signal proportional to a difference between t.sub.1 and t.sub.2, the voltage signal representing the actual travel time of the selected ion species from the boundary electrode to the second electrode;
and
(g) adjusting the electrode voltage potential by an amount proportional to a difference between the actual travel time voltage and a voltage proportional to the reference travel time of the selected ion species between the boundary and second electrodes at a known pressure and temperature.

5 more elements

Dependencies are inferred from the claim text.